Synthetic progestin (emergency contraception)
Levonorgestrel 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 Levonorgestrel (Levonorgestrel), enough to matter clinically at 1.5mg.
How smoking affects Levonorgestrel
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 Levonorgestrel is affected depends on its specific metabolic pathway. In emergency contraception, levonorgestrel works primarily by delaying or inhibiting ovulation when taken before the LH surge.
Practical guidance
According to the prescribing information for Levonorgestrel, smoking status should be disclosed at every dose review of Levonorgestrel. 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 1.5mg starting strength assumed in the prescribing information is usually for non-smokers.
Frequently asked questions
Does smoking change how Levonorgestrel works? ▾
For medications metabolised by CYP1A2, yes — smokers may need higher doses or have reduced effect at standard 1.5mg. Whether Levonorgestrel specifically is affected depends on whether Levonorgestrel uses CYP1A2. The prescribing information notes any documented interaction.
Will I need to adjust Levonorgestrel if I quit smoking? ▾
Possibly, if Levonorgestrel 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 Levonorgestrel
More on Levonorgestrel
- With alcoholLevonorgestrel and alcohol — is it safe to drink?
- With foodShould Levonorgestrel be taken with food?
- Side effectsLevonorgestrel side effects: common, rare and warning signs
- Dosage guideLevonorgestrel dosage guide: how much to take and when
- OnsetHow fast does Levonorgestrel start working?
- DurationHow long does Levonorgestrel last?
The information on this website is provided for reference and educational purposes only. It does not replace consultation with a qualified healthcare professional.