Few randomised controlled trials have been aimed specifically at substance use reduction among people with psychotic disorders.

To investigate whether a 10-session intervention consisting of motivational interviewing and cognitive-behavioural therapy (CBT) was more efficacious than routine treatment in reducing substance use and improving symptomatology and general functioning.

A community sample of people with a psychotic disorder and who reported hazardous alcohol, cannabis and/or amphetamine use during the preceding month was recruited. Participants were randomly allocated to motivational interviewing/CBT (n=65) or treatment as usual (n=65), and were assessed on multiple outcomes at baseline, 15 weeks, 6 months and 12 months.

There was a short-term improvement in depression and a similar trend with regard to cannabis use among participants who received the motivational interviewing/CBT intervention, together with effects on general functioning at 12 months. There was no differential benefit of the intervention on substance use at 12 months, except for a potentially clinically important effect on amphetamine use.

The motivational interviewing/CBT intervention was associated with modest improvements.