Does Emend Interact with Hormonal Birth Control?
Yes, Emend (fosaprepitant/aprepitant) reduces the effectiveness of hormonal contraceptives, including pills, patches, injections, implants, and vaginal rings. This happens because aprepitant induces CYP3A4 enzymes in the liver, speeding up the metabolism and lowering blood levels of progestins and estrogens.[1][2]
Patients using Emend for chemotherapy-induced nausea should use a non-hormonal backup method, like condoms, during treatment and for up to 28 days after the last dose.[1]
How Long Does This Interaction Last?
Aprepitant affects hormone levels for about 28 days post-dose due to its lingering enzyme induction. Fosaprepitant converts to aprepitant quickly, so the interaction starts with the first IV dose.[1][3]
What Do Guidelines Recommend?
FDA labeling and product inserts advise against relying on hormonal birth control alone. Use barrier methods or switch to non-hormonal options like copper IUDs during and after Emend use.[1][2] No dose adjustments fix this—backup contraception is required.
Are There Exceptions or Other Drugs Involved?
The interaction applies to the full 3-day Emend regimen (IV day 1, oral days 2-3). Single-day oral aprepitant has a milder effect but still warrants caution. Combined with other CYP3A4 inducers like rifampin, risks increase.[1]
Emend's oral form (aprepitant) carries the same warning. No data shows interaction with progestin-only methods being less severe—all hormonal types are impacted.[2]
What About Pregnancy Risks During Treatment?
Unintended pregnancy risk rises due to failed contraception. Emend is pregnancy category B (no clear human risk), but chemo context adds fetal harm potential from other drugs. Discuss with providers immediately if pregnancy occurs.[3]
[1]: Emend (aprepitant) Prescribing Information - Merck
[2]: FDA Drug Interactions Table - Hormonal Contraceptives
[3]: Drugs.com - Emend Drug Interactions