Several medications and one popular herbal supplement can reduce Nexplanon’s effectiveness enough to risk an unintended pregnancy. Nexplanon works by slowly releasing a progestin hormone called etonogestrel into your bloodstream, and certain drugs speed up how fast your liver breaks down that hormone. When blood levels of etonogestrel drop too low, ovulation can resume and the implant may fail.
How Medications Interfere With Nexplanon
Nexplanon’s hormone is processed in the liver by a specific enzyme pathway. Some drugs rev up that pathway, causing your body to clear etonogestrel faster than the implant can release it. The result is lower hormone levels in your blood, sometimes dramatically lower. In studies of one such drug, the HIV medication efavirenz, etonogestrel concentrations dropped by 49% compared to women not taking the medication. Some of these drugs also increase production of a protein that binds to circulating hormones, further reducing the amount of active progestin available to prevent pregnancy.
Specific Drugs That Reduce Effectiveness
The FDA lists the following as medications and products that can decrease Nexplanon’s effectiveness:
- Seizure medications: carbamazepine, phenytoin, oxcarbazepine, topiramate, felbamate, and barbiturates (like phenobarbital)
- Tuberculosis antibiotics: rifampin (and likely rifabutin and rifapentine, which act on the same enzyme pathway to a lesser degree)
- HIV medications: efavirenz is the most well-documented offender
- Other prescription drugs: bosentan (used for pulmonary hypertension) and griseofulvin (an antifungal)
- Herbal supplements: St. John’s wort
Among seizure medications, the risk is serious enough that clinical guidance recommends against using progestin implants at all if you take these drugs long-term. Failure rates with enzyme-inducing seizure medications are high enough that the implant is simply not considered a reliable option for those patients.
The Efavirenz Problem
The interaction between Nexplanon and certain HIV treatments deserves special attention because the data is striking. In a study of 570 HIV-positive women using a progestin implant, 12.4% of those on efavirenz became pregnant, while zero pregnancies occurred among women taking nevirapine or lopinavir-based regimens. Even doubling the implant’s hormone dose did not fully overcome the interaction with efavirenz. If you’re on HIV treatment, the specific drug you take matters enormously for implant reliability.
St. John’s Wort Is a Real Risk
St. John’s wort is an over-the-counter herbal supplement widely used for mood support, and many people don’t think of it as something that could interfere with a prescription device. But it activates the same liver enzymes as the prescription drugs listed above. The FDA considers it significant enough that women had to stop taking St. John’s wort at least two months before enrolling in Nexplanon’s clinical trials. If you use Nexplanon and take St. John’s wort regularly, you should use a backup method of contraception.
Common Antibiotics Are Not the Problem
One of the most persistent worries about hormonal birth control is that regular antibiotics cancel it out. For Nexplanon, the antibiotics most people are prescribed (amoxicillin, azithromycin, doxycycline, and similar drugs) do not interfere with the implant. The antibiotic interaction that matters is with rifampin and related tuberculosis drugs, which are rarely prescribed for everyday infections. Rifampin is a potent enzyme inducer that reduces hormone levels through the same mechanism as seizure medications. Another related antibiotic, rifaximin (sometimes used for traveler’s diarrhea), does not affect hormone levels because it isn’t absorbed into the bloodstream.
Body Weight Does Not Cancel Out Nexplanon
There’s a common concern that Nexplanon becomes less effective at higher body weights. Clinical data does not support this. In the FDA’s review of extended-use studies, 38% of participants were overweight or obese, contributing over 2,500 menstrual cycles of data. Zero pregnancies occurred across the entire study population regardless of BMI, age, or ethnicity. The implant maintained a pregnancy rate of 0.0 per 100 woman-years through five years of use, with consistent results across weight categories.
How Long Nexplanon Actually Lasts
Nexplanon is now FDA-approved for up to five years, extended from its original three-year approval. In the clinical trial supporting that extension, 399 women continued using the implant through years four and five, with no pregnancies reported across nearly 7,800 menstrual cycles. The implant must be removed by the end of the fifth year. Leaving it in past that point could mean hormone levels have dropped below what’s needed to reliably prevent pregnancy.
What to Do If You Take an Interacting Drug
If you’re prescribed any of the medications listed above, or if you’ve been regularly taking St. John’s wort, your options depend on how long you’ll need the interacting drug. For short courses (a few weeks of rifampin for a non-TB infection, for example), using condoms or another barrier method for the duration of treatment and for some time afterward is a reasonable approach. For long-term use of enzyme-inducing medications, like daily seizure drugs or certain HIV treatments, the implant is generally not recommended as your primary contraception. A copper IUD or hormonal IUD (which releases its hormone directly into the uterus rather than relying on blood levels) are typically better options in those situations.
The key distinction is between drugs that briefly overlap with your implant use and drugs you take every day. A brief interaction can be managed with backup contraception. A permanent interaction means the implant is the wrong method for you.