By Liam Davenport, medwireNews Reporter
The amount of cannabis used does not appear to be associated with the severity of symptoms in patients with established psychosis, although the drug is linked to a small effect on psychosocial functioning, say UK scientists.
Seeking to explain the lack of overall effect of cannabis dose, the team, led by Christine Barrowclough (University of Manchester), says: "There may have been substantial variation in the relationship between cannabis consumption and outcome in subgroups of the cannabis users, and we would suggest that for some people with established psychosis, the continued effects of cannabis are likely to be much more closely related to the course of psychosis than for others."
The researchers compared demographic, clinical, and substance use variables of 160 patients with established nonaffective psychosis whose substance use included cannabis with those of 167 established psychosis patients who used other substances. Clinical assessments and substance use were assessed at baseline, 12 months, and 24 months.
Although cannabis users did not differ from other substance users in terms of positive psychotic symptoms, multivariate analysis revealed that they were significantly younger, less likely to use alcohol above safe limits, more likely to be of Black or Asian ethnicity, more likely to be noncompliant with antipsychotic medication, and had fewer negative symptoms than other substance users.
Of the cannabis users, 31% met the criteria for dependence or abuse, and the average consumption per day was 2.4 g. In all, 60% of cannabis users had reduced their daily use at 12 months and 67% had at 24 months.
Average daily weight of cannabis consumption was not linked to Positive and Negative Syndrome Scale subscales, rates of hospital admission and relapse, or predicted outcomes.
In adjusted analyses, change in daily cannabis consumption was significantly associated with Global Assessment of Functioning (GAF) total scores, but an increase in average daily consumption of 1 g was linked to a decrease in GAF total score of just 1.05.
"While not everyone will demonstrate durable symptomatic improvements from cutting down or abstaining from cannabis, there are significant negative impacts from cannabis use in terms of physical health and risk of other mental health problems and associated problems such as medication nonadherence may be easier to address once cannabis use has been reduced," the team concludes in Schizophrenia Bulletin.
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