5-alpha-reductase inhibitor (type II)
Finasteride and smoking: how tobacco affects the medication
Tobacco smoking is one of the most underappreciated drug-drug interactions in chronic medication. Compounds in tobacco smoke induce hepatic enzymes (especially CYP1A2) and can shift the plasma concentration of many medications, including Finasteride (Finasteride), enough to matter clinically at 1mg.
How smoking affects Finasteride
Polycyclic aromatic hydrocarbons in tobacco smoke induce CYP1A2 and to a lesser extent other CYP enzymes. For medications metabolised primarily by CYP1A2, smokers can have plasma levels 30–50% lower than non-smokers at the same dose. Whether Finasteride is affected depends on its specific metabolic pathway. Finasteride binds with high affinity to 5-alpha-reductase type II, blocking the conversion of testosterone into DHT.
Practical guidance
According to the prescribing information for Finasteride, smoking status should be disclosed at every dose review of Finasteride. Stopping smoking can paradoxically raise plasma levels of CYP1A2-metabolised medications enough to cause new-onset side effects within days, and may require a temporary dose reduction. The 1mg starting strength assumed in the prescribing information is usually for non-smokers.
Frequently asked questions
Does smoking change how Finasteride works? ▾
For medications metabolised by CYP1A2, yes — smokers may need higher doses or have reduced effect at standard 1mg. Whether Finasteride specifically is affected depends on whether Finasteride uses CYP1A2. The prescribing information notes any documented interaction.
Will I need to adjust Finasteride if I quit smoking? ▾
Possibly, if Finasteride is one of the medications affected by CYP1A2 induction. Stopping smoking restores CYP1A2 to normal within days, raising plasma levels and potentially causing side effects. Discuss the timing of any dose adjustment with the prescriber when planning to quit.
Products containing Finasteride
More on Finasteride
- With alcoholFinasteride and alcohol — is it safe to drink?
- With foodShould Finasteride be taken with food?
- Side effectsFinasteride side effects: common, rare and warning signs
- Dosage guideFinasteride dosage guide: how much to take and when
- OnsetHow fast does Finasteride start working?
- DurationHow long does Finasteride last?
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