Abstract: Background: Cannabis smoking is highly prevalent among patients with a psychotic disorder. Its use has been found related to clinical characteristics of the disorder including age of onset, symptoms severity and cognitive impairment. However, recent studies, both in healthy subjects and patients with psychosis, propose a possible protective effect of cannabis on weight gain and related metabolic alterations. Even so, there are no previous studies on the long-term longitudinal effect of cannabis on first-episode drug-naïve patients, thus not avoiding confounding effects of chronicity and previous treatment exposure. We aimed to explore the effect of cannabis smoking on weight and lipid/glycemic metabolic measures in a sample of first-episode non-affective psychosis patients. Material and methods: Anthropometric measurements and glycemic and lipid parameters were obtained at baseline and after 3 years of having initiated treatment. Patients were divided into two groups depending on self-reported cannabis use (cannabis users and non-users). Results: Cannabis users presented at baseline lower weight (F = 14.85, P < 0.001), BMI (F = 13.14, P < 0.001), total cholesterol (F = 4.85, P = 0.028) and LDL-cholesterol (F = 6.26, P = 0.013), than non-users. These differences were also observed at 3 years: weight (F = 8.07, P = 0.005), BMI (F = 4.66, P = 0.032) and LDL-cholesterol (F = 3.91, P = 0.049). Conclusions: Our results support the hypothesis that cannabis has a protective effect against weight gain and related metabolic alterations that are frequently observed in psychotic patients. However, this positive effect does not overcome the well known negative impact of cannabis on psychosis prognosis. Thus, clinicians should continue recommending cannabis use cessation, although being aware of a probable occurrence of a deterioration in metabolic parameters.

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