Mortality in substance‐induced psychosis: a register‐based national cohort study

Aims We aimed to analyze whether people with substance‐induced psychosis (SIP), both those who convert and do not convert to schizophrenia, have higher all‐cause and cause‐specific mortality when compared to the general population. Design Prospective cohort study. Setting Nationwide Danish registers. Participants/Cases We included all people born in Denmark, living in Denmark on their 15th birthday, and age 15 or more during the study period from January 1, 1994, and August 10, 2017. Measurements Exposure was categorized as: (i) neither SIP nor schizophrenia; (ii) SIP without preceding schizophrenia; (iii) SIP converted to schizophrenia; and (iv) schizophrenia without preceding SIP. Any SIP and substance‐specific SIPS were examined regarding all‐cause and cause‐specific mortality. Findings The study included a total of 5 619 691 individuals. Compared to people with neither schizophrenia nor SIP, people with SIP without preceding schizophrenia had an increased risk of dying (hazard ratio [HR] = 6.23, 95% CI = 5.96–6.50), as had those with SIP converting to schizophrenia (HR = 9.77, 95% CI = 8.84–10.79) and those with only schizophrenia (HR = 3.07, 95% CI = 3.03–3.13). A similar pattern, albeit with higher HRs, was observed for suicides and accidental deaths. Other cause‐specific‐mortality groups also generally showed the same pattern, as did types of individual substances. Conclusions Substance‐induced psychosis was strongly associated with an increased risk of both all‐cause and cause‐specific mortality, even among cases who did not convert to schizophrenia. This provides a strong rationale for monitoring people with previous diagnosis of substance‐induced psychosis and developing and implementing interventions to reduce this excess mortality.