Hormone implants are soft capsules containing the hormone progestin. The capsules are inserted under the skin of a woman’s upper arm by a doctor who has been trained in this procedure. For up to 5 years the capsules release a steady, low dose of progestin to block ovulation (release of an egg from an ovary). Hormone implants are a highly effective means of birth control. The most common side effect is irregular periods. Also, removing the implant may be difficult and painful.
Injectable contraceptives contain the female hormone progestin. They are injected by a physician at regular intervals, usually about every 3 months. Injectable contraceptives prevent sperm from reaching the uterus by thickening the mucus that covers the cervix. Some doctors consider this to be the most effective reversible contraceptive method available. The most common side effect is irregular menstrual periods. Injectable contraceptives also have positive health effects—an increase in blood iron levels as well as protection against pelvic inflammatory disease, ovarian cancer, and endometrial cancer.