ABSTRACTdiagnosed with a psychotic disorder and are receiving prescription medication for the same. A trawl of the literature indicated that information on the direct pharmacological interactions between cannabis and antipsychotic medications seem to be undocumented. One known fact, however, is that there are higher risks of exaggerated symptoms and/or relapse in patients diagnosed with psychosis who also have a history of concomitant cannabis use. However, the underlying pathophysiology is unclear (6, 7).Anecdotally, it has been reported that subjects admitted to the psychiatric ward of the University Hospital of the West Indies (UHWI) with a history of cannabis use require a higher dose of antipsychotic medication in order to achieve adequate clinical control. The aims of this study were to ascertain if the doses of antipsychotic medications prescribed by the clinicians were determined by the severity of the patients' conditions and to assess the influence of cannabis use on the efficacy of antipsychotic drug therapy.