Numbers of participants who are referred, screened, eligible, consenting, randomized, initiating and completing the study

Frequency and quantity of cannabis use in the last 14 days will be measured using the Timeline Follow Back (TLFB) which is a tool that captures self-reported drug use. The TLFB will assess the frequency of cannabis use, the self-reported days with abstinence from cannabis weekly, as well as type of cannabis products, quantity and dose/concentration in cannabinoids.

Cannabis-related physical, psychological, social, and functioning problems will be assessed with the Marijuana Problems Scale (MPS), which is a 19-item self-report instrument that measures change in problems related to cannabis use over time. The scale contains 19 items that represent potential negative effects of marijuana on social relationships, self-esteem, motivation and productivity, work and finances, physical health, memory impairment, and legal problems. For each item, the participant reports problems related to cannabis use in the last month by choosing one of the following three options: 0=not a problem, 1=a minor problem, 2=a serious problem. A total score is calculated, and higher scores indicate more serious problems with cannabis use.

The frequency of cannabis use (number of days in the previous 14 days weeks) and rates of point prevalence for cannabis abstinence will be assessed with the Timeline Followback (TLFB). The TLFB is a tool that captures self-reported drug use. The TLFB will assess the frequency of cannabis use, the self-reported days with abstinence from cannabis weekly, as well as type of cannabis products, quantity and dose/concentration in cannabinoids.

Past two weeks other drug use according to the Timeline Follow-Back Questionnaire (TLFB) which is a tool that captures self-reported drug use in the past 14 days. The TLFB will assess the frequency of drug use, and capture self-reported days with abstinence from substance use.

Severity of cannabis dependence will be measured with the self-administered, the Severity of Dependence Scale (SDS). The SDS contains five items that measure the psychological components of dependence including control over cannabis use, anxiety over missing a dose, worry related to use, desire to stop and difficulties related to stopping using cannabis. Each item is score on a four-point scale (0=never/almost never, 1=sometimes, 2=often, 3=always/nearly always). A total score is calculated, and higher scores indicate higher levels of dependence.

Measured with the self-administered 17-item Protective Behavioral Strategies-Marijuana (PBSM) questionnaire. The PBSM will be used to measure cannabis-related harms in the last 30 days by asking participants to rate on a six-point scale their behaviors (e.g., Avoid using before work or school) related to cannabis use (1=never, 2=rarely, 3=occasionally, 4=sometimes, 5=usually and 6=always). Mean scores will be calculated with higher scores indicating higher risk behaviors.

Participant confidence in resisting cannabis use will be measured using the Drug-Taking Confidence Questionnaire (DTCQ), which is an 8-item instrument that has shown reliability and validity in measuring coping self-efficacy. Participants will rate on a 6-point scale (0= not at all confident, 20=20% confident, 40=40%, 60=60% confident, 80=80% confident; and 100=very confident) their confidence to resist cannabis use (i.e., "I would be able to resist the urge to use cannabis…" in 8 different situations e.g. "…. If other people treated me unfairly or interfered with my plans". Participant's confidence in his/her ability to resist cannabis use will be evaluated by calculating a mean score e.g., a confidence score between 0% to 20% reflects little or no confidence at all.

The impact of psychosis and CUD on participants' life, we will be measured using the Satisfaction with Life questionnaire (SWL), which is a self-report, 18-item scale that has been validated in participants with schizophrenia and schizophrenia-related disorders. The SWL assesses individual's satisfaction with life pertaining to four domains: living situation (4 items, e.g., "How much do you like the place where you live?"), social relationships (6 items, e.g., How satisfied are you with the number of friends you have?"), work (2 items, e.g., "How satisfied are you with the kind of work that you do?") and self and present life (6 items, e.g., "How satisfied are you with yourself on the whole?"). Items are measured on a five-point Likert scale from "not at all satisfied" to "very satisfied". For each domain a mean score is calculated, and higher scores are indicative of greater satisfaction.

Health service utilization information including number of days of hospitalizations and number of emergency visits in the past 30 days will be collected via self-report from the participant and can be confirmed as needed through the patient medical record abstraction and contact with the case manager.

To capture participants' decision stage of change related to decreasing or stopping cannabis abstinence, we will use the Precaution Adoption Model (PAPM). The PAPM consists of 7 distinct stages of health decision-making: 1) unaware of the health behavior, 2) unengaged in the decision, 3) undecided, 4) decided not to act, 5) decided to act, 6) acting and 7) maintenance. Participants will select one of 6 response options corresponding to PAPM stages 2 to 7: "At this moment, I have not thought about decreasing or stopping using cannabis", "At this moment, I am undecided about decreasing or stopping using cannabis", At this moment I do not want to decrease or stop using cannabis", "At this moment I do want to decrease or stop using cannabis", "I have recently decreased or stopped using cannabis" and "I decreased or stopped using cannabis more than one month ago".

The availability of social support will be measured with the short form of the Social Provisions Scale (SPS-10) that consists of 2 items per dimension of support (i.e., emotional support or attachment, social integration, reassurance of worth, tangible help, orientation) for a total of 10 items. Items are measured on a four-point Likert scale from "1-totally disagree" to "4-totally agree" and a total score will be calculated. A continuous scale score is computed by summing responses to the 10 questions, with values ranging from 10 to 40. The SPS-10 summary score is not computed for respondents with data missing on any items. Higher scores can be interpreted as having higher levels of social support.