AIM: To test the efficacy and safety of osmotic release oral system (OROS) methylphenidate (MPH) in doses up to 180 mg/day to treat attention deficit hyperactivity disorder (ADHD) and prevent any drug relapse in individuals with a co-diagnosis of ADHD and amphetamine dependence.

DESIGN: Randomized placebo-controlled 24-week double-blind trial with parallel groups design.

SETTING: Participants were recruited from medium security prisons in Sweden. The medication started within 2 weeks before release from prison and continued in out-patient care with twice-weekly visits, including once-weekly cognitive behavioural therapy.

PARTICIPANTS: Fifty-four men with a mean age of 42 years, currently incarcerated, meeting DSM-IV criteria for ADHD and amphetamine dependence.

MEASUREMENTS: Change in self-reported ADHD symptoms, relapse to any drug use (amphetamine and other drugs) measured by urine toxicology, retention to treatment, craving and time to relapse.

FINDINGS: The MPH-treated group reduced their ADHD symptoms during the trial (P = 0.011) and had a significantly higher proportion of drug-negative urines compared with the placebo group (P = 0.047), including more amphetamine-negative urines (P = 0.019) and better retention to treatment (P = 0.032).

CONCLUSIONS: Methylphenidate treatment reduces attention deficit hyperactivity disorder symptoms and the risk for relapse to substance use in criminal offenders with attention deficit hyperactivity disorder and substance dependence.