Implant Birth Control: How the Contraceptive Implant Works, Effectiveness, and Side Effects

You're weighing your birth control options, and the implant keeps coming up: a tiny rod in your arm that you can forget about for years. It sounds almost too easy. You probably have questions, though. Does it really work? Will it mess with your period? Could it break out your skin? These are fair things to ask, and the answers are reassuring once you know what to expect.

Here's the short version: the contraceptive implant is one of the most effective forms of birth control available, it goes in during a quick in-office visit, and most people tolerate it well. Let's walk through how it works, how long it lasts, the side effects to watch for, and when to check in with a clinician.

What is the birth control implant?

The birth control implant is a single, thin rod placed just under the skin of your upper arm. It contains 68 mg of a progestin hormone called etonogestrel, which it releases slowly over time. Because it's a long-acting reversible contraceptive, or LARC, you don't have to do anything day to day once it's in. That's a big part of why it's so reliable.

A clinician inserts the implant during a short office visit using a local anesthetic to numb the area. It sits under the skin, where you usually can't see it but can often feel it if you press gently. When you want it out, or when it's time to replace it, a clinician removes it through a small procedure.

How does the implant prevent pregnancy?

The implant works in three ways, according to the Mayo Clinic. First, it stops ovulation, so an egg never fully develops or gets released. Second, it thickens the mucus at the cervix, which makes it harder for sperm to get through. Third, it changes the lining of the uterus.

Together, these effects create multiple barriers to pregnancy. Because the implant keeps working around the clock without any effort from you, there's no missed pill or late refill to lower its protection.

How effective is the contraceptive implant?

The implant is one of the most effective birth control methods there is. According to the American College of Obstetricians and Gynecologists, LARC methods like the implant prevent pregnancy more than 99% of the time, with a failure rate of less than 1% in the first year of use. That means fewer than 1 in 100 users will become pregnant in that first year.

Effectiveness this high comes largely from removing human error. ACOG notes that over time, LARC methods are about 20 times more effective than the pill, the patch, or the ring, because those methods depend on using them perfectly every time. A large systematic review of the etonogestrel implant backs this up: across studies, its Pearl Index (a measure of pregnancies per 100 users per year) ranged from 0 to 1.4, and 8 of 15 effectiveness studies reported 100% effectiveness.

How long does the implant last?

The implant lasts for several years on a single insertion. The FDA recently extended the approved duration of NEXPLANON from 3 years to up to 5 years. In the clinical trial covering years 4 and 5, no pregnancies were reported and no new safety concerns came up.

That means one implant can provide continuous pregnancy protection for up to half a decade before it needs to be replaced. You can also have it removed earlier at any point if you decide you want to try to get pregnant or simply want to switch methods. Fertility is expected to return after removal.

• Approved for up to 5 years of use on a single rod
• No pregnancies reported during the years 4-5 extended-use trial
• Can be removed early at any time if your plans or needs change

What are the side effects of the implant?

The most common side effect is a change in your normal menstrual bleeding pattern. Your periods might become irregular, lighter, heavier, more frequent, less frequent, or stop altogether. This is the main reason some people choose to stop using it. According to NEXPLANON product information, about 1 in 10 women discontinue the implant because of an unfavorable change in bleeding.

Other reported side effects include headache, weight gain, acne, breast pain, vaginitis, and abdominal pain. Acne can be frustrating, especially if your skin was already prone to breakouts, since hormonal shifts are a known acne trigger. Serious risks are rare but can include blood clots and ovarian cysts, and the insertion or removal itself can cause pain, bruising, infection, or, uncommonly, injury to a nearby nerve or blood vessel.

• Most common: changes in menstrual bleeding (irregular, lighter, heavier, or absent periods)
• Other common effects: headache, weight gain, acne, breast pain, abdominal pain
• Rare but serious: blood clots, ovarian cysts, insertion/removal complications

When to see a doctor

Talk with a clinician before getting the implant so they can review your health history and confirm it's a good fit. After insertion, it's normal to have some bruising or tenderness at the site for a few days. Reach out to your clinician if you develop signs of infection at the insertion site, such as increasing redness, swelling, warmth, or drainage, or if you can no longer feel the implant under your skin.

Seek urgent or emergency care for warning signs that could point to a serious problem, including a sudden severe headache, chest pain, trouble breathing, or pain and swelling in one leg, which can be signs of a blood clot. And if bleeding changes, mood shifts, or breakouts are bothering you, it's worth a conversation rather than just toughing it out. There are often ways to manage side effects or choose a method that fits you better.