Here is what the Bedsider.org says about them:

The implant (Implanon or Nexplanon are the brand names) is a teeny-tiny rod that's inserted under the skin of your upper arm. It's so small, in fact, most people can't see it once it's inserted—which means it can be your little secret, if you're so inclined. The implant releases hormones that keep your ovaries from releasing eggs and thicken your cervical mucus, which helps to block sperm from getting to the egg in the first place. Plus, it prevents pregnancy for three years.

Here's how the whole thing goes: You visit a health care provider, they gather all your medical info and give you a physical exam, then they numb a small area of your upper arm with a painkiller and insert the implant under your skin. And you're done.

If you get the implant during the first five days of your period, lucky you: You're set with pregnancy protection from that very moment. If you're outside of those first five days, you'll need to use a back up method for the following week.

When it's time to take the implant out, your provider will numb your arm again, make a tiny cut in your skin, and remove the implant. If you're interested in continuing to use the implant, they can put another one in at the same time.

Endometriosis