Depot medroxyprogesterone acetate (DMPA) is a long-acting, progestin-only hormonal contraceptive, widely known by its brand name, Depo-Provera. This injectable medication is administered by a healthcare professional every few months to prevent pregnancy. Its formulation provides a slow release of the hormone, offering continuous contraceptive protection without requiring daily action from the user.
Mechanism of Action
DMPA prevents pregnancy by targeting the hormonal signals of the reproductive cycle. Its primary function is to suppress ovulation, the monthly release of an egg from the ovary. It achieves this by inhibiting the secretion of gonadotropins from the pituitary gland, the hormones responsible for triggering an egg’s maturation and release.
The contraceptive also thickens cervical mucus, creating a physical barrier that makes it difficult for sperm to travel through the cervix. A third mechanism involves thinning the uterine lining, or endometrium. This change makes the lining less receptive, so in the unlikely event that fertilization occurs, it is very difficult for an embryo to implant.
Administration and Efficacy
DMPA is administered by a healthcare provider as an injection every 12 to 13 weeks. The injection can be given deep into a muscle (intramuscular), such as in the gluteal or deltoid muscle, or just under the skin (subcutaneous).
When used exactly as directed (“perfect use”), DMPA is over 99% effective at preventing pregnancy. In typical use, its effectiveness is closer to 96%, with the difference primarily due to not receiving injections on schedule.
To ensure a person is not pregnant when starting, the first dose is often timed with their menstrual cycle. It is administered within the first seven days of a period’s start or within seven days of an abortion. For postpartum individuals not breastfeeding, it can be given within four weeks of delivery.
Common Side Effects and Bodily Changes
Menstrual irregularities are the most common side effect of DMPA. During the first year, many individuals report unpredictable bleeding and spotting, which tends to decrease over time. With continued use, many find their periods stop altogether (amenorrhea). After one year, about 57% of users experience amenorrhea, rising to 68% after two years.
Other reported side effects include headaches, mood alterations, breast tenderness, and a decrease in libido. Weight gain is also linked to DMPA use, with studies showing an average gain of around 8 pounds over two years for some users. This change is believed to be connected to the medication’s influence on metabolism and appetite, and some may also experience fluid retention.
Bone Mineral Density Considerations
The use of DMPA is associated with a loss of bone mineral density (BMD), which prompted the U.S. Food and Drug Administration (FDA) to issue a black box warning for the product. This reduction in BMD is linked to the lower estrogen levels that result from using DMPA.
The amount of bone density loss is related to the duration of use. This is a concern for adolescents and young adults, as it may impact their peak bone mass. For this reason, healthcare providers may recommend against using DMPA for more than two years unless other contraceptive methods are unsuitable.
Fortunately, the loss of bone density is largely reversible after a person stops the injections and the ovaries resume normal estrogen production. One study in adolescents found that the return to baseline BMD values required an average of 1.2 years for the lumbar spine and up to 4.6 years for the hip.
Discontinuation and Return to Fertility
When an individual decides to stop using DMPA, the return to fertility is often not immediate. The effects of the injection can linger, leading to a potential delay in the ability to conceive. This is a significant consideration for those planning a future pregnancy.
The timeline for the return of fertility varies widely among individuals and does not appear to be related to how long the person used the contraceptive. The median time to conception is about 10 months following the final injection, though it can take up to 18 months or longer for others.
About 83% of former users who wish to become pregnant will conceive within 15 months of their last injection. Menstrual cycles may also remain irregular for up to 18 months after stopping. Despite the delay, there is no evidence to suggest that DMPA causes permanent infertility.