A contraceptive implant is a small, flexible plastic rod placed just under the skin of your upper arm that releases a low, steady dose of a synthetic hormone to prevent pregnancy. It’s about 4 cm long (roughly the size of a matchstick) and 2 mm wide. The version available in the United States, Nexplanon, is one of the most effective forms of birth control in existence, with a failure rate of just 0.04 pregnancies per 100 women per year.
How It Prevents Pregnancy
The implant contains 68 mg of a synthetic progestin that slowly releases into your bloodstream over years. It works through three overlapping mechanisms. First, it suppresses ovulation, meaning your ovaries don’t release an egg most months. Second, it thickens cervical mucus, creating a barrier that makes it harder for sperm to reach an egg. Third, it thins the lining of the uterus, which reduces the likelihood of implantation even if fertilization were to occur.
Because the hormone is released continuously and doesn’t depend on you remembering to take a pill or replace a patch, there’s virtually no gap between “perfect use” and “typical use” effectiveness. In a large prospective study (the NORA study), only three pregnancies occurred during active implant use, producing a Pearl Index of 0.02. For context, that makes the implant roughly 50 times more effective than the pill as most people actually use it.
What the Procedure Is Like
Insertion takes just a few minutes and happens in a clinic or doctor’s office. Your provider numbs a small area on the inner side of your upper arm with a local anesthetic, then uses a preloaded applicator to slide the rod into the tissue just beneath the skin. The needle enters at a shallow angle, and you may feel some pressure, but the numbing keeps it painless. Afterward, both you and your provider will feel for the rod under your skin to confirm it’s in place, and you’ll get a small bandage and a pressure wrap to minimize bruising.
The implant contains a small amount of barium sulfate, which makes it visible on X-ray. This is a safety feature: if there’s ever a question about whether the rod has shifted, imaging can locate it precisely.
If the implant is placed within the first five days of your period, it starts working immediately. If it’s placed at any other point in your cycle, you’ll need to use backup contraception (like condoms) for seven days.
How Long It Lasts
Nexplanon was originally approved for three years of use. However, the FDA has reviewed clinical data supporting extension to five years without replacement. This means you may be able to keep a single implant in place for up to five years while maintaining highly effective contraception, though your provider can confirm what’s currently recommended based on when your implant was placed.
When the implant reaches the end of its approved duration, a new one can be inserted during the same visit the old one is removed, so there’s no gap in protection.
Changes to Your Period
Altered bleeding patterns are the most common side effect, and they’re the main reason some people choose to have the implant removed early. There’s no single “typical” experience. Some women stop getting periods altogether, some have lighter and less frequent bleeding, and others experience longer stretches of spotting, especially in the first several months.
In studies tracking bleeding diaries, about 11 to 13% of implant users had no bleeding at all in a given 90-day window. That rate stayed fairly stable over time rather than increasing. Meanwhile, the average total number of bleeding or spotting days was similar to what women experience during a natural menstrual cycle, though the pattern is often less predictable. Instead of a regular monthly period, you might have sporadic light bleeding for a few days, then nothing for weeks.
For most users, bleeding patterns settle into something more consistent after the first six to twelve months. If prolonged or bothersome bleeding continues beyond that, your provider can discuss options.
Effectiveness and Body Weight
Research has found that women with a BMI of 30 or higher have lower blood levels of the implant’s hormone compared to normal-weight women, with concentrations 31 to 63% lower in the first six months. That sounds dramatic, but researchers have been careful to note that lower hormone levels don’t automatically translate to lower effectiveness. The implant releases far more hormone than is needed to suppress ovulation, so even reduced levels remain well above the threshold required for contraception. No large study has demonstrated a clinically meaningful increase in pregnancy rates among heavier users.
Removal and Fertility Return
Removal is also a quick office procedure done under local anesthesia. Your provider makes a tiny incision near the tip of the rod and eases it out. The whole process typically takes a few minutes, though it can take longer if the implant has settled deeper into the tissue.
Fertility returns almost immediately. It’s possible to get pregnant within days of removal, because the hormone clears your system quickly once the rod is gone. If you’re having the implant removed and don’t want to become pregnant, you’ll need another form of contraception right away.
Who It Works Well For
The implant is a strong option if you want highly effective, long-acting contraception that requires zero daily maintenance. It’s suitable for people who can’t use estrogen-containing birth control (like combined pills or the patch), since it only contains a progestin. It’s also reversible on your timeline: you can have it removed whenever you choose, whether that’s six months in or at the five-year mark.
The main trade-off is unpredictable bleeding, which is a dealbreaker for some people and a non-issue for others. Unlike an IUD, the implant sits in your arm rather than your uterus, which some people prefer. And unlike injections, its effects don’t linger for months after you stop using it.