The birth control implant is a small, flexible rod placed just under the skin of your upper arm that releases a steady, low dose of a synthetic hormone to prevent pregnancy. It’s over 99% effective, making it one of the most reliable contraceptive methods available, and it works for up to five years before needing replacement.
How the Implant Prevents Pregnancy
The implant works through two primary mechanisms. First, it suppresses ovulation. The hormone it releases signals your brain to reduce the hormonal surge that normally triggers an egg’s release each month. Without ovulation, there’s no egg available to be fertilized. This is the implant’s main line of defense, and it’s remarkably consistent.
Second, the implant thickens your cervical mucus. This sticky, dense mucus acts as a physical barrier, preventing sperm from reaching the fallopian tubes where fertilization would normally take place. Even if ovulation were to occur in rare cases, sperm would have a very difficult time getting through.
The implant also causes changes to the uterine lining, which could theoretically make implantation less likely. However, the contributions of this third effect are hard to measure, and the first two mechanisms do most of the heavy lifting.
What Insertion Feels Like
The implant is about the size of a matchstick. A healthcare provider inserts it on the inner side of your upper arm, over the triceps muscle, using a special applicator with a pre-loaded needle. You’ll receive a local anesthetic first, so the procedure itself is mostly painless. The needle goes in at a shallow angle and slides the rod just beneath the skin surface. The whole process takes only a few minutes.
Afterward, your provider will have you feel the implant under your skin to confirm it’s in the right spot. You’ll leave with a pressure bandage to reduce bruising, which you can remove after 24 hours. A smaller adhesive bandage stays on for three to five days. Some bruising and tenderness at the site is normal for the first week or so.
Effectiveness Compared to Other Methods
The implant’s effectiveness rate is the same whether you measure “typical use” or “perfect use,” and that’s what sets it apart from most other contraceptives. With the pill, the patch, or condoms, there’s a gap between how well they work in theory and how well they work in real life, because those methods depend on you doing something correctly every time. The implant doesn’t. Once it’s in your arm, it’s working. Fewer than 1 in 100 women using the implant will experience an unintended pregnancy in the first year.
How Long It Lasts
The FDA approves the implant for up to five years of continuous use. It must be removed by the end of that fifth year. If you want to keep using this method, a new implant can be placed in the same visit as the removal. There is no approved use beyond five years, so don’t plan on stretching it further.
Changes to Your Period
Irregular bleeding is the most common side effect and the top reason people have their implant removed early. Your bleeding pattern on the implant is unpredictable, especially in the first several months. Some people stop getting periods entirely, a condition called amenorrhea. Others experience infrequent, light spotting. A smaller group deals with prolonged or frequent bleeding that can be frustrating.
There’s no reliable way to predict which pattern you’ll fall into before trying it. The good news is that for many users, bleeding becomes lighter and less frequent over time. If your bleeding pattern is bothersome, your provider can discuss short-term options to help manage it.
Weight Gain: What the Data Shows
Weight gain is one of the most common concerns people have about hormonal birth control, and it’s worth looking at what actually happens. A controlled study comparing over 200 implant users to a similar-sized group not using the implant found no significant difference in actual weight gain at one or three months. The implant group gained a median of 0.5 kg (about one pound) at three months, while the control group gained nothing, and statistically, the difference wasn’t meaningful.
What was different, though, was perception. About 15% of implant users reported feeling like they’d gained weight, compared to just 4% in the control group. This gap between perceived and measured weight change suggests the implant may cause bloating or body composition shifts that feel like weight gain without a significant change on the scale.
Medications That Can Reduce Effectiveness
Certain medications can speed up how quickly your body breaks down the implant’s hormone, potentially making it less effective. The most notable include some seizure medications (such as carbamazepine, phenytoin, and topiramate), the antibiotic rifampin, the herbal supplement St. John’s wort, and certain medications used to treat HIV or hepatitis C.
If you need to take any of these, you don’t necessarily have to remove the implant. But you should use a backup method like condoms while taking the medication and for 28 days after stopping it, since the effect on the implant’s hormone levels can linger that long.
Rare but Serious Risks
Serious complications are uncommon but worth knowing about. In rare cases, an implant can migrate from the insertion site. The UK’s medicines regulator identified 126 reports of migration up to mid-2019, with 18 of those involving movement to the lung area. Worldwide, 107 cases of migration to the chest or pulmonary artery were identified over roughly two decades of the implant being on the market. Given the millions of implants placed during that period, this is an extremely rare event. Updated guidelines now specify a precise insertion site on the inner upper arm to minimize this risk.
If you can’t feel your implant where it was placed, or if you develop unexplained shortness of breath, contact your provider. In most cases, though, the implant stays exactly where it was put.
Fertility After Removal
Removal is a quick procedure, typically faster than insertion. Your provider numbs the area, makes a tiny incision, and slides the rod out. Unlike some long-acting methods that can delay the return of fertility for months, the implant clears your system rapidly. It’s possible to get pregnant almost immediately after removal, so if you’re not ready for that, have another contraceptive method lined up before you get it taken out.