Nexplanon is a birth control implant that lasts for up to 3 years and is over 99% effective. Nexplanon is a small, thin and flexible arm implant that is placed under the skin of your inner, upper arm. It is reversible and can be removed at any time during the 3 year period. Nexplanon must be removed by the end of the third year and may be replaced by a new implant at the time of removal. The most common side effect of Nexplanon is a change in your normal menstrual bleeding pattern. In studies, 1 in 10 women stopped using Nexplanon because of an unfavorable change in their bleeding pattern.