Answer
Tobacco smoke changes the metabolism of some medicines. When smoking stops, their blood levels or effects may change even though varenicline itself has few direct interactions.
Sources for this answer
- Varenicline 0.5 mg film-coated tablets — Current selected SmPCemc · Summary of Product Characteristics
- NHSNHS · NHS medicine guidance
General medicine information. Follow the instructions for your own medicine and speak to a pharmacist or clinician about your individual circumstances.