Before discussing Implanon, let’s review the hormones your body produces and hormonal birth control methods. Your body produces estrogen and progesterone. Birth control pills and NuvaRing (inserted in the vagina for 3 weeks) contain both estrogen and progesterone. There are 3 methods that contain only progesterone: the shot, Mirena (intra-uterine device or IUD) and Implanon.

How do these hormonal methods work? They prevent the release of eggs from your ovaries and change the mucus in your cervix making it more difficult for the sperm to get to the egg. They also change the lining of the uterus making it more difficult for a fertilized egg to attach itself to the uterus.

What is Implanon? It is a small, thin rod that is inserted just under the skin in the upper arm (underside). It is etonogestrel, a type of progesterone (or progestin). Although it was only approved for use in the U.S. in 2006, it’s been used in 13 countries for many years. Its contraceptive effect lasts for 3 years, after which it is removed and another one inserted.

How effective is it? Implanon is more than 99% effective. Side effects? The most common side effect is a change in your menstrual cycle. You may have no periods, less bleeding, more bleeding, or spotting. There tends to be more bleeding in the first 6 months, but it lessens over time. Some women who gained weight with the shot fear weight gain with Implanon. However, Implanon has a different type of progestin than the shot. The average weight gain with Implanon is quite small--3.7 lbs in 2 years.

The most serious complication with any hormonal method is blood clots. Who’s at risk for blood clots? If you are over 40 years old, smoke cigarettes, and have high blood pressure or diabetes, you are at risk for developing blood clots.