Skip to main content Skip to navigation

The CIRCLE Study


A study into Cannabis and Psychosis by Dr Steven Marwaha and Melanie Gibbs

Can cannabis use be controlled through incentives and rewards?

The CIRCLE trial is a randomised controlled trial of contingency management for reducing cannabis use in psychosis. Specifically, testing whether rewarding abstinence from cannabis using shopping vouchers is cost-effective.

The trials recruit solely from EI services, so are focusing on people aged 18-35 that have a history of problematic cannabis use. They are randomised to one of two groups: the experimental or control group.

The Experimental Group
In the experimental group, participants are offered 12 weeks of contingency management. Each week they attend, whether they have used cannabis in the previous week is tested using urinalysis. If they have been abstinent, they receive a shopping voucher for supermarkets Asda or Tesco.

Participants are also offered 6 x 30 min psycho-education sessions about the relationship between cannabis and psychosis – this is meant to be equivalent to treatment as usual.

The Control Group
The control group is offered the psycho-education only.

The project began in 2012 and is set to continue until 2017.