The chances of getting pregnant on Nexplanon are extremely low. Fewer than 1 in 1,000 women using the implant will become pregnant in a given year, making it one of the most effective forms of birth control available. In a large observational study (the NORA study), the pregnancy rate during use was just 0.02 per 100 women-years, and under perfect conditions the failure rate has been measured at zero in multiple trials.
How Effective Nexplanon Actually Is
Nexplanon works by releasing a steady, low dose of a progestin hormone that prevents ovulation. Because it’s embedded in your arm and doesn’t depend on you remembering to take a pill or replace a patch, there’s essentially no gap between “perfect use” and “typical use.” That distinction matters a lot for methods like the pill, where real-world effectiveness drops significantly. With the implant, the two numbers are nearly identical.
The NORA study, which followed thousands of implant users, recorded only three pregnancies that occurred while the implant was actually in place. That translated to a Pearl Index of 0.02, meaning roughly 2 pregnancies per 10,000 women per year. For context, the combined birth control pill has a typical-use failure rate closer to 7 per 100 women per year, making the implant roughly 350 times more reliable in everyday conditions.
The Implant Now Lasts Five Years
The FDA updated its approval so that Nexplanon is now indicated for up to five years of use, up from the original three. A clinical trial tracking women in years four and five found zero pregnancies across nearly 8,000 menstrual cycles of use. That means you don’t need to rush to get the implant replaced at the three-year mark, though it must be removed no later than the end of the fifth year.
When Protection Starts After Insertion
Timing matters during the first week. If your implant is placed within the first five days of your period, it’s effective immediately. If it’s placed at any other point in your cycle, you’ll need to use condoms or avoid intercourse for seven days while the hormone reaches levels high enough to reliably suppress ovulation.
Does Body Weight Affect How Well It Works?
This is a common concern, and the answer has evolved. The original approval trial excluded women above a certain weight threshold, so the label once carried a warning about potentially reduced effectiveness in heavier women. A more recent FDA-reviewed study enrolled a significant proportion of overweight and obese participants (about 38% of the study population) and found that efficacy results were consistent across weight categories. That said, the FDA has noted that the newer study only covered two years, which may not be long enough to fully rule out any weight-related effect over the implant’s full lifespan. In practical terms, no clear increase in pregnancy risk has been demonstrated in higher-weight users so far.
Medications That Can Lower Effectiveness
The biggest real-world threat to Nexplanon’s effectiveness isn’t the implant itself but certain medications that speed up how your liver processes the hormone. These drugs can lower the amount of active hormone in your bloodstream enough to reduce protection. The most common culprits include:
- Seizure medications such as phenytoin, carbamazepine, oxcarbazepine, topiramate, and barbiturates
- The antibiotic rifampicin (used for tuberculosis) and the related drug rifabutin
- St. John’s wort, an herbal supplement sometimes used for mood support
- Certain HIV and hepatitis C medications, including several protease inhibitors and non-nucleoside reverse transcriptase inhibitors
Standard antibiotics like amoxicillin or azithromycin do not affect the implant. If you’re prescribed any of the medications above for ongoing use, a backup method or an alternative form of contraception is worth discussing with your provider.
What Happens If Pregnancy Does Occur
Because implant failure is so rare, the data on what happens in those uncommon cases is limited. In the NORA study, only three pregnancies occurred during active implant use. When pregnancy does happen with the implant in place, there’s a general clinical awareness that ectopic pregnancy (where the embryo implants outside the uterus, typically in a fallopian tube) should be considered. Any implant user who experiences sudden lower abdominal pain, unusual bleeding, or a positive pregnancy test should be evaluated promptly. That said, the absolute risk of any pregnancy, ectopic or otherwise, remains vanishingly small on this method.
Fertility After Removal
Unlike some long-acting methods that can delay the return of regular cycles, Nexplanon’s effects wear off quickly. It’s possible to get pregnant almost immediately after the implant is removed. Ovulation can resume within days to weeks, so if you’re having the implant taken out but don’t want to conceive right away, you’ll want another method ready to go on removal day.