Components of tobacco smoke can induce metabolic enzymes, particularly CYP1A2, which affects medicines including clozapine and olanzapine. Smoking can therefore increase clearance and reduce exposure compared with otherwise similar circumstances. Reducing or stopping smoking can allow drug concentrations to rise, potentially increasing adverse effects.
Smoking is common among people receiving care for schizophrenia, but patterns and reasons vary. Tobacco smoke and nicotine have different pharmacological roles, which matters when discussing medication interactions. Assessment should address dependence, physical health and treatment exposure without assuming that smoking is necessary for cognitive function or that cessation support is unsuitable for people with psychosis.
The interaction is mainly caused by combustion-related compounds, not nicotine itself. Nicotine replacement does not reproduce the same enzyme-inducing effect. Changes during hospital admission or a move to a smoke-free setting are especially important to communicate. Returning to smoking can alter exposure in the opposite direction. Dose decisions require clinical review and sometimes concentration monitoring; they should not be made by applying a general percentage from an article. Understanding the distinction between smoke and nicotine helps prevent both medication toxicity and loss of effectiveness during changes in tobacco use.
A move from smoking to nicotine replacement or another non-combustible source can still change drug metabolism because smoke exposure falls. Conversely, resuming cigarettes can lower concentrations of relevant medicines. The prescribing team should know about both directions of change. Monitoring and any dose decision are drug-specific, particularly for clozapine, rather than based on nicotine intake alone.
Further reading: NICE clinical guideline; NHS Specialist Pharmacy Service.
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