The Nexplanon implant is a small, flexible, and hormone-releasing rod that is inserted under the skin of the upper arm to provide long-term birth control. It works by releasing a steady dose of the hormone etonogestrel, which prevents ovulation, thickens cervical mucus, and thins the uterine lining, making it difficult for sperm to reach an egg and for a fertilized egg to implant in the uterus.