National Drug Strategy
National Drug Strategy

Comorbidity of mental disorders and substance use: a brief guide for the primary care clinician

4.1.3 Interactions between tobacco and therapeutic agents used for mental disorders

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The hydrocarbons in cigarette smoke (not the nicotine) have been shown to increase the body's ability to metabolise some medications via the cytochrome P450 system, resulting in reduced plasma concentrations of these medicationsxxx(109). As a result, people who stop smoking may find that plasma levels of certain medications increase significantly.

Nicotine can significantly decrease plasma concentrations of antipsychotics, resulting in increased dosing requirements of these medications in known smokers(2).

The metabolism of the following medications is known to be affected by cigarette smoke: clozapine(110, 111), fluphenazine, haloperidol and olanzapinexxx(112, 113). Clinically, it is recommended that the plasma levels of these medications and the presence of side effects should be monitored before and after smoking cessation(114, 115).

Antipsychotics are known to lower seizure threshold and bupropion has been known to induce seizures and psychosis. Individuals receiving these two combinations of substances are therefore more vulnerable to seizures and should be monitored closelyx(2).

Please refer to P450 website to observe possible interactions between smoking and therapeutic agents:

http://medicine.iupui.edu/flockhart/table.htm

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