Lijffijt 2006.

Study characteristics
Methods	3‐week, randomised, double‐blind, cross‐over, within‐participant trial conducted to test MPH/placebo to assess correlations between measures of attention and inhibition with dopamine and norepinephrine blood levels: MPH placebo
Participants	Number of participants screened: not stated Number of participants included: 15 (13 boys, 2 girls) Number of participants followed up: 15 Number of withdrawals: 0 Diagnosis of ADHD: DSM‐IV (combined (11), hyperactive‐impulsive (2), inattentive (2)) Age: mean 10.74 years (range 7‐13) IQ: mean 97.60 MPH‐naive: 0% Ethnicity: not stated Country: the Netherlands Setting: outpatient clinic Comorbidity: anxiety (n = 6), ODD (n = 5) Comedication: not stated Other sociodemographics: none Inclusion criteria ADHD diagnosis according to DSM‐IV Participants familiar with intake of MPH for at least a year Exclusion criteria None stated
Interventions	Participants were randomly assigned to different possible drug condition orders of 0.5 mg/kg or 1.0 mg/kg MPH and placebo Mean MPH dosage: 22.67 mg Administration schedule: not stated Duration of each medication condition: 1 day Washout before trial initiation: 24 h before testing Medication‐free period between interventions: no Titration period: none/duration Treatment compliance: not stated
Outcomes	ADHD symptoms CPRS CTRS General behaviour CBCL; Teachers' Report Form Non‐serious AEs Paper mentioned only this: "Although side effects were minimal (a feeling of sleepiness), four participants were too fatigued after placebo or the 1.0 mg/kg dose to continue with the change task after they first completed the stop task"
Notes	Sample calculation: no Ethics approval: yes; "The study was approved by the national medical ethical committee (CCMO)" Key conclusion of trial authors In children with ADHD, MPH could act primarily on inhibitory control and is not influenced by task difficulty Exclusion of MPH non‐responders/children who have previously experienced AEs while taking MPH before randomisation: yes, see inclusion criteria Any withdrawals due to AEs: yes, "four participants were too fatigued after placebo or the 1.0 mg/kg dose to continue with the change task after they first completed the stop task" Funding source: not declared Email correspondence with trial authors: March 2014: we sent an email to the trial author to request additional information but have received no reply.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised
Allocation concealment (selection bias)	Unclear risk	No information
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Double‐blind
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Double‐blind
Incomplete outcome data (attrition bias) All outcomes	Low risk	No dropouts. "All participants were familiar with the intake of MPH for at least 1 year" Selection bias (e.g. titration after randomisation → exclusion of methylphenidate non‐responders or placebo responders): no
Selective reporting (reporting bias)	Unclear risk	No protocol available