It is a progestin that is also used in combination with ethinylestradiol, an estrogen, as a vaginal ring under the brand names NuvaRing and Circlet.

[15] Side effects of etonogestrel include menstrual irregularities, breast tenderness, mood changes, acne, headaches, vaginitis, and others.

[16] It works by stopping ovulation, thickening the mucus around the opening of the cervix, and altering the lining of the uterus.

[22] The failure rate of the implants is 0.05% for both perfect use and typical use because the method requires no user action after placement.

[35] Efavirenz, an inducer of the liver enzyme CYP3A4, appears to decrease etonogestrel levels[36] and increase rates of undesired pregnancy among implant users.

The opposite is true of CYP3A4 inhibitors such as ketoconazole, itraconazole and clarithromycin: they might increase etonogestrel concentrations in the body.

[35] Nexplanon/Implanon consists of a single rod made of ethylene vinylacetate copolymer that is 4 cm long and 2 mm in diameter.

[37] Serum levels maintain relatively stable through 36 months, which implies that the method may be effective for longer than three years.

[24] A needle-like applicator is used to insert the rod under the skin into the subdermal tissue on the inner side of the arm posterior to the groove between the biceps and triceps muscles.

If a woman receives an implant outside the first five days of her period, she should wait to have sex or use a backup method of contraception (such as a condom, female condom, diaphragm, sponge, or emergency contraception) for the following week after insertion to prevent pregnancy.

However, if the implant is inserted during the first five days of a woman's period, the drug typically is effective for that cycle and beyond.

[25][26] Within a week of removal, the hormones from the device leave the body and etonogestrel is undetectable in most users.

[45] Intermediate dose progestin-only contraceptives like Nexplanon or Implanon allow some follicular development but inhibit ovulation in almost all cycles as the primary mechanism of action.

A secondary mechanism of action is the progestogenic increase in cervical mucus viscosity which inhibits sperm penetration.

[16] It is less androgenic than levonorgestrel and norethisterone,[48][49] and it does not cause a decrease in sex hormone-binding globulin levels.

[16] Some inhibition of 5α-reductase and hepatic cytochrome P450 enzymes has been observed with etonogestrel in vitro, similarly to other 19-nortestosterone progestins.

[4][5] Steady-state levels of etonogestrel are achieved within one week upon insertion as an implant or vaginal ring.

[4][5] Following removal of an etonogestrel-containing implant, levels of the medication were below the limits of assay detection by one week.

[1] The possibility of the subdermal contraceptive implant began when silicone was discovered in the 1940s and found to be bio-compatible with the human body.

[57] In 1966 Dziuk and Cook published a study that looked at release rates and suggested that the rods could be well suited for contraception.

[58] After a study that used implants with progestogens for contraception, the Population Council developed and patented Norplant and Jadelle.

In 1990 De Nijs patented a co-axial extrusion technique of ethylene vinylacetate copolymers and 3-keto-desogestrel (etonogestrel) for the preparation of long-acting contraceptive devices, such as Implanon, Nexplanon and Nuvaring.

[60] The single rods were less visible under the skin and used etonogestrel as opposed to levonorgestrel in the hopes that it would reduce side effects.

Although Jadelle was approved by the FDA, it has never been marketed in the United States, but it is widely used in Africa and Asia.

[18][19] Nexplanon was developed to eliminate the problem of non-insertion and localization of Implanon by changing the inserter device and making the rod radiopaque.