Nexplanon is one of the most effective contraceptives available, with a failure rate of just 0.05% in the first year of use. That translates to about 1 pregnancy per 2,000 users. A large post-market study (the NORA study) tracked thousands of implant users and found a Pearl Index of 0.04, meaning fewer than 1 in 2,000 women became pregnant per year of use. By virtually any measure, it outperforms pills, patches, rings, and even most IUDs.
How It Compares to Other Methods
The gap between the implant and other contraceptives is striking, especially when you factor in real-world use. The pill has a typical-use failure rate of 9% per year, mostly because people miss doses, take them late, or stop refilling prescriptions. The implant’s typical-use and perfect-use failure rates are identical at 0.05%, because once it’s in your arm, there’s nothing to remember or mess up.
Compared to IUDs, the implant still holds a slight edge. The hormonal IUD (Mirena) has a typical-use failure rate of 0.2%, and the copper IUD (Paragard) sits at 0.8%. Both are excellent, but the implant is roughly four times more effective than the hormonal IUD and sixteen times more effective than the copper one. This makes Nexplanon the single most effective reversible contraceptive on the market.
Why the Failure Rate Is So Low
The implant works through three overlapping mechanisms. Its primary job is suppressing ovulation: if no egg is released, pregnancy can’t happen. It also thickens cervical mucus, creating a barrier that makes it harder for sperm to reach the uterus. Finally, it changes the uterine lining in ways that make implantation less likely. These effects kick in quickly. If the implant is placed within the first five days of your period, it’s effective immediately. If placed later in your cycle, you need a backup method like condoms for seven days.
Because the implant releases a steady, low dose of hormone directly into your bloodstream, it doesn’t depend on your digestive system (unlike the pill) or your ability to keep a device properly positioned (unlike the ring). There’s very little you can do to accidentally reduce its effectiveness, which is why typical use and perfect use produce the same numbers.
Does Body Weight Affect How Well It Works?
This is a common concern, and the evidence is reassuring. A systematic review of the available research found that implant effectiveness in people with overweight and obesity falls within the same range seen across all weight groups. While one pharmacokinetic study found that hormone levels in the blood were numerically lower in people with a BMI of 30 or above, this didn’t translate to more pregnancies.
Across the observational studies reviewed, no pregnancies were reported among users with a BMI between 25 and 30. Among users with a BMI of 30 or higher, only two pregnancies were reported across multiple studies, and in both cases the researchers concluded that other factors, specifically medications that speed up hormone metabolism and uncertainty about whether the implant was properly placed, were more likely explanations than weight alone. In short, there is no strong evidence that a higher BMI makes Nexplanon less effective.
Medications That Can Reduce Effectiveness
The one well-documented threat to implant effectiveness is a category of drugs called enzyme inducers. These medications rev up liver enzymes that break down hormones faster than usual, lowering the concentration of the implant’s active hormone in your blood. The most common culprits are certain anti-seizure medications, some HIV treatments, and the antibiotic rifampin (used for tuberculosis). The herbal supplement St. John’s wort has a similar effect.
If you take any of these medications regularly, the implant may not be your best option, or you may need an additional method. This is worth discussing with your prescriber, because the interaction applies to most hormonal contraceptives, not just the implant.
Effectiveness Beyond Three Years
Nexplanon is FDA-approved for three years of use, but clinical evidence suggests it remains highly effective for longer. A study that followed 204 implant users out to five years found zero pregnancies during years four and five. The overall five-year pregnancy rate was 0.6 per 100 women-years, comparable to the five-year rate for the two-rod implant system. The researchers concluded that the implant maintains the same contraceptive effectiveness beyond three years and up to five, with no major differences in side effects.
This doesn’t mean you should ignore the approved timeline on your own. Regulatory approval involves a specific evidence threshold, and your provider can help you weigh whether extended use makes sense for your situation. But the data is encouraging for anyone who hasn’t been able to schedule a timely replacement.
Fertility After Removal
One of the most important things about long-acting contraceptives is what happens when you stop. The implant does not cause lasting changes to fertility. In a study of over 600 women who had their implants removed because they wanted to become pregnant, 20% conceived within one month. By six months, 63% were pregnant. By one year, 80% had conceived, and by two years that number reached 88%. These rates are consistent with what you’d expect in the general population trying to conceive.
Age did play a role. Women who had their implants removed after age 30 took a median of six months to conceive, compared to about four months for women under 30. But this mirrors the natural age-related decline in fertility and isn’t caused by the implant itself.
When the Rare Failures Happen
The small number of pregnancies that do occur with the implant tend to cluster around specific situations. In the NORA study, six pregnancies were identified: three occurred while the implant was in place, and three occurred within seven days of removal. The most commonly cited risk factors in the broader literature are concurrent use of enzyme-inducing medications and improper insertion (meaning the device wasn’t correctly placed under the skin). If your provider confirms the implant is palpable in your arm after insertion, and you aren’t taking interacting medications, the chance of failure is extraordinarily low.