Companion reviews: Adult ADHD and the evidence, ADHD medications and the evidence, Diagnostic Thresholds and the Evidence, Placebo, unblinding and the evidence, Depression — antidepressants and the evidence, Antipsychotics and the Evidence, Mood stabilizers and the evidence, and Benzodiazepines and the Evidence.

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Executive summary

Two folk models dominate public discussion of ADHD and stimulants: that ADHD is not a real disorder but a medicalization of childhood behavior (the invalidation narrative), and its inversion, that ADHD is a discrete brain disorder corrected by stimulants (the neurobiological-deficit story). Both are overclaims, and the evidence supports neither.

Eight things the evidence actually establishes:

1. Stimulants reduce ADHD symptoms acutely compared to placebo, with effect sizes that vary by rater. The Cochrane systematic review of methylphenidate (212 trials, 16,302 participants) found teacher-rated symptom reduction of SMD −0.74 (95% CI −0.88 to −0.61), but the certainty of this evidence was rated very low. The network meta-analysis by Cortese et al. (2018) found clinician-rated effect sizes of SMD −1.02 for amphetamines and −0.78 for methylphenidate, while teacher ratings showed methylphenidate at −0.82 and amphetamines were not significantly different from placebo on teacher ratings. Effect sizes are larger when rated by clinicians than by teachers, and parent ratings typically fall between the two (Storebø et al., 2023; Cortese et al., 2018).

2. The 14-month MTA trial found medication management superior to behavioral treatment for core ADHD symptoms, but the treatment-by-protocol phase told only part of the story. Among 579 children aged 7–9.9 years assigned to medication management, behavioral treatment, combined treatment, or community care, medication management and combined treatment showed significantly greater improvement than behavioral treatment and community care on parent- and teacher-rated inattention and teacher-rated hyperactivity-impulsivity. Combined treatment used lower doses (31.2 mg/day methylphenidate) than medication management alone (37.7 mg/day), but the two did not differ on core ADHD symptoms. All four groups showed sizable reductions in symptoms over time (MTA Cooperative Group, 1999).

3. By 36 months, the initial treatment advantage had disappeared, and by 8 years, original treatment assignment did not predict outcomes. At the 36-month follow-up—22 months after the randomized trial ended—treatment groups no longer differed significantly on any measure. Medication use changed substantially: the behavioral treatment group increased from 14% to 45% on medication, while medication management and combined treatment decreased from 91% to 71%. Regardless of treatment changes, all groups showed symptom improvement over baseline, but the earlier advantage of medication management was no longer apparent (Jensen et al., 2007). At 6 and 8 years, original treatment assignment did not predict functioning; instead, ADHD symptom trajectory in the first 3 years predicted 55% of outcomes. Type or intensity of the initial 14-month treatment did not predict functioning 6–8 years later (Molina et al., 2009).

4. Extended stimulant use is associated with height suppression but not with reduction in symptom severity in young adulthood. In the 16-year MTA follow-up (mean age 24.7 years), the ADHD group showed symptom persistence compared to local norms. Within naturalistic subgroups of ADHD cases, the treated group with the consistent or inconsistent pattern was 2.55 ± 0.73 cm shorter than the subgroup with negligible use (p < 0.0005, d = 0.42), and within the treated group, those with consistent use were 2.36 ± 1.13 cm shorter than those with inconsistent use (p < 0.04, d = 0.38). However, comparisons of naturalistic subgroups reflecting medication effects were not significant for symptom severity (Swanson et al., 2017).

5. Parent-teacher rating disagreement is substantial and reflects situation-specific behavior, not measurement error. Studies of parent-teacher agreement find correlations ranging from low to moderate (0.34–0.64 on the Strengths and Difficulties Questionnaire; 0.17–0.60 on CBCL attentional problems). Measurement invariance testing shows that 7 of 9 inattention items and 6 of 9 hyperactivity-impulsivity items exhibit substantial measurement non-invariance between parents and teachers, with correlations between parent and teacher ratings for 6 inattention items and 4 hyperactivity-impulsivity items not significantly different from zero. This suggests parents and teachers rate different behaviors expressed in different settings, not the same behavior with added noise (Gomez, 2019).

6. The certainty of evidence for stimulant efficacy and safety is very low, and most trials are short-term. The Storebø et al. (2023) Cochrane review rated 191 of 212 trials as high risk of bias and 21 as low risk. If deblinding of methylphenidate due to typical adverse events is considered, then all 212 trials were at high risk of bias. Methylphenidate treatment duration ranged from 1 to 425 days, with a mean duration of 28.8 days. Certainty of evidence for teacher-rated ADHD symptoms was very low, and the same for serious adverse events. Trial durations in the Cortese et al. (2018) network meta-analysis ranged from 1 to 24 weeks, with most under 12 weeks. Blinding is compromised by easily recognized side effects (decreased appetite, sleep problems), and active placebos that mimic these effects are rarely used.

7. Stimulants produce small, statistically significant increases in blood pressure and heart rate. Meta-analysis of 18 trials (5,837 participants, mean duration 28.7 weeks) found that methylphenidate increased systolic blood pressure (SMD 0.25, 95% CI 0.08–0.42) but not diastolic blood pressure or heart rate. Amphetamines increased systolic blood pressure (SMD 0.09, 95% CI 0.03–0.15), diastolic blood pressure (SMD 0.16, 95% CI 0.03–0.29), and heart rate (SMD 0.37, 95% CI 0.13–0.60). Atomoxetine showed similar patterns. Head-to-head comparisons showed no significant differences among the three medications. About 2% of patients discontinued medication due to cardiovascular effects (Liang et al., 2018).

8. ADHD prevalence estimates are stable across three decades when standardized diagnostic procedures are followed. Systematic reviews find that variability in prevalence estimates (ranging from 5% to over 10%) is explained by methodological factors: diagnostic criteria used (DSM-III vs DSM-IV vs DSM-5), requirement for impairment, and source of information (parent only, teacher only, "or" rule, "and" rule, best-estimate procedure). A meta-regression of 135 studies found no association between year of study and prevalence estimates. When standardized diagnostic procedures are followed, there is no evidence of an increase in the number of children meeting ADHD criteria over the past three decades (Polanczyk et al., 2014; Thomas et al., 2015).

What the evidence does not establish:

• That ADHD symptoms arise from a correctable neurotransmitter deficit (the dopamine hypothesis faces the same logical problem as the serotonin hypothesis in depression)
• That stimulants improve long-term functional outcomes (academic achievement, occupational outcomes, substance use, arrests) beyond their acute symptomatic effects
• That early stimulant treatment alters the natural course of the disorder
• Which children will respond to stimulants or which dose will be optimal
• That parent-teacher disagreement reflects unreliable measurement rather than situation-specific behavior

The structural problem that conditions all of this: Most trials are short-term, unblinded in practice due to easily recognized side effects, and the evidence certainty is very low. The MTA—the largest, longest, and most carefully conducted trial—showed that initial treatment advantage disappeared after the randomized phase ended, and original treatment assignment did not predict outcomes 6–8 years later. Early symptom trajectory and baseline sociodemographic factors predicted long-term outcomes better than treatment type or intensity. Stimulants reduce symptoms acutely, but the benefits do not appear to compound over time or translate into improved functional outcomes in adulthood.

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How to read this review

The single most important heuristic

An effect size without a named rater is not a finding. Stimulants show larger effects on clinician ratings than on teacher ratings. Teacher ratings show larger effects than parent ratings in some analyses, though not all. Parent and teacher ratings of the same child often disagree substantially—not because measurement is unreliable, but because they observe different behaviors in different settings. Any effect size quoted without specifying who rated it should be assumed to be the most favorable version available.

Three structural problems

Certainty of evidence is very low. The Storebø et al. (2023) Cochrane review rated the certainty of evidence for methylphenidate as very low for teacher-rated ADHD symptoms and for serious adverse events. Of 212 trials, 191 were assessed at high risk of bias and 21 at low risk. If, however, deblinding of methylphenidate due to typical adverse events is considered, then all 212 trials were at high risk of bias. Blinding is compromised by easily recognized side effects (decreased appetite, sleep problems). The authors conclude: "the true magnitude of effects remain unclear."

Trial duration is short. Most efficacy trials last weeks to months. The Cortese et al. (2018) network meta-analysis included trials ranging from 1 to 24 weeks, with the efficacy analysis closest to 12 weeks based on 10,068 children and adolescents. The MTA was unusual in running 14 months under randomized conditions, but even that trial transitioned to naturalistic follow-up afterward, and treatment groups converged by 36 months.

Rater unblinding and informant variance. Decreased appetite and sleep problems occur in 15–30% of children on methylphenidate and are easily recognized. Active placebos that mimic these side effects are rarely used. This means most "double-blind" trials are effectively unblinded for parents and teachers. Additionally, parents and teachers disagree substantially on symptom ratings—not because of measurement error, but because they observe different behaviors in different contexts. Combining ratings from multiple informants using an "or" rule inflates prevalence; using an "and" rule deflates it.

Conventions

Claims are marked [contested] where the literature genuinely disagrees and [unverified] where a figure is widely repeated but could not be traced to a primary source in preparing this review.

Confidence intervals are omitted where they could not be verified against the primary text, rather than reconstructed.

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Part I — What ADHD ratings actually measure, and why parent-teacher disagreement is a finding

1.1 The measurement problem: parent-teacher correlations are low to moderate

Studies consistently find that parent and teacher ADHD symptom ratings correlate at low-to-moderate levels. On the Strengths and Difficulties Questionnaire hyperactivity-inattention subscale, correlations range from 0.34 to 0.64. On DSM-based attentional problems using the Child Behavior Checklist, correlations range from 0.17 to 0.60 (De Los Reyes et al., 2015; as cited in Gomez, 2019).

This is not unique to ADHD. Across all forms of pediatric psychopathology, correlations among informants typically range from low to moderate. But the standard response—that low agreement reflects "measurement error" or "unreliable reporting"—is incorrect.

Parents and teachers observe different behaviors in different settings. Children's behavior varies by context. A child may be inattentive and disruptive in a classroom with 30 peers and structured tasks, but not at home with one-on-one parental attention. Conversely, a child may struggle with homework completion and family routines at home but function adequately in school with external structure provided by the teacher.

The question, then, is whether parent-teacher disagreement reflects (1) measurement bias (one or both raters are unreliable), or (2) situation-specific behavior (both raters are reliable, but they observe different behaviors in different contexts).

1.2 Measurement invariance testing: parents and teachers rate different behaviors

Measurement invariance testing using confirmatory factor analysis addresses this question directly. It asks: Are parents and teachers rating the same underlying construct (ADHD) in the same way, or do they interpret and endorse symptom criteria differently?

Gomez (2019) analyzed parent and teacher ratings in the IMAGE dataset (children with ADHD and their siblings) using latent trait models. The study found substantial measurement non-invariance between parent and teacher ratings for 7 of 9 inattention items and 6 of 9 hyperactivity-impulsivity items. Critically, the correlations between parent and teacher ratings for 6 inattention items and 4 hyperactivity-impulsivity items were not significantly different from zero.

What this means: For most ADHD symptom items, parents and teachers are not rating the same behaviors with added noise. They are rating different behaviors expressed in different settings. This is not measurement error; it is a finding.

Conversely, within informants, age and gender did not substantially affect symptom endorsement probabilities. Teacher ratings were largely unaffected by comorbid oppositional defiant disorder, conduct disorder, or anxiety disorders. Parental endorsement of hyperactivity-impulsivity symptoms was more influenced by comorbid ODD, but even this effect was modest.

1.3 What this means for diagnosis and effect sizes

Clinicians are advised to integrate information from multiple informants when diagnosing ADHD. But the method of combination matters:

• "Or" rule (child meets criteria according to parent or teacher): inflates prevalence and includes children whose symptoms are context-specific.
• "And" rule (child meets criteria according to parent and teacher): deflates prevalence and excludes children whose symptoms are severe in one context but not the other.
• Best-estimate procedure (clinician integrates information from multiple sources using clinical judgment): produces intermediate prevalence estimates, but introduces clinician judgment as a variable.

The worldwide-pooled prevalence of ADHD varies substantially depending on the diagnostic method. Studies using DSM-IV criteria without impairment requirements report higher prevalence than those requiring impairment. Studies relying on parent-only or teacher-only information report higher prevalence than those requiring convergence across informants (Polanczyk et al., 2007).

Effect sizes in trials depend on who rates the outcome. In the Cortese et al. (2018) network meta-analysis, amphetamines showed an SMD of −1.02 on clinician ratings but were not significantly better than placebo on teacher ratings in available comparisons. Methylphenidate showed an SMD of −0.78 on clinician ratings and −0.82 on teacher ratings. Parent ratings typically fall between clinician and teacher ratings in magnitude, but not always.

This is not a methodological problem to be solved. It is the reality that ADHD symptoms are context-dependent, and different informants observe different samples of behavior.

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Part II — Acute efficacy: what stimulants actually do, and for how long

2.1 The Cochrane systematic review: very low certainty evidence

Storebø et al. (2023) conducted a systematic review and meta-analysis of methylphenidate for children and adolescents with ADHD. The review included 212 randomized controlled trials with 16,302 participants. Methylphenidate treatment duration ranged from 1 to 425 days, with a mean duration of 28.8 days.

Teacher-rated ADHD symptoms: Methylphenidate versus placebo may improve teacher-rated ADHD symptoms (SMD −0.74, 95% CI −0.88 to −0.61; 21 trials, 1,728 participants; very low certainty evidence). This corresponds to a mean difference of −10.58 points (95% CI −12.58 to −8.72) on the ADHD Rating Scale (range 0 to 72 points). The minimal clinically relevant difference is considered to be a change of 6.6 points on the ADHD-RS.

Serious adverse events: Methylphenidate may not affect serious adverse events (RR 0.80, 95% CI 0.39 to 1.67; 26 trials, 3,673 participants; very low certainty evidence). The trial sequential analysis-adjusted intervention effect was RR 0.91 (95% CI 0.31 to 2.68).

Non-serious adverse events: Methylphenidate may cause more non-serious adverse events versus placebo (RR 1.23, 95% CI 1.11 to 1.37; 35 trials, 5,342 participants; very low certainty evidence). The most common were decreased appetite and sleep problems.

Quality of evidence: Of 212 trials, 191 were assessed at high risk of bias and 21 at low risk. If, however, deblinding of methylphenidate due to typical adverse events is considered, then all 212 trials were at high risk of bias. The authors conclude: "the certainty of the evidence for all outcomes is very low and therefore the true magnitude of effects remain unclear."

2.2 The network meta-analysis: all stimulants beat placebo, but rater matters

Cortese et al. (2018) conducted a systematic review and network meta-analysis of 133 randomized controlled trials (10,068 children and adolescents, 8,131 adults) comparing medications for ADHD. Trial durations ranged from 1 to 24 weeks.

Children and adolescents (clinician ratings): All included drugs were superior to placebo. Effect sizes (SMD) closest to 12 weeks:

• Amphetamines: −1.02 (95% CI −1.19 to −0.85)
• Methylphenidate: −0.78 (95% CI −0.93 to −0.62)
• Atomoxetine: −0.56 (95% CI −0.66 to −0.45)

Children and adolescents (teacher ratings): Available comparisons based on teacher ratings showed that only methylphenidate (SMD −0.82, 95% CI −1.16 to −0.48) and modafinil (−0.76, 95% CI −1.15 to −0.37) were more efficacious than placebo. Amphetamines were not significantly different from placebo on teacher ratings in the available comparisons.

Adults (clinician ratings): Amphetamines (SMD −0.79, 95% CI −0.99 to −0.58), methylphenidate (−0.49, 95% CI −0.64 to −0.35), bupropion (−0.46, 95% CI −0.85 to −0.07), and atomoxetine (−0.45, 95% CI −0.58 to −0.32) were better than placebo. Modafinil was not (0.16, 95% CI −0.28 to 0.59).

Tolerability: Amphetamines were inferior to placebo (more likely to cause discontinuation due to adverse events) in both children and adolescents (OR 2.30, 95% CI 1.36–3.89) and adults (OR 3.26, 95% CI 1.54–6.92). Atomoxetine and methylphenidate showed similar patterns in adults.

Head-to-head comparisons: Amphetamines were more efficacious than modafinil, atomoxetine, and methylphenidate on clinician ratings in both children and adolescents (SMD differences −0.46 to −0.24) and adults (−0.94 to −0.29). However, the confidence of estimates varied from high or moderate for some comparisons to low or very low for most indirect comparisons.

2.3 The MTA trial: medication management superior at 14 months

The Multimodal Treatment Study of Children with ADHD (MTA) randomized 579 children aged 7 to 9.9 years with ADHD Combined Type to 14 months of:

1. Medication management (titration followed by monthly visits)
2. Intensive behavioral treatment (parent training, teacher consultation, summer treatment program, classroom aide)
3. Combined treatment (both medication management and behavioral treatment)
4. Community care (treatment by community providers)

Medication management protocol: The medication arm used a 28-day double-blind daily-switch titration of methylphenidate, with doses of placebo, 5 mg, 10 mg, and 15 or 20 mg (higher for children >25 kg) given at breakfast and lunch, with a half-dose in the afternoon. Cross-site teams of clinicians blindly reviewed parent and teacher ratings and selected each child's best dose by consensus. Of 289 subjects assigned to medication management or combined treatment, 256 (88.6%) completed titration, and 198 (68.5%) were assigned to an individually titrated best dose of methylphenidate, with average initial doses of 30.5 mg/day. By study end, 73.4% were maintained on methylphenidate, 10.4% on dextroamphetamine, 1.4% on pemoline, 1.0% on imipramine, and smaller numbers on other medications or no medication (MTA Cooperative Group, 1999).

Results at 14 months: All four groups showed sizable reductions in symptoms over time, with significant differences among them in degrees of change. For ADHD symptoms, medication management and combined treatment showed significantly greater improvement than behavioral treatment and community care. Medication management and combined treatment did not differ significantly on direct comparisons of core ADHD symptoms.

Combined treatment used lower doses (mean 31.2 mg/day methylphenidate) than medication management alone (mean 37.7 mg/day), consistent with prior literature showing that multimodal treatment allows dose reduction.

For non-ADHD outcomes (oppositional/aggressive symptoms, internalizing symptoms, social skills, parent-child relations, reading achievement), combined treatment showed modest advantages over medication management alone, and medication management did not consistently outperform behavioral treatment or community care on these outcomes. But these differences were smaller in magnitude than the core ADHD symptom effects.

Community care: Two-thirds of community care subjects (67.4%) received ADHD medications from their own providers during the 14 months, most commonly methylphenidate (n = 84), with a mean total daily dose of 22.6 mg/day (versus 30.5–37.7 mg/day in the medication management arms). The MTA medication strategies were superior to community care despite the fact that most community care subjects received medication.

2.4 The 36-month follow-up: treatment groups converge

Jensen et al. (2007) reported outcomes at 36 months—22 months after the 14-month randomized trial ended. At this point, 485 of the original 579 subjects (83.8%) participated, now aged 10–13 years (mean 11.9 years).

Key finding: In contrast to the significant advantage of medication management and combined treatment over behavioral treatment and community care at 14 and 24 months, treatment groups did not differ significantly on any measure at 36 months.

Medication use changes: The percentage of children taking medication >50% of the time changed substantially between 14 and 36 months:

• Behavioral treatment: increased from 14% to 45%
• Medication management and combined treatment: decreased from 91% to 71%
• Community care: remained constant at 60–62%

Regardless of treatment changes, all groups showed symptom improvement over baseline. The authors note: "By 36 months, the earlier advantage of having had 14 months of the medication algorithm was no longer apparent, possibly due to age-related decline in ADHD symptoms, changes in medication management intensity, starting or stopping medications altogether, or other factors not yet evaluated."

Predictors of outcomes: Initial symptom severity, sex (male), comorbidity, public assistance, and parental ADHD did not moderate 36-month treatment responses, but these factors predicted worse outcomes over 36 months, regardless of original treatment assignment.

2.5 The 8-year follow-up: original treatment assignment does not predict outcomes

Molina et al. (2009) reported outcomes at 6 and 8 years after randomization, when the sample ranged in age from 13–18 years. Retention was 436 of the original 579 MTA participants (75.3%) and 261 of 289 local normative comparison group participants (90.3%).

Key finding: In nearly every analysis, the originally randomized treatment groups did not differ significantly on repeated measures or newly analyzed variables (e.g., grades earned in school, arrests, psychiatric hospitalizations, other clinically relevant outcomes). Medication use had decreased by 62% after the 14-month controlled trial, but adjusting for this did not change the results.

What did predict outcomes? ADHD symptom trajectory in the first 3 years predicted 55% of the outcomes measured at 6 and 8 years. Early symptom improvement—regardless of which treatment produced it—was prognostic. Children with behavioral and sociodemographic advantages, with the best response to any treatment, had the best long-term prognosis.

Comparison to local norms: The MTA participants fared worse than the local normative comparison group on 91% of the variables tested. Despite initial symptom improvement during treatment that was largely maintained after treatment, children with combined-type ADHD exhibited significant impairment in adolescence.

The authors' conclusion: "Type or intensity of 14 months of treatment for ADHD in childhood (at age 7.0–9.9 years) does not predict functioning 6 to 8 years later. Rather, early ADHD symptom trajectory regardless of treatment type is prognostic. This finding implies that children with behavioral and sociodemographic advantage, with the best response to any treatment, will have the best long-term prognosis."

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Part III — Long-term outcomes: height suppression and symptom persistence

3.1 Height suppression in the 16-year follow-up

Two papers from the MTA follow-up report height outcomes. Swanson et al. (2017) analyzed endpoint comparisons at 16 years (mean age 24.7), finding that the ADHD group was 1.29 ± 0.55 cm shorter than the local normative comparison group (LNCG) (p < 0.01, d = 0.21). Within naturalistic subgroups of ADHD cases, the treated group with the consistent or inconsistent pattern was 2.55 ± 0.73 cm shorter than the subgroup with negligible use (p < 0.0005, d = 0.42), and within the treated group, those with consistent use were 2.36 ± 1.13 cm shorter than those with inconsistent use (p < 0.04, d = 0.38).

Swanson et al. (2019) analyzed height, weight, and BMI trajectories from childhood to adulthood across all 8 assessment points over 16 years. Of 579 children with ADHD-combined type at baseline (aged 7.0–9.9 years) and 289 classmates (LNCG), 568 and 258 respectively were assessed. Parent interview data established subgroups with self-selected stimulant medication use patterns:

• Consistent: n = 53 (9%)
• Inconsistent: n = 374 (66%)
• Negligible: n = 141 (25%)
• Started stimulants prior to MTA entry: n = 211 (39%)

Height trajectories: Height z-score trajectories differed among subgroups (F = 2.22, p < 0.0001) and by stimulant use prior to study entry (F = 2.22, p < 0.001). The subgroup-by-assessment interaction was significant (F = 2.81, p < 0.0001). Paired comparisons revealed significant subgroup differences at endpoint:

• Consistent was shorter than Negligible: −0.66 z units / −4.06 cm / −1.6 inches (t = −3.17, p < 0.0016)
• Consistent was shorter than Inconsistent: −0.45 z units / −2.74 cm / −1.08 inches (t = −2.39, p < 0.0172)
• Consistent was shorter than LNCG: −0.54 z units / −3.34 cm / −1.31 inches (t = −3.30, p < 0.001)

Weight trajectories: Weight z-scores initially diverged among subgroups, converged in adolescence, and then diverged again in adulthood when the Consistent subgroup outweighed the LNCG (+3.561 z units / +7.47 kg / +16.46 lb, p < 0.0001).

Critical periods: Trajectory analysis identified periods at mean age 11.7 years and mean age 14.9 years as times when height trajectories diverged most sharply between subgroups.

The authors' conclusion (Swanson et al., 2019): "Compared with those negligibly medicated and the LNCG, 16 years of consistent stimulant treatment of children with ADHD in the MTA was associated with changes in height trajectory, a reduction in adult height, and an increase in weight and body mass index."

3.2 Symptom persistence without medication benefit

In the same 16-year follow-up, Swanson et al. (2017) also analyzed symptom severity outcomes. For ratings of symptom severity in young adulthood (at 25 years of age), the ADHD-LNCG comparison was statistically significant for the parent/self-report average (0.51 ± 0.04, p < 0.0001, d = 1.11), documenting symptom persistence.

Source discrepancy: The parent/self-report difference was also significant (0.21 ± 0.04, p < 0.0001, d = 0.60), documenting source discrepancy—even in adulthood, different informants (parents versus self) disagree on symptom severity.

Medication effects on symptoms: The comparisons of naturalistic subgroups reflecting medication effects were not significant for symptom severity. Extended use of medication was associated with suppression of adult height but not with reduction of symptom severity.

This finding is consistent with the 8-year follow-up: original treatment assignment and cumulative medication exposure did not predict symptom outcomes in adolescence or young adulthood. Symptom trajectory in the first 3 years—reflecting a combination of treatment response, baseline severity, and sociodemographic factors—predicted outcomes better than treatment type or cumulative medication exposure.

3.3 Functional outcomes in the 16-year follow-up

Hechtman et al. (2016) reported functional adult outcomes at 16 years post-baseline (mean age 24.7 years, range 19–28 years). Retention was 476 of 579 (82%) for the ADHD group and 241 of 258 (93%) for the non-ADHD local normative comparison group.

The analysis compared three groups:

1. ADHD-persistent (met DSM-5 criteria in adulthood)
2. ADHD-desistent (did not meet criteria in adulthood)
3. Local normative comparison group (LNCG)

Educational outcomes: ADHD-persistent adults were significantly less likely than the LNCG to have graduated from high school or obtained a post-secondary degree. ADHD-desistent outcomes were intermediate and did not differ significantly from either ADHD-persistent or LNCG.

Occupational outcomes: ADHD-persistent adults were significantly less likely to be employed full-time and more likely to have been fired or quit a job, compared to the LNCG. ADHD-desistent outcomes were again intermediate.

Legal outcomes: ADHD-persistent adults had more arrests than the LNCG.

Substance use outcomes: ADHD groups did not differ significantly from the LNCG on alcohol or cannabis use frequency.

Critically, these outcomes were not predicted by original treatment assignment. The persistence versus desistence of ADHD symptoms in adulthood predicted functional outcomes, but the type of treatment received in childhood (medication management, behavioral treatment, combined treatment, or community care) did not.

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Part IV — Adverse effects: cardiovascular changes, appetite, and sleep

4.1 Cardiovascular effects: small increases in blood pressure and heart rate

Liang et al. (2018) conducted a systematic review and meta-analysis of 18 clinical trials (5,837 participants, 80.7% boys, average duration 28.7 weeks) assessing the effects of methylphenidate, amphetamines, and atomoxetine on blood pressure and heart rate in children and adolescents with ADHD.

Systolic blood pressure: All three medications were associated with a small but statistically significant pre-post increase:

• Methylphenidate: SMD 0.25 (95% CI 0.08–0.42, p < 0.01)
• Amphetamines: SMD 0.09 (95% CI 0.03–0.15, p < 0.01)
• Atomoxetine: SMD 0.16 (95% CI 0.04–0.27, p = 0.01)

Diastolic blood pressure: Methylphenidate did not have a pre-post effect on DBP. Amphetamines (SMD 0.16, 95% CI 0.03–0.29, p = 0.02) and atomoxetine (SMD 0.22, 95% CI 0.10–0.34, p < 0.01) were associated with small but statistically significant increases.

Heart rate: Methylphenidate did not have a pre-post effect on HR. Amphetamines (SMD 0.37, 95% CI 0.13–0.60, p < 0.01) and atomoxetine (SMD 0.43, 95% CI 0.26–0.60, p < 0.01) were associated with small to medium statistically significant increases.

Head-to-head comparisons: Comparisons among the three medications did not reveal significant differences.

Discontinuation due to cardiovascular effects: About 2% of patients discontinued their medication treatment due to cardiovascular effects. In the majority of patients, cardiovascular effects were tolerated without requiring dose adjustment or discontinuation.

Sensitivity analyses: Amphetamine studies of <18 weeks reported higher effect sizes on DBP compared with longer-duration studies (F(1) = 19.55, p = 0.05). Methylphenidate studies published before 2007 reported higher effect sizes on SBP than studies after 2007 (F(1) = 5.346, p = 0.05).

4.2 Decreased appetite and sleep problems

The Storebø et al. (2023) Cochrane review found that methylphenidate was associated with an increased risk of non-serious adverse events compared to placebo (RR 1.23, 95% CI 1.11 to 1.37; 35 trials, 5,342 participants; very low certainty evidence).

The most commonly reported adverse events associated with methylphenidate were:

• Decreased appetite
• Sleep problems (insomnia, difficulty falling asleep)

The MTA trial reported side effects at endpoint from 245 combined treatment/medication management families:

• 88 (35.9%) reported no side effects
• 122 (49.8%) reported mild side effects only
• 28 (11.4%) reported moderate side effects
• 7 (2.9%) reported severe side effects

The authors note that these figures may overestimate side effects, because 6 of 11 reported severe side effects (depression, worrying, or irritability) could have been due to non-medication factors (MTA Cooperative Group, 1999).

Blinding implications: Decreased appetite and sleep problems are easily recognized by parents and teachers, which compromises blinding in double-blind trials. Active placebos that mimic these effects are rarely used. This means that most "double-blind" trials are effectively unblinded for parents and teachers, which inflates the apparent treatment effect.

4.3 Serious adverse events: very low certainty evidence

The Storebø et al. (2023) Cochrane review found that methylphenidate may not affect serious adverse events (RR 0.80, 95% CI 0.39 to 1.67; 26 trials, 3,673 participants; very low certainty evidence). The trial sequential analysis-adjusted intervention effect was RR 0.91 (95% CI 0.31 to 2.68).

The Storebø et al. (2016) review of non-randomized studies found that in non-comparative cohort studies, the proportion of participants on methylphenidate experiencing any serious adverse event was 1.20% (95% CI 0.70% to 2.00%; 50 studies, 162,422 participants). Withdrawal from methylphenidate due to serious adverse events occurred in 1.20% (95% CI 0.60% to 2.30%; 7 studies, 1,173 participants).

The authors' conclusion: "The findings suggest that methylphenidate administration might lead to serious adverse events, including death, cardiac problems, and psychotic disorders. About 1 in 100 patients treated with methylphenidate seemed to suffer a serious adverse event." However, the certainty of this evidence was rated as very low, and the authors note: "it is not possible to accurately estimate the actual risk of adverse events. It might be higher than reported here."

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Part V — Prevalence and diagnostic thresholds

5.1 Worldwide prevalence: stable when standardized procedures are used

Polanczyk et al. (2007) conducted a systematic review and meta-regression analysis of 102 studies (171,756 subjects from all world regions) reporting point prevalence of ADHD for subjects 18 years or younger according to DSM or ICD criteria.

The worldwide-pooled prevalence was 5.29% (95% CI 5.01–5.56).

However, prevalence estimates varied substantially depending on methodological factors:

• Diagnostic criteria: Studies using DSM-III-R or ICD-10 criteria had significantly lower prevalence than those using DSM-IV criteria.
• Impairment requirement: Studies without a definition of impairment had significantly higher prevalence than those with a definition of impairment.
• Source of information: Studies relying on information from parents, teachers, or "or rule" (parent or teacher) had significantly higher prevalence than those using a best-estimate procedure. Studies using an "and rule" (parent and teacher) had significantly lower prevalence.

Geographic location was not associated with variability in prevalence estimates after accounting for methodological factors.

5.2 No increase over three decades when standardized procedures are used

Polanczyk et al. (2014) updated the two most comprehensive systematic reviews on ADHD prevalence, identifying 154 original studies and including 135 in multivariate analysis. Meta-regression analyses tested the effect of year of study in the context of methodological variables that determine variability in ADHD prevalence.

Key finding: Methodological procedures were significantly associated with heterogeneity of studies. Geographical location and year of study were not associated with variability in ADHD prevalence estimates.

The authors' conclusion: "Confirming previous findings, variability in ADHD prevalence estimates is mostly explained by methodological characteristics of the studies. In the past three decades, there has been no evidence to suggest an increase in the number of children in the community who meet criteria for ADHD when standardized diagnostic procedures are followed."

Thomas et al. (2015) reported a pooled prevalence of 7.2% (95% CI 6.7–7.8) in a meta-analysis of 175 studies including more than 1 million children and adolescents. The prevalence estimate was 2 percentage points lower in studies conducted in Europe compared to North America after adjusting for the edition of diagnostic manual and measurement tools. Salari et al. (2023) reported a prevalence of 7.6% (95% CI 6.1–9.4%) in children aged 3 to 12 years based on 53 studies with 96,907 participants.

5.3 DSM-5 criteria and impairment thresholds

The DSM-5 diagnostic criteria for ADHD require:

• Six or more symptoms of inattention and/or six or more symptoms of hyperactivity-impulsivity (five or more for individuals 17 years or older)
• Symptoms present before age 12 years
• Symptoms present in two or more settings
• Clear evidence that symptoms interfere with or reduce the quality of functioning
• Symptoms not better explained by another mental disorder

The impairment requirement is critical. Studies that do not require evidence of functional impairment report higher prevalence estimates than those that do. The requirement that symptoms be present in two or more settings interacts with the informant agreement problem: if parent and teacher reports disagree, does the child meet criteria?

Different meta-analyses report different pooled prevalence estimates depending on how these methodological factors are handled: 5.29% (Polanczyk et al., 2007), 7.2% (Thomas et al., 2015), and 7.6% in children aged 3–12 years (Salari et al., 2023). The range reflects methodological variance, not changes in underlying prevalence.

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Part VI — What the evidence does not establish

6.1 That stimulants alter the natural course of the disorder

The MTA follow-up data are unambiguous on this point. Original treatment assignment—medication management, behavioral treatment, combined treatment, or community care for 14 months—did not predict outcomes at 6, 8, or 16 years. Early symptom trajectory, regardless of which treatment produced it, predicted long-term outcomes better than treatment type or intensity.

This does not mean stimulants are ineffective. It means their effects are acute, not disease-modifying. Stimulants reduce symptoms while taken, but they do not appear to alter the underlying trajectory of the disorder once discontinued.

6.2 That stimulants improve long-term functional outcomes

The 16-year MTA follow-up found that ADHD-persistent adults had worse educational, occupational, and legal outcomes than the local normative comparison group. But these outcomes were not predicted by original treatment assignment. The type of treatment received in childhood did not determine whether symptoms persisted into adulthood or whether functional outcomes were better or worse.

This is consistent with meta-analyses of academic achievement outcomes. Stimulants improve classroom behavior and on-task attention acutely, but do not consistently improve standardized test scores, grades, or long-term educational attainment. The MTA found that combined treatment showed modest advantages over medication management alone on reading achievement at 14 months, but this advantage did not persist at later follow-ups.

6.3 Which children will respond to stimulants

The MTA titration protocol achieved a 68.5% rate of assignment to a best dose of methylphenidate after double-blind titration. Response rates in the literature typically range from 70% to 80%, but there is no validated algorithm for predicting which children will respond or which dose will be optimal.

Comorbidity, symptom severity, age, sex, and IQ do not reliably predict response. Some children respond robustly to low doses; others require higher doses; some do not respond to methylphenidate but respond to amphetamines; some respond to neither. The only way to determine whether a child will respond is to try the medication and titrate to effect.

6.4 The mechanism by which stimulants work

Stimulants block the reuptake of dopamine and norepinephrine, increasing synaptic availability of these neurotransmitters. The dopamine hypothesis of ADHD proposes that the disorder arises from deficient dopaminergic signaling, particularly in prefrontal-striatal circuits involved in attention, impulse control, and executive function.

But this hypothesis faces the same logical problem as the serotonin hypothesis of depression: the ex juvantibus inference (that a treatment's efficacy validates the disease model it was designed to address) is invalid. Aspirin relieves headaches, but headaches are not caused by aspirin deficiency. Stimulants reduce ADHD symptoms, but this does not prove ADHD is caused by dopamine deficiency.

Additionally, the acute pharmacological effects of stimulants (increased dopamine within hours) do not match the time course of symptom improvement (which is also rapid). This is different from antidepressants, where the mismatch between acute serotonin effects (hours) and clinical improvement (weeks) has driven research into downstream neuroplastic mechanisms. For stimulants, the symptom improvement is rapid, which is consistent with an acute symptomatic effect rather than a disease-modifying mechanism.

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Part VII — The two overclaims, and what replaces them

7.1 The invalidation narrative: "ADHD is not real"

The claim: ADHD is not a real disorder but a medicalization of normal childhood behavior, driven by pharmaceutical marketing and societal intolerance of active children. Stimulants are prescribed to make children docile and compliant, not to treat a medical condition.

What the evidence shows: ADHD symptoms cluster consistently across cultures and diagnostic systems. Children who meet diagnostic criteria show significant functional impairment in academic, social, and family domains. Stimulants reduce symptoms acutely compared to placebo with effect sizes in the medium-to-large range (SMD −0.74 to −1.02, depending on rater). These benefits are real, not placebo effects.

The prevalence of ADHD has not increased when standardized diagnostic procedures are followed, which contradicts the narrative that diagnostic expansion is driven by lowering thresholds. Variability in prevalence estimates is explained by methodological factors (diagnostic criteria, impairment requirements, informant rules), not by changes in underlying rates.

What survives: ADHD symptoms are dimensionally distributed. The boundary between "clinical" and "subclinical" ADHD is set by diagnostic thresholds (six symptoms vs five; impairment requirement vs none; "and" rule vs "or" rule), not by natural discontinuities. This means diagnostic practice matters, and changes in diagnostic criteria, informant rules, or impairment thresholds will change prevalence estimates. But this does not mean the symptoms are not real or that they do not cause impairment.

7.2 The neurobiological-deficit story: "Stimulants fix the brain"

The claim: ADHD is a discrete brain disorder caused by dopamine deficiency. Stimulants correct this deficiency, improving not just symptoms but long-term functional outcomes. Early treatment alters the natural course of the disorder.

What the evidence shows: Stimulants reduce symptoms acutely, but the benefits do not compound over time or translate into improved long-term functional outcomes. The MTA found that original treatment assignment did not predict outcomes at 6, 8, or 16 years. Early symptom trajectory—reflecting a combination of treatment response, baseline severity, and sociodemographic factors—predicted outcomes better than treatment type or cumulative medication exposure.

Extended stimulant use was associated with height suppression but not with reduction in symptom severity in young adulthood. The mechanism by which stimulants work is not fully understood, and the dopamine-deficiency hypothesis faces the same logical problem as the serotonin hypothesis in depression.

What survives: Stimulants are effective symptomatic treatments. They reduce inattention, hyperactivity, and impulsivity while taken, allowing children to function better in the short term. For some children, this symptomatic relief may be substantial and clinically meaningful. For others, the benefits are modest or offset by adverse effects. The decision to use stimulants involves weighing acute symptomatic benefits against adverse effects (decreased appetite, sleep problems, cardiovascular changes, height suppression) and recognizing that these are symptomatic treatments, not disease-modifying interventions.

7.3 The version that survives

ADHD symptoms are real, dimensionally distributed, and context-dependent. Children who meet diagnostic criteria show functional impairment in multiple domains. Parent-teacher rating disagreement is not measurement error; it reflects situation-specific behavior across home and school settings. Diagnostic prevalence is stable when standardized procedures are used, but the boundary between clinical and subclinical ADHD is set by diagnostic thresholds, not by natural discontinuities.

Stimulants reduce symptoms acutely, with effect sizes that vary by rater. Teacher-rated symptom reduction (SMD −0.74) is similar to clinician-rated reduction (SMD −0.78 to −1.02), but parent ratings are often lower, and informant disagreement is substantial. The certainty of this evidence is very low due to short trial duration, high risk of bias, and compromised blinding.

The 14-month MTA advantage disappeared by 36 months, and original treatment assignment did not predict outcomes 6–16 years later. Type or intensity of treatment in childhood did not determine symptom persistence or functional outcomes in adolescence or adulthood. Early symptom trajectory—regardless of which treatment produced it—predicted long-term outcomes better than treatment type.

Extended stimulant use is associated with height suppression but not with long-term symptom reduction or improved functional outcomes. The reduction in adult height (2.55–4.06 cm for consistent use vs negligible use) is statistically significant and clinically measurable, but the clinical significance of this height difference is debated.

Stimulants are symptomatic treatments, not disease-modifying interventions. They reduce symptoms while taken, but do not alter the natural course of the disorder once discontinued. The decision to use stimulants involves weighing acute symptomatic benefits against adverse effects and recognizing that these benefits do not compound over time or translate into improved long-term functional outcomes.

What the evidence establishes: Stimulants reduce ADHD symptoms acutely compared to placebo, with moderate-to-large effect sizes on teacher and clinician ratings. The 14-month MTA trial found medication management superior to behavioral treatment for core ADHD symptoms, but this advantage disappeared by 36 months, and original treatment assignment did not predict outcomes 6–16 years later. Extended stimulant use is associated with height suppression and small increases in blood pressure and heart rate. The certainty of evidence is very low, most trials are short-term, and blinding is compromised by easily recognized side effects.

What it does not establish: That ADHD arises from a correctable neurotransmitter deficit, that stimulants alter the natural course of the disorder or improve long-term functional outcomes, which children will respond to stimulants, or that parent-teacher disagreement reflects unreliable measurement rather than situation-specific behavior.

The structural problem: Most trials are short-term, unblinded in practice, and the evidence certainty is very low. The MTA—the longest and most carefully conducted trial—showed that treatment benefits did not persist after the randomized phase ended, and early symptom trajectory predicted long-term outcomes better than treatment type. Stimulants provide acute symptomatic relief, but the benefits do not compound over time, and the inference from acute symptom reduction to long-term functional benefit is not supported by the data.

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References

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Cortese, S. et al. (2018). "Comparative efficacy and tolerability of medications for attention-deficit hyperactivity disorder in children, adolescents, and adults: a systematic review and network meta-analysis." The Lancet Psychiatry, 5(9), 727–738.

Gomez, R. (2019). "Is the endorsement of the Attention Deficit Hyperactivity Disorder symptom criteria ratings influenced by informant assessment, gender, age, and co-occurring disorders? A measurement invariance study." International Journal of Methods in Psychiatric Research, 28(3), e1794.

Hechtman, L. et al. (2016). "Functional Adult Outcomes 16 Years After Childhood Diagnosis of Attention-Deficit/Hyperactivity Disorder: MTA Results." Journal of the American Academy of Child & Adolescent Psychiatry, 55(11), 945–952.

Jensen, P. S. et al. (2007). "3-year follow-up of the NIMH MTA study." Journal of the American Academy of Child & Adolescent Psychiatry, 46(8), 989–1002.

Liang, E. F. et al. (2018). "Cardiovascular Effects of Stimulant and Non-Stimulant Medication for Children and Adolescents with ADHD: A Systematic Review and Meta-Analysis of Trials of Methylphenidate, Amphetamines and Atomoxetine." CNS Drugs, 32(3), 199–214.

Molina, B. S. G. et al. (2009). "The MTA at 8 years: prospective follow-up of children treated for combined-type ADHD in a multisite study." Journal of the American Academy of Child & Adolescent Psychiatry, 48(5), 484–500.

MTA Cooperative Group. (1999). "A 14-month randomized clinical trial of treatment strategies for attention-deficit/hyperactivity disorder." Archives of General Psychiatry, 56(12), 1073–1086.

Polanczyk, G. et al. (2007). "The Worldwide Prevalence of ADHD: A Systematic Review and Metaregression Analysis." American Journal of Psychiatry, 164(6), 942–948.

Polanczyk, G. V. et al. (2014). "ADHD prevalence estimates across three decades: an updated systematic review and meta-regression analysis." International Journal of Epidemiology, 43(2), 434–442.

Salari, N. et al. (2023). "The global prevalence of ADHD in children and adolescents: a systematic review and meta-analysis." Italian Journal of Pediatrics, 49, 48.

Storebø, O. J. et al. (2016). "Methylphenidate for attention deficit hyperactivity disorder (ADHD) in children and adolescents – assessment of adverse events in non-randomised studies." Cochrane Database of Systematic Reviews, 2016(5), CD012069.

Storebø, O. J. et al. (2023). "Methylphenidate for children and adolescents with attention deficit hyperactivity disorder (ADHD)." Cochrane Database of Systematic Reviews, 2023(3), CD009885.

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Appendix: What this review corrected

Four claims in the initial version required correction after citation integrity review:

1. Storebø et al. (2023) risk of bias ratings: The initial version incorrectly stated "9% of trials were high risk of bias, 73% moderate, 18% low" (these figures were from Cipriani 2018 on depression). Primary-source verification confirms that of 212 trials, 191 were assessed at high risk of bias and 21 at low risk. If deblinding of methylphenidate due to typical adverse events is considered, then all 212 trials were at high risk of bias. Mean trial duration was 28.8 days (range 1–425 days). Corrected in executive summary point 6, "How to read this review," section 2.1, and closing section.

2. Height suppression: Swanson 2017 vs 2019: The initial version mixed two papers. Swanson et al. (2017) Journal of Child Psychology and Psychiatry reports endpoint comparisons: ADHD vs LNCG 1.29 ± 0.55 cm; consistent-or-inconsistent vs negligible 2.55 ± 0.73 cm (d = 0.42); consistent vs inconsistent 2.36 ± 1.13 cm (d = 0.38). Swanson et al. (2019) Journal of the American Academy of Child & Adolescent Psychiatry reports trajectory analyses with z-scores: consistent vs negligible −0.66 z / −4.06 cm; consistent vs inconsistent −0.45 z / −2.74 cm; consistent vs LNCG −0.54 z / −3.34 cm. Section 3.1 now distinguishes both papers and ties each number to its source.

3. Prevalence meta-analysis author: The initial version cited "Kazda et al. 2023" for the 7.6% prevalence in children under 12. The correct citation is Salari et al. (2023), Italian Journal of Pediatrics, 53 studies, 7.6% (95% CI 6.1–9.4%) in children aged 3–12 years. Corrected in section 5.2 and references.

4. Executive summary height comparison: The initial version stated "consistent vs negligible use" for the 2.55 cm figure, which was imprecise for the Swanson 2017 paper. Corrected to "consistent-or-inconsistent vs negligible" to match the actual comparison group tested.