First-episode psychosis patients who continue to use marijuana after beginning treatment are more likely to adhere to their medication regimen than are cannabis users who quit. But continued users also are more likely to have increased levels of symptoms after adjustment for this adherence, according to a small prospective 1-year study published in Schizophrenia Research.

The study found no significant differences between continued marijuana users and those who quit after beginning treatment in terms of the patients’ depression severity, time to remission, risk of relapse in the first year of treatment, or scores on the Positive and Negative Syndrome Scale (PANSS).

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Psychosis patients who smoke marijuana show a better likelihood to adhere to drug regimens.

Previous research has shown that 18%-30% of first-episode psychosis (FEP) patients regularly use marijuana and 40%-60% meet the criteria for lifetime diagnosis of cannabis abuse or dependence. Dr. Kia Faridi at the Prevention and Early Intervention Program for Psychosis (PEPP-Montreal) and his associates set out to determine whether a link exists between medication adherence and continuation of marijuana use, and whether this interaction affect symptom levels a year later (Schizophr. Res. 2012;141:78-82 [doi:10.1016/j.schres.2012.07.023])

From 192 FEP patients consecutively admitted to PEPP, the authors identified 62 who met the DSM-IV criteria at baseline for active cannabis use disorder or polysubstance disorder with cannabis. The authors were able to collect sufficient data for 48 of these patients for the full year of the study.

All 48, like the others admitted to PEPP, were aged 14-30, met the DSM-IV criteria for psychotic symptoms for at least a week, and had less than a month of past treatment with antipsychotics. The population was predominately male, and more than half came from lower-middle or lower socioeconomic class.

Once entering treatment, 20 of them (41.2%) stopped using marijuana and 28 patients (58.7%) continued. Researchers interviewed the patients every 3 months to determine medication adherence, defined as taking medications more than 75% of the time. At the 6-month follow-up, adherence dropped for both groups. However, it picked back up for the marijuana users by the 12-month follow-up, when 92% of them were regularly taking their antipsychotics, compared with adherence among only 40% of the patients no longer using marijuana (P less than .01).

This finding surprised the researchers, since it conflicts with past research. But they noted the small sample size and hypothesized that those who quit using marijuana may be attributing their psychosis symptoms to the THC and therefore neglecting to continue with medication after having ceased using marijuana. Meanwhile, those who continue to use marijuana may be deciding to stick with their medications to treat ongoing psychosis symptoms.

Cannabis use was significantly associated with higher levels of symptoms – but only after researchers controlled for medication adherence (P = .03). Secondarily, the study revealed that a good number of patients using marijuana can stop using it after entering treatment despite the link between quitting marijuana and lower medication adherence. “Unsurprisingly, patients with more severe substance use disorder at baseline were more likely to persist in using cannabis,” the authors wrote.

The authors said their findings point out the value of helping patients stop (or reduce) marijuana use because of the drug’s apparent negative influence on their psychotic symptoms.

Dr. Faridi’s fellowship is partly funded by Pfizer Canada. The other authors cited funding from Pfizer Canada, the Canada Research Chairs Program, and multiple pharmaceutical companies.