Nexplanon is a small, flexible rod inserted just under the skin of your upper arm that releases a steady stream of a synthetic progestin hormone to prevent pregnancy. It works through three overlapping mechanisms: stopping ovulation, thickening cervical mucus, and thinning the uterine lining. With a failure rate of roughly 0.05%, it is one of the most effective contraceptives available.
The Three Ways It Prevents Pregnancy
The implant’s primary job is suppressing ovulation. The rod continuously releases a progestin called etonogestrel into your bloodstream, which signals your brain to stop triggering the hormonal surge that causes your ovaries to release an egg each month. No egg means no fertilization.
But Nexplanon doesn’t rely on that single mechanism. It also thickens the mucus lining your cervix, creating a barrier that makes it extremely difficult for sperm to reach an egg in the rare event ovulation does occur. On top of that, the hormone thins your uterine lining, which reduces the chance a fertilized egg could implant and develop. These layered defenses are a big reason the implant’s effectiveness is so high.
How the Hormone Release Changes Over Time
Nexplanon doesn’t deliver the same dose of hormone every day for three years. It starts strong and gradually tapers. In the first few weeks after insertion, the rod releases about 60 to 70 micrograms of etonogestrel per day. By the end of year one, that drops to roughly 35 to 45 micrograms. By year two, it’s down to 30 to 40 micrograms, and by year three, around 25 to 30 micrograms per day.
Even at these lower levels, the hormone concentration remains high enough to suppress ovulation reliably. This declining release profile is one reason side effects like irregular bleeding sometimes improve after the first year, as your body adjusts to the gradually decreasing hormone level.
How Effective It Actually Is
Nexplanon is over 99% effective. Across 15 clinical studies of the implant, not a single pregnancy was reported during proper use. Researchers have set the failure rate at 0.05% for both perfect and typical use, a distinction that matters because, unlike the pill or condoms, there’s no user error involved. Once the rod is in your arm, it works on its own. You can’t forget to take it, use it incorrectly, or store it wrong. That removes the gap between “perfect use” and “real-world use” that undermines many other contraceptive methods.
When Protection Starts
How quickly Nexplanon starts working depends on where you are in your cycle. If the implant is inserted during the first five days of your period (counting the first day of bleeding as day one), it is immediately effective. If it’s placed at any other time in your cycle, you’ll need to use a backup method like condoms for seven days while the hormone builds up to suppressive levels in your bloodstream.
How Long It Lasts
Nexplanon is FDA-approved for three years. At the three-year mark, you can have it removed, replaced with a new one, or switch to a different method. The procedure to remove or swap it typically takes only a few minutes and is done under local anesthesia in a clinic.
There is growing evidence that the implant remains highly effective beyond three years. A study following over 200 women who kept their implants in for up to five years reported zero pregnancies during years four and five. That research, published in Human Reproduction, found the implant’s contraceptive efficacy through the extended period rivaled that of other long-acting methods designed for five-year use. Some clinicians now consider extended use a reasonable option, though the official labeling still recommends replacement at three years.
What the Implant Looks Like and Feels Like
The rod itself is about the size of a matchstick. It sits just beneath the skin on the inner side of your non-dominant upper arm. Most people can feel it if they press on the area, which is actually intentional: being able to locate it by touch helps confirm it’s still properly positioned. The rod contains a small amount of barium sulfate, which makes it visible on X-rays and imaging scans. This is a design improvement over its predecessor, Implanon, and helps healthcare providers locate the implant if it ever becomes difficult to feel.
What Can Reduce Its Effectiveness
Certain medications speed up the rate at which your liver breaks down etonogestrel, potentially lowering hormone levels enough to compromise protection. The main culprits are drugs that activate a group of liver enzymes responsible for processing hormones. These include some medications used for epilepsy, certain antibiotics (particularly rifampin), some HIV treatments, and the herbal supplement St. John’s wort. If you take any of these regularly, the implant may not be reliable as your sole contraceptive method.
Body weight has also been a point of discussion. While early studies didn’t find a clear drop in effectiveness for people at higher body weights, hormone levels do run lower when the same daily dose is distributed through more tissue. In practice, the implant remains highly effective across a wide weight range, but this is one reason some providers discuss earlier replacement for people in higher weight categories.
Common Side Effects
The most frequently reported side effect is a change in menstrual bleeding patterns. Some people experience lighter, less frequent periods. Others have irregular spotting that can last for months, particularly in the first year. A smaller percentage stop getting periods altogether, which is not harmful but can be unsettling if unexpected. Bleeding changes are the number one reason people ask to have the implant removed early.
Other possible side effects include headaches, mood changes, acne, breast tenderness, and weight fluctuation. Because the implant uses only a progestin and contains no estrogen, it avoids some of the risks associated with combination hormonal methods, such as increased blood clot risk. This makes it a viable option for people who can’t use estrogen-containing contraceptives.
How It Differs From Other Long-Acting Methods
Nexplanon belongs to the same category as IUDs: long-acting reversible contraceptives, sometimes called LARCs. The key difference is location and hormone type. Hormonal IUDs release their progestin directly into the uterus, so most of the effect is local. Nexplanon releases its hormone into your bloodstream, creating a system-wide effect that more reliably suppresses ovulation. The copper IUD, by contrast, uses no hormones at all.
Fertility returns quickly after removal. Most people begin ovulating again within a few weeks, and the hormone clears from the body rapidly once the rod is taken out. This makes Nexplanon a fully reversible method despite its long duration of action.