Cannabis After Psychosis: Relapse Risk and What Was Observed After Quitting

About a third of people are using cannabis when they have a first episode of psychosis. A meta-analysis estimated the prevalence at 33.7% (35 samples; 95% CI 31% to 39%, as printed).¹ In a review of studies that followed substance use, primarily cannabis and alcohol, after a first episode, approximately half of patients became abstinent or significantly reduced their alcohol and drug use.²

Relapse outcomes differed between people who continued and people who stopped. In a 2016 meta-analysis of 24 studies and 16,565 participants, continued cannabis users had more relapse than people who stopped, and people who stopped did not differ from non-users (d=0.02, p=0.82).³ Whether cannabis causes psychosis in the first place is a separate question, covered on the page about cannabis and psychosis.

Continued cannabis use is associated with more relapse

The meta-analysis results are Cohen's d values, a standardized difference between groups, and the abstract reports no relapse percentages for each group.³

• Continued users compared with non-users: d=0.36 (95% CI 0.22 to 0.50) for relapse
• Continued users compared with people who stopped: d=0.28 (95% CI 0.12 to 0.44)
• People who stopped compared with non-users: d=0.02 (95% CI -0.12 to 0.15)

What the within-person analysis adds

A study of 220 people with first-episode psychosis in South London, followed for at least 2 years, compared periods of cannabis use with periods of no use. The odds of relapse, defined as hospitalization for psychosis, were higher during periods of use (odds ratio 1.13, 95% CI 1.03 to 1.24).⁵

In a cross-lagged analysis, cannabis use was associated with later relapse (β=0.44, P=.04), while relapse was not associated with later cannabis use (β=-0.29, P=.59). The authors concluded that the association is unlikely to be a result of self-medication or of genetic and environmental confounding. The odds ratio is small, and the study is observational.⁵

Medication adherence may account for part of the association

In a meta-analysis of 15 observational studies, cannabis users had higher odds of non-adherence than non-users (odds ratio 2.46). At follow-up, former users did not differ from non-users (odds ratio 1.12).⁶

In a London cohort of 245 people followed for 2 years after a first episode, medication adherence partly mediated the association between continued cannabis use and risk of relapse, with a proportion mediated of 26%. Across outcomes, the authors estimated that between 20% and 36% might be mediated through adherence.⁴ Anyone using cannabis while taking an antipsychotic should tell the prescriber, who can plan around it.

Daily high-potency use had the worst outcome

A London study of 256 people who presented with a first episode between 2002 and 2013 compared types of use. People who used high-potency, skunk-like cannabis daily in all 24 months of follow-up had the worst outcome, with higher odds of relapse, defined as a later hospital admission (odds ratio 3.28, 95% CI 1.22 to 9.18). The abstract does not state the comparison group.⁷

What was observed in people who stopped

In a study of 92 people followed for 8 years after a first admission, 27 stopped cannabis, 25 continued, and 40 had never used. The groups did not differ significantly in the short term. In the long term, those who stopped had better functional outcome than the other two groups (effect size 1.26) and fewer negative symptoms than those who continued.⁸

None of the studies cited here randomized people to stop, and people who stop may differ from people who continue.

One cohort found no association with relapse

A study of 110 people in early psychosis with cannabis abuse or dependence, assessed four times over 18 months, found "no evidence of a specific association between cannabis use and positive symptoms, or negative symptoms, relapse or hospital admissions."⁹ An earlier systematic review of 13 longitudinal studies reported that few adjusted for baseline illness severity, that adjustment often attenuated the results substantially, and that confidence that most associations were specifically due to cannabis was low.¹⁰

Treatment trials did not lower relapse or admissions

In 110 people with problematic cannabis use after a first episode, motivational interviewing with cognitive behavioral therapy, in a brief or a long format, conferred no benefit over standard care on the frequency or amount of cannabis use, and did not improve symptoms, hospital admissions, or relapse.¹¹ The CIRCLE trial randomized 551 people aged 18 to 36, who'd had at least one episode of psychosis and reported recent cannabis use, to 12 weeks of voucher rewards plus psychoeducation or to psychoeducation alone. Time to acute psychiatric care did not differ (hazard ratio 1.03, 95% CI 0.76 to 1.40), and by 18 months 33% and 30% had been admitted to an acute psychiatric service at least once.¹²

The MIDAS trial enrolled a different population: 327 people with schizophrenia, schizophreniform disorder, or schizoaffective disorder and dependence on or misuse of drugs, alcohol, or both. It wasn't limited to cannabis or to a first episode. Therapy had no beneficial effect on hospital admission or death (23.3% versus 20.2%) and no effect on the frequency of substance use, though it had a statistically significant effect on the amount used per substance-using day.¹³

Two cannabidiol trials had different results

In an exploratory trial of 88 patients, those who received cannabidiol (CBD) 1000 mg/day for 6 weeks alongside their antipsychotic had lower levels of positive symptoms than the placebo group (PANSS treatment difference -1.4, 95% CI -2.5 to -0.2).¹⁴ In a 6-week trial of 36 stable outpatients with chronic schizophrenia, 600 mg/day was not associated with improvement in cognition or PANSS scores, and sedation was more prevalent with CBD.¹⁵

Both trials added CBD to existing antipsychotic treatment, and neither tested it as a replacement. In a 2025 crossover trial of 30 people with schizophrenia or schizoaffective disorder and cannabis use disorder, CBD taken before inhaled cannabis did not attenuate the acute effects on psychotic symptoms and appeared to exacerbate them.¹⁶ Adding CBD is a question for the prescriber.

Limitations of the evidence

This evidence has limitations. First, the relapse findings are observational, and none of the studies cited here randomized people to stop. Second, three of the analyses recruited first-episode patients in South London over the same dates, 2002 to 2013. Nevertheless, the meta-analysis of 24 studies found that continued use was associated with more relapse and that people who stopped did not differ from non-users.^{3, 5, 7, 4}

Although these studies can't show that stopping prevents relapse, the outcomes observed in people who stopped are a reason to raise current cannabis use with the psychiatrist and to make it part of relapse planning.

In a crisis: call or text 988, or go to the nearest emergency department. A first episode of psychosis belongs in a hospital-based or coordinated specialty care program.

I start and manage clozapine in an outpatient practice in Chelsea, Manhattan. Details are on the schizophrenia care in NYC page. Clozapine should not be stopped, skipped, or restarted without the prescriber. This page is general information and does not replace an evaluation.

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