Effect of cannabis on weight and metabolism in first-episode non-affective psychosis: Results from a three-year longitudinal study

Background: Cannabis smoking is highly prevalent among patients with psychotic disorders. Its use has been found to be related to clinical characteristics and the prognosis of the disorder. Recent evidence indicates a protective effect of cannabis on weight gain and related metabolic alterations. However, there are no previous studies on the long-term longitudinal effects of cannabis on first-episode drug-naive patients, which would thereby avoid the confounding effects of chronicity and previous treatment exposure. We aimed to explore the effect of cannabis smoking on weight and lipid/glycaemic metabolic measures in a sample of first-episode non-affective psychosis patients. Method: Anthropometric measurements and glycaemic and lipid parameters were obtained at baseline and three years after initiation of treatment. Patients self-reported their cannabis use at both time points. To explore the longitudinal effect of cannabis, patients were divided into three groups: continuers, discontinuers and non-users. Results: Cannabis users at baseline presented a lower weight (F=14.85, p<0.001), body mass index (F=13.14, p<0.001), total cholesterol (F=4.85, p=0.028) and low-density lipoprotein-cholesterol (F=6.26, p=0.013) compared to non-users. These differences were also observed after three years: weight (F=8.07, p=0.005), body mass index (F=4.66, p=0.032) and low-density lipoprotein-cholesterol (F=3.91, p=0.049). Moreover, those patients discontinuing cannabis use presented a higher increase in weight (F=2.98, p=0.052), body mass index (F=2.73, p=0.067) and triglyceride-high-density lipoprotein ratio (F=2.72, p=0.067) than the non-users' and continuers'. Conclusions: The study suggests that cannabis use may produce a protective effect against weight gain and related metabolic alterations in psychosis. However, these results need to be replicated in a larger sample size.