Drug interactions
Ethinylestradiol + Phenytoin
Severity: Major
Ethinylestradiol and Phenytoin: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin lowers estrogen exposure and may cause contraceptive failure, breakthrough bleeding and unintended pregnancy. This is particularly important given phenytoin's teratogenic potential.
What this interaction means in plain words
Ethinylestradiol and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Phenytoin induces CYP3A4 and hepatic conjugation, increasing ethinylestradiol clearance.
What to do
Advise a non-hormonal method such as a copper IUD or levonorgestrel IUD in place of combined hormonal contraception. Condoms may be added as backup.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Ethinylestradiol and Phenytoin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
References
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Ethinylestradiol with Phenytoin?
MediHelp rates the interaction as major. Ethinylestradiol and Phenytoin can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Phenytoin lowers estrogen exposure and may cause contraceptive failure, breakthrough bleeding and unintended pregnancy. This is particularly important given phenytoin's teratogenic potential.
How serious is the interaction between Ethinylestradiol and Phenytoin?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Advise a non-hormonal method such as a copper IUD or levonorgestrel IUD in place of combined hormonal contraception. Condoms may be added as backup.
What other medicines interact with Phenytoin?
MediHelp also lists interactions of Phenytoin with, for example, Artemether / lumefantrine, Bictegravir, Cabotegravir. The full list is on the Phenytoin page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
