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The Impact of Cannabis Use on the Dosage of Antipsychotic Drugs in Patients Admitted on the Psychiatric Ward at the University Hospital of the West Indies



Objective: To assess the impact of cannabis use on the efficacy of antipsychotic drugs in male subjects presenting to the University Hospital of the West Indies (UHWI) with psychotic episodes.

Methods: Male subjects, 18–40 years old, admitted to the psychiatric ward of the UHWI between February 2013 and May 2013, diagnosed with schizophrenia, schizophreniform disorder and who tested positive for ∆9-tetrahydrocannabinol were recruited for the study.  On day one, consenting subjects were assessed using the Brief Psychiatric Rating Scale (BPRS). Patients were prescribed seven days of an oral antipsychotic medication (haloperidol, chlorpromazine, risperidone, quetiapine, olanzapine). Medicated subjects were then reassessed using the BPRS on days three and seven. Statistical analysis involved the use of Student’s t-test and repeated measure analysis of variance.

Results: In total, 20 subjects were recruited (mean age = 26.00 ± 5.96 years). Subjects were grouped based on the daily chlorpromazine equivalent (CPZE) dose given on day one into CPZE1 (CPZE dose of 100–300mg; n = 8) and CPZE2 (CPZE dose of 400–1250 mg; n = 12).  There was no significant difference in the total BPRS score between the groups on day one (CPZE1 = 41.38 ± 16.47 versus CPZE2 = 49.42 ± 25.58; p = 0.44); similar findings were obtained for the positive (26.75 ± 9.27 versus 31.83 ± 17.30; p = 0.46) and negative (14.63 ± 7.73 versus 17.58 ± 9.74; p = 0.48) symptom component on the BPRS. For subjects in CPZE1, there was no significant decrease in total BPRS score [F(2,21) = 0.07, p = 0.93] over the study period. For CPZE2, significant reduction in total BPRS scores was achieved [F(2,33) =7.12, p = 0.01], contributed by significant decrease in the positive [F(2,33) = 5.64, p = 0.02) and negative [F(2,33) = 7.53, p = 0.01) symptom components of the BPRS.

Conclusion: The findings of this study purport that male cannabis users presenting with psychotic disorders may not achieve optimal therapeutic benefit within seven days with CPZE doses ≤ 300 mg. As such, it appears that initiating treatment with CPZE doses of > 300 mg will provide better therapeutic outcomes for this patient population. 

October 27, 2014
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