Drug interactions
Levonorgestrel + Phenytoin
Severity: Major
Levonorgestrel and Phenytoin: major interaction.
Last updated
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 can lower levonorgestrel concentrations and reduce contraceptive efficacy, raising the risk of unintended pregnancy. This applies to both regular and emergency contraception.
What this interaction means in plain words
Levonorgestrel 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.
Levonorgestrel belongs to Endocrine; Phenytoin belongs to Central Nervous System.
Why it happens
Phenytoin induces CYP3A4, increasing levonorgestrel metabolism.
What to do
Advise a non-hormonal or non-affected method such as a copper IUD or levonorgestrel IUS. For emergency contraception, consider a copper IUD or a higher levonorgestrel dose per local guidance.
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?
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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
Other interactions of Levonorgestrel
Frequently asked questions
Can I take Levonorgestrel with Phenytoin?
MediHelp rates the interaction as major. Levonorgestrel 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 can lower levonorgestrel concentrations and reduce contraceptive efficacy, raising the risk of unintended pregnancy. This applies to both regular and emergency contraception.
How serious is the interaction between Levonorgestrel 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 or non-affected method such as a copper IUD or levonorgestrel IUS. For emergency contraception, consider a copper IUD or a higher levonorgestrel dose per local guidance.
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.
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