Injection: depot medroxyprogesterone acetate (DMPA)
Depot medroxyprogesterone acetate (DMPA) is a synthetic long-acting form of the hormone progesterone. DMPA is similar to the birth-control minipill in that it does not contain estrogen. Like other progesterone-based contraceptives, DMPA acts by preventing the release of the egg from the ovary (ovulation) and by promoting thick cervical mucus that impedes the sperm's progress. Its effectiveness in preventing pregnancy is close to 100%.
DMPA must be injected by a health care professional every three months (12 weeks). It is administered as a deep muscle (intramuscular) injection. A lower-dose formulation of the drug that is injected beneath the skin (subcutaneously) is also available. The injection must be administered within the first 5 days of a woman's menstrual period. She is then protected from pregnancy within 24 hours of receiving the injection.
A woman may stop having periods altogether after using DMPA for one year. After two years of use, 70% of women will have no menstrual bleeding. Menstrual periods stop because the DMPA causes the ovaries to go into a "resting" state. When the ovaries do not release an egg every month, the regular growth of the lining of the uterus does not occur and no uterine lining is shed during the subsequent menstrual cycle.
A woman's menstrual periods should begin again within six to 18 months after she stops taking the injections. A woman can also become pregnant, usually within 12 to 18 months, once she stops using DMPA. If a new mother does not breastfeed her baby, she can resume the injections right after childbirth. Mothers who are breastfeeding can safely begin the injections six weeks after childbirth. The injections do not reduce the flow of her breast milk, and no harmful effects on the baby have been noted.
The most common side effects of DMPA injections are irregular menstrual cycles, cessation of menstrual periods, and weight gain. Other side effects may include nervousness, dizziness, stomach discomfort, headaches, fatigue, or breast tenderness. It is important that a woman realize that once she has been injected with DMPA, any side effects she may experience cannot be neutralized or eliminated. She has to tolerate these side effects until the medication wears off, typically three months later.
DMPA has also been shown to have a negative effect on bone mineral density, especially with longer-term use; however, studies have shown that her previous bone density is usually restored when the drug is discontinued.
Women may be able to use DMPA when avoidance of estrogen is prudent for medical reasons (see oral contraceptives). A qualified health care provider should be able to help make the proper distinction. DMPA should not be used by women who have a history of breast cancer, blood clots, liver disease, unexplained vaginal bleeding, or stroke. A woman on DMPA should contact her health care professional if she experiences a heavy menstrual flow, severe abdominal pain, headaches, or depression.
DMPA injections are over 99% effective if the injections are received according to the correct schedule. A woman using injection contraceptives has the advantage of being capable of becoming pregnant at a later time, if desired, simply by discontinuing use. DMPA does not increase a woman's risk of cancer, including breast cancer, and greatly reduces her risk of developing uterine cancer.
Injectable hormonal contraceptives do not protect against sexually transmitted infections.