Schizophrenia onset. Marijuana users who suffer a drug-induced psychosis are at very high risk of developing a psychotic illness later on. A ≥3-year follow-up study18 of 535 patients who had not been treated for psychotic problems before being diagnosed with marijuana-induced psychotic symptoms found that:
- marijuana-induced psychotic episodes often remitted quickly with minimal treatment
- about one-half of patients were diagnosed with a schizophrenia-spectrum disorder (mostly paranoid schizophrenia) at follow up
- the gap between the marijuana-induced episode and diagnosis of a schizophrenia-spectrum disorder was >1 year in 47% of cases.
- the first episode of schizophrenia in these patients occurred several years earlier than in schizophrenia patients without marijuana-induced psychosis.
Although these findings require replication, they challenge the belief that marijuana-induced psychosis is benign (Box 3).
Implications for treatment
Most psychiatric practitioners treat patients who have psychotic illness and use marijuana (Box 4). Compared with nonusers, these patients tend to have:
- earlier age of schizophrenia onset
- more psychotic symptoms
- worse prognosis because of poorer treatment adherence
- increased symptom severity and persistence
- higher relapse rates.19
Therefore, ask patients with psychotic disorders about their marijuana use, and treat both the marijuana use and the psychosis. Evidence to guide treatment is scarce, however. Nicotine, marijuana, and alcohol use are often intertwined. This suggests that treatments that target a variety of substances may be more efficient than targeted ones, even if the generic interventions are brief.20
A study of marijuana users with early psychosis showed, for example, that marijuana-focused treatment was not more effective than psychoeducation, although both resulted in reduced use.21 In nonpsychotic individuals, giving 90 adult patients incentive vouchers to exchange for retail items each time they provided a marijuana-negative urine specimen resulted in increased abstinence rates over a 12-month period (Box 5).22,23 Cognitive-behavioral therapy helped to sustain the vouchers’ positive effect on abstinence after the initial 14-week treatment.23
Voucher-based reinforcement: Stay clean, earn free movie passes
Efficacy. In voucher-based reinforcement therapy, patients receive vouchers or monetary incentives redeemable for goods and services, contingent on satisfying predetermined therapeutic goals. A meta-analysis22 showed this therapy model can produce better outcomes in substance use disorders, compared with control treatment.
Marijuana abstinence. A 12-month study of 90 cannabis-dependent adults23 found that voucher-based reinforcement therapy could extend marijuana abstinence. During the 14 weeks of active treatment, participants could redeem vouchers for goods or services—such as movie passes, sports/hobby equipment, work materials, or vocational classes.
- Participants earned a voucher worth $1.50 for the first negative specimen.
- Voucher values increased by $1.50 for each consecutive negative specimen.
- Two consecutive negative specimens earned a $10 bonus.
- Voucher values dropped back to $1.50 if participants provided a cannabinoid-positive specimen or failed to submit a scheduled specimen. Values then could re-escalate according to the same schedule.
Treatment with first-generation antipsychotics does not appear to decrease substance use. Several studies suggest that clozapine decreases the use of nicotine, alcohol, or other substances among patients with schizophrenia,24 though this does not necessarily apply to other second-generation antipsychotics (Box 6).
Treating patients with comorbid schizophrenia and cannabis use
- Ask about marijuana use when evaluating all patients, particularly young ones
- Educate patients and, if appropriate, families about the risks of marijuana use. One way to do this without sounding judgmental or confrontational is to follow the principles of motivational interviewing
- Treat both the psychosis and the substance use
- Generic interventions that target drug use might be more effective than those specific to cannabis use because psychotic patients often abuse a variety of substances
- Psychoeducation might be as effective as cannabis-specific treatments
- Abstinence-based vouchers are a simple intervention with some evidence of effectiveness
- Clozapine, which seems to reduce relapse of substance use in these patients, might be the antipsychotic of choice
Implications for prevention
Psychiatric practitioners can play an important role in making young people aware of the mental health risks of using marijuana. Marijuana use fluctuates population-wide, depending in part on public perception of its harmfulness. Its use may diminish, therefore, as information on its mental health hazards percolates into high schools and the community at large. We also have the duty to make policy makers and legislators aware of this information.25
Related resources
- National Institute on Drug Abuse. https://www.drugabuse.gov/drugs-abuse/marijuana.
- Cannabis dependence. www.mentalhealth.com/dis/p20-sb03.html.
- Castle D, Murray R, eds. Marijuana and madness: psychiatry and neurobiology. Cambridge, UK: Cambridge University Press; 2004.
- Hall W, Pacula RL. Cannabis use and dependence: public health and public policy. Cambridge, UK: Cambridge University Press; 2003.
Drug brand names
- Clozapine • Clozaril
Disclosure
Dr. Rey reports no financial relationship with any company whose products are mentioned in this article or with manufacturers of competing products.