Implanon is a single-rod hormonal implant that contains etonogestrel (a synthetic progestin). As with Jadelle and Sino-implant (II), it is one of the most highly effective contraceptive methods. Although Implanon is labeled for three years of use, data from numerous clinical trials reveal zero pregnancies through up to four years of use of Implanon.
Implants work by releasing a small amount of hormone steadily into the blood. This prevents pregnancy by thickening the cervical mucus, which blocks the sperm from meeting an egg, and by preventing ovulation to various degrees. However, Implanon prevents ovulation in every cycle throughout almost the entire three years of its labeled length of use. Because it prevents ovulation so well, users of Implanon are more likely to experience amenorrhea or infrequent bleeding than users of Jadelle or Sino-implant (II), which contain a different hormone (levonorgestrel). In contrast, users of Jadelle or Sino-implant (II) are more likely to experience irregular bleeding and frequent bleeding and spotting.