Background: The health burden of cannabis use in patients with other substance dependencies is not fully understood.
Objective: To assess the impact of cannabis use as secondary drug on mortality of patients with other major substance use disorders.
Participants: Patients with opiate, cocaine, or alcohol dependence admitted to detoxification from 2001 to 2010 at a teaching hospital in Badalona, Spain.
Main measurements: Sociodemographic characteristics, drug use, medical comorbidities, and urine drug screens were obtained at admission. Deaths were ascertained through clinical records and a death registry. Mortality rates and Cox regression models were used to analyze the association between urinary cannabis and mortality.
Results: A total of 474 patients (20% women) were admitted with a median age of 38 years (interquartile range: 32-44 years). The main substances that motivated admissions were opiates (27%), cocaine (24%), and alcohol (49%). Positive urinary cannabis was detected in 168 patients (35%). Prevalence of cannabis use among patients with opiate, cocaine, or alcohol dependence was 46.5%, 42.9%, and 25.5%, respectively. At admission, 110 (23.7%) patients had human immunodeficiency virus infection and 217 (46.5%) had hepatitis C virus infection. Patients were studied for a median of 5.6 years (interquartile range: 2.6-7.7 years) (2454.7 person-years), and at the end of the study, 50 patients (10.5%) had died, yielding a mortality rate of 2.04 × 100 patient-years (95% confidence interval: 1.53-2.66). There was no association between cannabis detection and overall mortality in the adjusted regression models [hazard ratio (95% confidence interval): 1.12 (0.60-2.00), P = 0.73], but acquired immune deficiency syndrome-related deaths were more frequent in those positive for cannabis (26% vs 2%, P = 0.03).
Conclusion: Positive urinary cannabis did not confer an increased risk of death in patients with severe opiate, cocaine or alcohol dependence.