Etonogestrel and Felbamate: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Felbamate
Etonogestrel
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced etonogestrel exposure, reduced efficacy of etonogestrel and an increased risk of breakthrough bleeding/contraceptive failure
Interaction Deep Dive
Concomitant use of a combined hormonal contraceptives (CHCs), such as etonogestrel with a CYP3A4 inducer, such as felbamate may reduce CHCs exposure and may lead to reduced efficacy of CHCs or an increase in breakthrough bleeding. Counsel women to use an alternative non-hormonal method of contraception or a back-up method when CYP3A4 inducers are used with CHCs and to continue back-up non-hormonal contraception for 28 days after discontinuing the CYP3A4 inducer to ensure contraceptive reliability1.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of etonogestrel
Common questions
Can I take Etonogestrel and Felbamate together?
Reduced etonogestrel exposure, reduced efficacy of etonogestrel and an increased risk of breakthrough bleeding/contraceptive failure Always confirm with your pharmacist or prescriber before making any change.
How serious is the Etonogestrel and Felbamate interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Etonogestrel or Felbamate need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: NuvaRing(R) vaginal ring, etonogestrel ethinyl estradiol vaginal ring. Organon & Co. (per FDA), Jersey City, NJ, 2024.
Keep reading about Felbamate
Keep reading about Etonogestrel
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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