A systematic review found that cannabis use in people with psychosis was associated with increased odds of non-remission, more antipsychotic medications prescribed, higher clozapine use, and poorer treatment trajectories.
Psychiatrists, psychosis patients, and their families.
Cannabis linked to increased non-remission and clozapine prescription
What the researchers found
Seven studies met inclusion criteria. Cannabis use was associated with increased odds of non-remission, prescription of more unique antipsychotic medications, cumulative clozapine prescription, and poor treatment trajectories. One study found lower past-year cannabis use in clozapine patients, and another found differences in chlorpromazine equivalent doses for olanzapine.
Why it matters
Treatment failure in psychosis often leads to escalation through multiple medications, eventually reaching clozapine. If cannabis is a modifiable factor contributing to this progression, early cessation could prevent unnecessary treatment intensification.
The numbers in context
7 studies included. Cannabis associated with increased non-remission, more unique antipsychotic prescriptions, more clozapine prescriptions, and worse treatment trajectories.
How the study worked
Systematic review of Ovid databases (Embase, MEDLINE, PsycINFO) for studies examining cannabis use and antipsychotic treatment failure in psychosis patients. Seven articles met eligibility.
What this study cannot tell us
Only seven studies met criteria, highlighting the paucity of research. Heterogeneous study designs and variable definitions of cannabis use and treatment failure. No prospective studies specifically designed to test this question.
How to read the evidence
Moderate: systematic review methodology, but limited to seven heterogeneous studies.
When this study was published
Published in 2019.
The bigger picture
The clinical pathway from first antipsychotic to clozapine represents increasingly difficult treatment. Cannabis use may be accelerating patients along this pathway, but the evidence base remains thin and methodologically limited.
Questions still open
- Does cannabis directly cause antipsychotic resistance, or is cannabis use a marker for more severe illness? Would cannabis cessation improve treatment response? Are there pharmacokinetic interactions between cannabis and antipsychotics?
Common questions
What is clozapine?
Why would cannabis make antipsychotics work less well?
Read the original research
Antipsychotic treatment failure in patients with psychosis and co-morbid cannabis use: A systematic review.
Psychiatry research, 280, 112523
Citation
Reid, Sam; Bhattacharyya, Sagnik. (2019). Antipsychotic treatment failure in patients with psychosis and co-morbid cannabis use: A systematic review.. Psychiatry research, 280, 112523. https://doi.org/10.1016/j.psychres.2019.112523
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