context: Birth control implants are devices that go under a woman's skin. They release a hormone that prevents pregnancy. The implant available in the U. S. is Nexplanon. It's a newer version of the implant Implanon. You might hear people call them arm bars. The implant is a plastic rod about the size of a matchstick. It contains a form of the hormone progesterone called etonogestrel. Once the implant is placed under your skin, it releases small amounts of etonogestrel. The hormone works on your pituitary gland, which tells your ovaries not to release eggs. It also makes the mucus in your cervix thicker. This makes it harder for sperm to get to any eggs that are released. Hormonal implants work more than 99% of the time. How do they stack up to other birth control methods? Intra-uterine devices ( IUDs) are also 99% effective. Birth control injections are 94% effective. The pill is 91% effective. But none of these methods protect you from sexually transmitted diseases ( STDs). Only condoms prevent STDs. You can use a birth control implant for up to 3 years. Then you need to get it replaced. As with any type of birth control method, implants have pros and cons. Advantages include: They work. Fewer than 1 in 100 women using an implant will get pregnant each year. Easy to use. Unlike some birth control options -- like condoms, patches, shots, rings, and pills -- the implant works no matter what. You don't have to worry about using it incorrectly or remembering to replace or take it often. Fast reversal. If you want to get pregnant, you can get started on that right after you get the implant taken out. Less painful periods. In studies of women using implants, painful periods got better. Lighter or no periods. Your period might get shorter, or even stop completely. Some problems with birth control implants include: Cost. You may have to pay about $600 or more for an exam and the implant, and $100 or more to have it removed. No protection against STDs. Birth control implants won't prevent HIV or any sexually transmitted diseases. Use a condom for that. Possible side effects include problems from putting the implant in, like: Pain Bruising or swelling Redness Infection Scarring Other possible side effects include: Irregular menstrual bleeding Depression and other mood changes Weight gain Abdominal pain or nausea Acne Breast pain, back pain, or headaches Vaginitis Dizziness Noncancerous ovarian cysts Your doctor or another health care professional will inject medicine to numb your skin on your upper arm, where you'll get the implant. That may sting a bit. Then they'll use a tool that pushes the rod in through a needle. That won't hurt. It feels like a little bit of tugging. The process may take less than a minute. Afterward, you should be able to feel the implant under your skin but not see it. Taking out the implant is quick and simple. Don't try to do it yourself. Your doctor needs to remove it. While you're in the office they'll: Mark the spot on your arm where the implant is Clean the area to prevent infection Give you a shot with medicine to numb the site Make a small cut at the top of the implant and remove it It could take as long as 20 minutes if there's a lot of scar tissue in the area. If the doctor can't easily find the implant, they might take an X-ray to locate it. Your arm might be sore after the implant comes out. You'll need to: Wear a bandage for 48 hours Keep the area dry for 24 hours You shouldn't use birth control implants if you think you may already be pregnant or you have: Sensitivity to any part of the implant Unexplained vaginal bleeding Breast cancer (now or in the past) Liver disease or liver tumors History of blood clots (deep vein thrombosis) Use it with caution if you have: Diabetes High cholesterol Seizure disorder You've ever had depression. Also, the implants may not work as well if you're very overweight. Some medications can make birth control implants less effective. Ask your doctor about that.