Published: 10 July 2017
In The Lancet Psychiatry, Schoeler and colleagues present a study describing the mediating effect of medication adherence on the association between continued cannabis use and relapse risk in patients with first-episode psychosis. They have previously reported a relapse rate of 36% in this patient group over a 2-year period.
Acknowledging the potential risk of psychosis relapse related to the high proportion of patients continuing cannabis use after the onset of psychosis, the current study1 investigates the same patient group consisting of 245 patients, obtaining retrospective data on active cannabis use and medication adherence shortly after illness onset, as well as risk of relapse at 2-year follow-up. The authors find that relapse of psychosis associated with continued cannabis use is partly mediated through non-adherence to prescribed antipsychotic medication.
It is well established that cannabis use increases the risk of schizophrenia, not only from the early Swedish conscript studies but also from studies on people who use sinsemilla in London, UK, showing that high potency cannabis increases the risk of schizophrenia. Twin studies from Norway have shown that cannabis increases the risk of psychosis, even when controlling for genetic factors. There has been discussion on the direction of the association, as none of these studies can rule out reverse causality, but it seems reasonable to conclude that cannabis is one of many stressors that can precipitate schizophrenia, at least in susceptible individuals.