Progestin Implant (Implanon and Nexplanon)

Effectiveness: More than 99 percent effective (less than 1 pregnancy per 100 women each year). Effectiveness has not been tested on extremely overweight or obese women.

What is it? A flexible plastic rod, about the size of a cardboard matchstick, is inserted by a clinician under the skin of your upper inner arm. It slowly releases progestin, a synthetic version the body's hormone progesterone. Implanon lasts 3 years but can be removed by your clinician at any time.

How does it work? Like birth control pills, it uses hormones to prevent the ovaries from releasing an egg. It also prevents fertilization by affecting the lining of uterus and thickening the cervical mucus.

STD protection: No; you will still need to use condoms if you are concerned about STDs.

Benefits: It gives long-lasting birth control, which allows you to feel more spontaneous about having sex. You don't have to remember to use daily birth control or to interrupt foreplay to use birth control. It can be used if you are breastfeeding or cannot take estrogen. The rod usually is not visible. Your periods are likely to become lighter and fewer, and about one-third of implant users stop having periods after a year.