Letters to the Editor
The Effect of Quetiapine on Cannabis Use in 8 Psychosis Patients With Drug Dependency
Dear Editor:
Approximately one-half of all patients with schizophrenia abuse or depend on psychoactive substances at some point during their lives (1), but few studies to date have proposed an integrated pharmacologic treatment for this schizophrenia–addiction comorbidity. Because of their strong dopamine D2 receptor antagonism, conventional antipsychotics such as haloperidol should in theory be the treatment of choice for comorbid schizophrenia and substance abuse. In practice, however, such treatment has not been demonstrated to be consistently effective and has only controlled drug abuse in special cases (2). A few pilot studies suggest that, among the conventional antipsychotics, flupenthixol may reduce cravings in schizophrenia patients with cocaine addiction (3). To date, the most promising results have been obtained with clozapine, a prototype of the atypical antipsychotics (4). Sharing certain key properties with clozapine (for example, 5-HT2– D2 ratio) (5), quetiapine may also reduce drug cravings in psychosis patients with addictions. A pilot study of 12 patients suffering from bipolar disorder (BD) and cocaine addiction appears to support this hypothesis (6). To expand on this promising result, we report case histories for 8 psychosis patients whose cannabis use habits significantly improved after treatment with quetiapine.
Case Report
The group of patients (5 men and 3 women) included 4 patients with schizophrenia and 4 with affective BD. All patients had cannabis dependency, and 2 also had a cocaine use disorder, according to DSM-IV criteria. Their mean age was 38.5 years (range 25 to 46 years). Before quetiapine was initiated, they received antipsychotics (5 patients), anti-depressants (2 patients), lithium (2 patients), clonazepam (2 patients), and procyclidine (1 patient). All 8 patients were given quetiapine for an average of 5.8 months, at dosages ranging between 100 and 1200 mg daily. Concomitantly, 4 patients received antidepressants, 2 received gabapentin, and 1 was on methadone maintenance treatment. Overall, an average 97.3% reduction in their weekly cannabis use was observed with an average quetiapine dosage of 388 mg daily. When interviewed, patients reported consuming an average of 35.6 g weekly of cannabis (range 18 to 56 g) before quetiapine introduction. After quetia- pine treatment, patients reported an average cannabis consumption of 1.1 g weekly.
Like clozapine, quetiapine has proven benefits when compared with conventional antipsychotics (7,8). First, clozapine and quetiapine have a beneficial effect on mood. Showing mesolimbic selectivity, these agents do not appear to cause extrapyramidal symptoms. Further, these medications produce little or no neuroleptic-induced dysphoria. Last, it is possible that these atypical antipsychotics (mainly clozapine) alleviate the negative and cognitive symptoms of schizophrenia more than do conventional antipsychotics. To the extent that some patients with schizophrenia may take substances as a form of self- medication, the clinical data presented here suggest that quetiapine, like clozapine, could form the basis of an integrated pharmacologic treatment for the psychosis–addiction comorbidity. Further controlled research is needed to validate the preliminary data collected to date.
Acknowledgement
The authors would like to pay tribute to Jean-Yves Roy, a pioneer psychiatrist in dual diagnosis in Montreal, who passed away in April 2004.
Funding and Support
We received no financial support, either from pharmaceutical companies or from public research institutions, to gather the data described in this letter.
Note
This report was previously presented at the annual meeting of the International Society of Addiction Medicine; October 2002; Reykjavic (Iceland).
References
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5. Gefvert O, Lundberg T, Wieselgren I-M, Bergstrom M, Langstrom B, Wiesel F-A, and others. D2 and 5HT2a receptor occupancy of different doses of quetiapine in schizophrenia: a PET study. Eur Neuropsychopharmacol 2001;11:105–10.
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8. Kasper S, Müller-Spahn F. Review of quetiapine and its clinical applications in schizophrenia. Exp Op Pharmacother 2000;1:783–801.
Stéphane Potvin, MA, Doctoral Candidate
Emmanuel Stip, MD, MSc, CFPQ
Jean-Yves Roy, MD, FRCP, CSAM
Montreal, Quebec
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