Effects of extended cannabis abstinence on clinical symptoms in cannabis dependent schizophrenia patients versus non-psychiatric controls.

BACKGROUND

Rates of cannabis use among patients with schizophrenia are high, however little is understood about clinical effects of continued cannabis use and cessation after illness onset. Therefore, we investigated the effects of 28-days of cannabis abstinence on psychotic and depressive symptomatology in cannabis dependent patients with schizophrenia.

METHOD

Males with cannabis dependence and co-morbid schizophrenia (n=19) and non-psychiatric controls (n=20) underwent 28-days of monitored cannabis abstinence. Clinical symptoms were assessed at baseline and then weekly. Abstinence was encouraged using weekly therapy sessions and contingency reinforcement, confirmed by twice-weekly urine assays.

RESULTS

Forty-two percent (8/19) of patients and 55% (11/20) of controls achieved 28-days of sustained cannabis abstinence. In patients, PANSS subscores did not change over time irrespective of abstinence status. In contrast, patient abstainers demonstrated a more pronounced reduction in depression scores compared to non-abstainers, however, the Abstinence Status x Time interaction was non-significant.

DISCUSSION

Short-term (28-days) cannabis abstinence is not associated with improvement in psychotic symptoms, but may be associated with improvement in depressive symptomatology in patients with schizophrenia. Future studies employing larger samples as well as a continuous cannabis-using group may help to better characterize the causal effects of cannabis on symptom outcomes in this disorder.