In comparison, rates of other comorbid substance dependence were significantly increased in comorbid vs. non-comorbid groups at both time-points, except for sedative dependence. Further, no significant difference for any SUD was found comparing comorbid bipolar I vs. bipolar II group members. Since cannabinoids also have some sedative and hypnotic characteristics, users of cannabinoids may therefore abuse other sedatives (e.g., benzodiazepines), less often than other substances such as alcohol, stimulants, or cocaine. However, these results do not support a potential protective effect of CU and abuse from sedative dependence. Individuals with multiple SUDs also include CUD along with alcohol, opioids, stimulants, and cocaine use disorders. Further, the results do not support a ‘gateway’ hypothesis of cannabinoids i.e., CU early in life subsequently increases the risk for developing other alcohol and SUDs. To test this “gateway hypothesis”, a different study design (e.g., longitudinal studies on cannabis users during adolescence and early adulthood) is needed.
