Answer
Tobacco smoke changes the metabolism of some medicines. When smoking stops, their exposure or effect may change even though varenicline itself has few direct interactions.
Sources for this answer
- Varenicline 1mg 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.