Akhondzadeh 2004.

Methods	A 6‐week double‐blind, placebo‐controlled, parallel group trial with 2 interventions: Methylphenidate + zinc sulfate Methylphenidate + placebo
Participants	Number of participants screened: not stated Number of participants included: 22 Number of participants followed up: 20 Number of withdrawals: 2 Diagnosis of ADHD: DSM‐IV (subtype: combined (100%)) Age: mean: 7.73 (1.63), range: 5‐11 IQ: > 70 Sex: 12 males, 10 females Methylphenidate‐naïve: 100% Ethnicity: Persian Country: Iran Setting: outpatient clinic Comorbidity: not stated Comedication: not stated Sociodemographics: not stated Exclusion criteria Previously diagnosed with a psychiatric disorder Mental retardation (IQ < 70) Clinically significant chronic medical condition, including a past history of cardiovascular disease, organic brain disorder, seizures, current abuse or dependence on drugs within 6 months Current treatment with psychotropic medications
Interventions	Methylphenidate type: not stated Methylphenidate dosage: 1 mg/kg/day (+ placebo: sucrose, 55 mg) Administration schedule: twice daily, 7 am and 3 pm Duration of each medication condition: 6 weeks Treatment compliance: not stated
Outcomes	Systematically recorded throughout the study and were assessed using a checklist administered by a resident of psychiatry on days 7, 14, 21, 28 and 42 Non‐serious adverse events: Anxiety: 3 Decreased appetite: 7 Difficulty falling asleep: 6 Abdominal pain: 4 Nausea: 3 Headache: 9 Metallic taste: 0
Notes	Sample calculation: not stated Any withdrawals due to adverse events: none Ethics approval: not explicitly stated but inferred: informed consent (parent and children) was received before the administration of any study procedure or dispensing of study medication in accordance with the ethical standards of the investigative site's institutional review board and with the Helsinki Declaration of 1975, as revised in 2000 Funding/vested interests/authors' affiliations: not stated Key conclusions from study authors: this double‐blind, placebo‐controlled study demonstrated that zinc as a supplementary medication might be beneficial in the treat‐ ment of children with ADHD. However, further investigations and different doses of zinc are required to replicate these findings in children with ADHD. Comments from the study authors: the limitations of the present study, including lack of a full placebo group, using only a moderate dose of methylphenidate, the small number of participants, short period of follow‐up and lack of plasma zinc concentration should be considered so further research in this area is needed Exclusion of methylphenidate non‐responders/children who have previously experienced adverse events on methylphenidate: no