The association of cannabis use with quality of life and psychosocial functioning in psychosis.

Background: Cannabis use is highly prevalent among people with a psychotic disorder. They often report sociality, coping with unpleasant affect and having positive experiences as important reasons for cannabis use, suggesting that cannabis improves their quality of life (QoL) and psychosocial functioning. However, based on previous studies we hypothesize that cannabis use is negatively associated with long-term subjective QoL and psychosocial functioning in people with a psychotic disorder.

Methods: We included 2994 people with a psychotic disorder (36.4% female), mean age 44.4 (SD 11.9), mean illness duration 17.2 years (SD 11.1), who participated in two yearly routine outcome assessments between 2014 and 2018 (interval 9-15 months) from the naturalistic PHAMOUS cohort study. Linear regression analyses were used to examine whether first assessment cannabis use was associated with QoL (ManSA) and psychosocial functioning (HoNOS). Changes in outcomes between assessments were analyzed with AN(C)OVA, to examine differences between continuers (n = 255), discontinuers (n = 85), starters (n = 83) and non-users (n = 2571).

Results: At first assessment, 11.4% was using cannabis. They had lower QoL (B = -2.93, p < 0.001) and worse psychosocial functioning (B = 1.03, p = 0.002) than non-users. After one year, changes in QoL and psychosocial functioning were not significantly different between continuers, starters, discontinuers and non-users.

Conclusions: Cannabis users were less satisfied with their family relations and financial situation and showed more aggressive and disruptive behavior and self-harm than non-users. These differences are likely the result of patients having used cannabis for many years. Starting or discontinuing cannabis did not lead to changes in QoL and psychosocial functioning within one year.