Johnson 2013.

Methods	A cohort stud of methylphenidate use for 6 weeks
Participants	Number of participants screened: not stated Number of participants included: 96 Number of participants followed up: 77 Number of withdrawals: 9 Diagnosis of ADHD: DSM‐IV (subtype: combined (82%), hyperactive‐impulsive (9%), inattentive (9%)) Age: mean 8 (SD 2.6) years (range 4‐15) IQ: mean 92.7 (SD 15.9) Sex: 66 males, 11 females Methylphenidate‐naïve: 100% Ethnicity: not stated Country: Ireland Comorbidity: oppositional defiant disorder: 60%, conduct disorder: 16% Comedication: paracetamol, salbutamol and steroid inhalers for asthma and ampicillin antibiotics Sociodemographics: not stated Inclusion criteria: Between 4 and 15 years of age Meet DSM‐IV criteria for ADHD Be stimulant naïve Be willing to provide a blood or saliva sample for genetic analysis Exclusion criteria: IQ < 70 Epilepsy, fragile X syndrome, fetal alcohol syndrome, maternal drug abuse during pregnancy, primary diagnosis of pervasive developmental disorder or bipolar disorder Current treatment with non‐stimulant psychotropic medications
Interventions	Methylphenidate type: 45 participants took short‐acting methylphenidate. Otherwise not stated Methylphenidate dosage: mean 0.57 mg/kg/day (SD 0.19) Administration schedule: not stated Time points: not stated Duration of intervention: 1 year, however only data up to 6 weeks were reported here Treatment compliance: not stated
Outcomes	Non‐serious adverse events: Barkley's Side Effect Rating Scale at 6 weeks, parent rated ‐ included decreased appetite, weight loss, headache, abdominal pain, irritability, sadness, insomnia, and tics
Notes	Sample calculation: not stated Any withdrawals due to adverse events: not stated Ethics approval: granted by 8 local research ethics committees Funding/vested interests: this study was funded by the Irish Health Research Board, Dublin Authors stated that there were no competing financial interests Key conclusions of the study authors: the study found an association between 2 CES1 SNP markers and sadness as a side effect of short‐acting methylphenidate Comments from the study authors: limitations: not cross‐over design; serum measures of methylphenidate were not obtained; study did not consider environmental factors impacting on CES1A1 function Exclusion of methylphenidate non‐responders/children who have previously experienced adverse events on methylphenidate: no