- The birth control shot deposits a synthetic progestin hormone into a muscle in the upper arm or buttocks. This hormone is called medroxyprogesterone acetate and it is slowly released into the blood stream over 11 to 14 weeks. This hormone prevents ovulation so there is no egg for sperm to fertilize. The hormone also thins the lining of the uterine wall and thickens the cervical mucus, which makes it harder for sperm to travel to the fallopian tubes.
- The birth control shot is considered highly effective when used correctly. Out of every 100 women who use the birth control shot, three or fewer will become pregnant. The birth control shot is most effective when the shots are properly scheduled 12 weeks apart. There is less room for error with the birth control shot since a daily medication is not required.
- One dose of Depo-Provera offers roughly three months of protection against pregnancy, which is beneficial for women who do not want to take medication each day. Menstrual periods are generally lighter or stop after several injections, which may be beneficial for some women. Also, the birth control shot does not contain estrogen, a hormone that can increase the risk of blood clots. This may be beneficial for women who have cardiovascular disease.
- The hormones contained in the birth control shot may have a number of side effects, including the interruption of the menstrual cycle. Some women may experience heavy bleeding or spotting between cycles during the first few months of use. Other reported side effects include weight gain, depression and sore breasts. The injection site may become sore, and lumps may appear in the skin. According to Pfizer, Depo-Provera may also contribute to bone density loss during use. Bone density returns after the woman stops getting the shot.
- While the birth control shot is generally effective in protecting against pregnancy, any pregnancy that does occur while on the shot has an elevated risk for complications such as miscarriage or birth defects. The pregnancy has a higher risk of being ectopic, meaning the embryo attaches itself to something other than the uterine wall. Also, it can take up to one year for fertility to return after the last Depo- Provera shot. Women who wish to become pregnant in the near future may want to consider an alternate form of birth control.
