Psychopathology among cannabis-dependent treatment seekers and association with later substance abuse treatment

We determined the proportion of psychiatric treatments for disorders not due to substance use among a cohort of subjects (n = 3,114) seeking treatment for cannabis dependence. Data were retrieved from Danish treatment registers. Cases were compared with a representative sample, which was randomly selected from the general population according to age and gender (n = 15,570). Cannabis users were followed, and reentry into substance abuse treatment was used as an outcome deploying Cox regression analysis. The proportion of treatment for all psychiatric disorders was much higher among cases than among controls: schizophrenia (odds ratio [OR] = 7.9; 95% confidence interval [95% CI] = 6.1–10.2), bipolar disorders (OR = 4.9; 95% CI = 2.8–8.5), other affective disorders (OR = 7.6; 95% CI = 6.1–9.5), and personality disorders (OR = 17.3; 95% CI = 14.5–20.5). All in all, 40.7% of cases, compared with 5.2% of controls, had received psychiatric treatment (OR = 12.5; 95% CI = 11.3–13.8). A history of psychiatric treatment was associated with increased rates of reentry into substance abuse treatment, in general (OR = 1.35; 95% CI = 1.20–1.53), specifically for cannabis (OR = 1.26; 95% CI = 1.07–1.48) and opioid (OR = 1.56; 95% CI = 1.23–1.99) dependence. This is the first study to show that the proportion of psychiatric treatment is much elevated among subjects seeking treatment for cannabis dependence, and that a history of psychiatric problems is associated with higher rates of reentry into substance abuse treatment.