Cannabis users who experienced a psychosis are particularly vulnerable to cannabis-related harms, which can include worse psychotic symptoms and more hospitalizations. Unfortunately, few psychosocial interventions exist that aim to decrease these harms. Instead, most focus on ceasing cannabis use which is rarely appealing to cannabis users. Furthermore, face-to-face psychotherapy often remains inaccessible to people with psychosis mostly due to lack of trained clinicians. Alternatives such as e-interventions have the potential to increase access to treatment and decrease clinicians' workload. Among cannabis harm reduction approaches are the protective behavioural strategies. These strategies do not encourage nor discourage cannabis use. Instead, they recommend behaviours for safer cannabis use. For example, these strategies include: 1) avoid driving a car under the influence of cannabis, 2) avoid mixing cannabis with other drugs and 3) purchase cannabis only from a trusted source. In the present pan-Canadian study, we will test the first e-intervention called CHAMPS (Cannabis Harm-reducing App for Managing Practices Safely) for cannabis harm reduction adapted for young adult cannabis users who experienced a psychosis. CHAMPS is a smartphone application that includes 17 strategies for safer cannabis use, a personalized consumption goal and a consumption journal. The goals of this study are 1) to confirm whether CHAMPS is acceptable to participants and 2) to test whether it works, notably by positively impacting participants' health and cannabis consumption habits.

This multicentric, two-arm, open-labelled, pilot randomized controlled trial involves 100 young cannabis users who experienced a psychosis and are followed in an early intervention service (EIS) in Canada. Participants will be randomized in a 1:1 ratio to one of two interventions:

• CHAMPS and EIS
• EIS alone

The smartphone application CHAMPS contains six modules (each lasting 15-20 min, weeks 1 to 6) and a booster session (20 min, week 10) based on motivational interviewing and harm reduction approaches. EIS consists of standard of care and psychoeducation material on cannabis use offered in first episode psychosis clinics and administered through in-person visits and/or phone or video calls.

All participants will be assessed for a follow-up at weeks 6, 12 and 18. Data on mental health, substance use, cannabis dependence severity, cannabis-related problems, quality of life and health care service utilization will be obtained through questionnaires and medical charts.

Participants must meet all following inclusion criteria:

• diagnosed with any psychotic disorder, which can include schizophrenia, schizoaffective disorder, bipolar disorder with psychotic features, delusional disorder, psychotic disorder not otherwise specified, brief psychotic disorder and substance-induced psychotic disorder;
• has been followed at an early psychosis clinic for a minimum of 3 months;
• currently using cannabis (at least one time in the past 4 weeks);
• is open to changing cannabis-related practices;
• able to provide full informed consent;
• available for the whole study duration and able to comply with study procedures;
• able to comprehend French or English.

Participants are excluded if any of these exclusion criteria is met:

• pregnancy, nursing or any medical condition that in the opinion of the psychiatrist precludes safe participation in the study or the ability to provide fully informed consent;
• any disabling, unstable or acute mental condition that in the opinion of the psychiatrist precludes safe participation in the study or the ability to provide fully informed consent;
• any legal/judicial status/issue, pending legal action, or other reasons in the opinion of the study team that might prevent completion of the study;
• presence of a substance use disorder that, in the opinion of the psychiatrist, precludes safe participation in the study (e.g., very unstable or severe substance use disorder);
• currently seeking psychological or pharmacological treatment for cannabis use disorder to cease or decrease his/her use;
• currently participating in another specific cannabis-focused intervention.

Group assignment will not be masked after randomization, but it will be at the data analysis stage.