Nexplanon is over 99% effective at preventing pregnancy, making it one of the most reliable reversible contraceptives available. Fewer than 1 in 100 women using the implant will experience an unintended pregnancy in the first year. Unlike the pill, patch, or ring, its effectiveness in typical everyday use is identical to its perfect-use rate, because once the small rod is placed in your upper arm, there’s nothing you need to remember or do.
How Nexplanon Prevents Pregnancy
The implant is a thin, flexible rod about the size of a matchstick that sits just under the skin of your upper arm. It steadily releases a low dose of a synthetic hormone (a type of progestin) that works in three ways: it stops your ovaries from releasing an egg each month, it thickens the mucus at the opening of your cervix so sperm have a harder time getting through, and it thins the lining of your uterus, making implantation less likely even if fertilization were to occur.
Because the hormone is delivered continuously from the rod itself, there’s no daily routine, no refills, and no room for the kind of user error that makes other methods less reliable in real life.
How It Compares to Other Methods
The implant and IUDs occupy the top tier of reversible contraception, both with typical-use failure rates below 1%. Everything else falls off sharply once you factor in real-world use. The birth control shot has a typical-use failure rate of about 4%, largely because people sometimes miss or delay their injection appointments. The pill, ring, and patch each carry a typical-use failure rate of roughly 7%, mostly due to missed doses, late replacements, or incorrect use.
The key distinction is that both the implant and IUDs are “set and forget” methods. Their perfect-use and typical-use numbers are virtually the same because they don’t require you to do anything after placement. With user-dependent methods, perfect use in a clinical sense is hard to maintain over months and years, which is why their real-world numbers are so much higher.
Does Body Weight Affect Effectiveness?
This is a common concern, and the evidence is reassuring. A systematic review published in BMJ Sexual & Reproductive Health found that the implant’s effectiveness in women with overweight and obesity falls within the same range seen across all weight groups, with failure rates between 0.0 and 1.4 per 100 woman-years. Blood levels of the implant’s hormone showed no meaningful difference across BMI categories at either three or five years of use.
In cases where pregnancies did occur in implant users with higher BMI, researchers found that other factors were more likely responsible. The most common culprits were medications that interfere with the implant’s hormone levels or uncertainty about whether the rod was properly in place at the time of conception.
How Long the Protection Lasts
Nexplanon is currently FDA-approved for three years. However, growing evidence supports its effectiveness well beyond that window. A U.S. study followed 291 implant users past the three-year mark, with 102 women continuing use for at least two additional years. No pregnancies occurred in years four and five, and hormone levels remained consistent regardless of body weight.
Based on this and similar data, the Society of Family Planning issued a clinical recommendation stating that the implant’s contraceptive effectiveness is maintained from three to five years. Merck, the manufacturer, is running a large clinical trial to potentially extend the official FDA-approved duration to five years. For now, though, the standard guidance is replacement at three years unless your provider discusses extended use with you.
When Protection Begins
Timing matters during the initial placement. If the implant is inserted within the first five days of your menstrual period, it’s effective immediately. If it’s placed at any other point in your cycle, you’ll need to use a backup method like condoms for seven days while the hormone reaches levels high enough to reliably prevent ovulation.
Medications That Can Reduce Effectiveness
Certain drugs speed up the way your liver processes the implant’s hormone, which can lower its concentration in your blood enough to compromise protection. The most notable categories include some seizure medications (such as carbamazepine, phenytoin, and topiramate), the antibiotic rifampicin (used for tuberculosis), and the herbal supplement St. John’s wort. Several HIV and hepatitis C medications can also raise or lower hormone levels unpredictably.
If you take any of these, the implant may not be the best choice for you, or you may need an additional method as backup. This is one of the few real-world scenarios where the implant’s effectiveness can drop below that 99% threshold.
Fertility After Removal
Unlike some other hormonal methods, the implant has no lingering effect on fertility. Once the rod is removed, hormone levels drop quickly, and ovulation can return within days. Some women are capable of becoming pregnant as early as one week after removal. The procedure itself is brief, typically taking just a few minutes under local anesthetic, and difficulty with removal after even five years of use is rare, occurring in about 2% of cases.