Birth Control Shot: 7 Facts an Ob/Gyn Wants You to Know

This injection protects against pregnancy for 3 months at a time.

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While the Pill still remains one of the most common birth control methods, more and more people are turning to easier options—that is, birth control methods that last longer and are more effective at preventing pregnancy.

One such method is the shot, also known by the brand name Depo-Provera. “The birth control shot is an injection of the hormone progestin that protects against pregnancy for three months at a time,” says Kecia Gaither, MD, director of perinatal services at Lincoln Medical and Mental Health Center.

Looking for a new birth control option? Here’s what you need to know before starting the shot:

1. You only need to think about it every three months.

Unlike the Pill, you don’t have to think about the shot every single day. You only need to make sure you visit the doctor every three months to receive the shot, which goes in your upper arm or butt. Some health centers may also provide the shot for you to take home and give to yourself.

2. The shot works like other progestin-only birth control methods.

Like the birth control implant and the hormonal IUD, the shot contains only progestin—as opposed to a combination of progestin and estrogen found in other forms of birth control. “Progestin thickens cervical mucus, and makes it harder for sperm to enter the uterus and fertilize the egg,” says Dr. Gaither.

Additionally, progestin thins the lining of the uterus, which prevents the egg from attaching to the uterine wall. Some people on the shot or other progestin-only birth control options may not ovulate at all—meaning no egg is released.

3. The shot is 94 percent effective at preventing pregnancy. 

This statistic takes into account human error—such as not getting the shot on time after three months. When the shot is used correctly, it’s actually 99 percent effective, according to Dr. Gaither.

“If you’re more than two weeks late for an injection, you may need to get a pregnancy test before the shot to play it safe,” says Dr. Gaither.

Keep in mind that the shot only protects against pregnancy. It is not meant to protect against sexually transmitted diseases, so you may still want to use condoms to protect against STDs.

4. Don’t use the shot if you want to get pregnant right away after you stop.

Some birth control methods allow pregnancy immediately after discontinuing use. For example, after taking out an IUD, you can essentially get pregnant right away.

The shot is different, at least for some women. “It is possible to get pregnant as soon as 12 weeks following the last injection,” says Dr. Gaither. “Though for some, it can take nine months or longer for fertility to return.”

5. The shot may affect your period.

Many types of hormonal birth control can alter your period, and the shot is no different. It varies from person to person, but you may notice one or more of the following changes after starting the shot:

  • Irregular bleeding

  • Lighter periods

  • No periods at all

  • And fewer menstrual cramps.

In fact, some people specifically use the shot and other hormonal birth control methods specifically to ease severe menstrual cramps or heavy, painful periods.

6. The shot may affect bone health.

“Studies have found that the shot decreases bone mineral density while you use it, so women shouldn’t use it for more than two years,” says Dr. Gaither. At that point, it might be wise to switch to a different birth control method.

Either way, it’s a good idea for all women to adopt habits that reduce their risk of osteoporosis. This includes making sure your diet includes enough calcium and vitamin D, and doing plenty of weight-bearing exercises to keep bones strong.

7. The shot may affect weight.

The majority of people who try the shot for birth control do not notice any changes to their weight. One study, however, did show that about a quarter of the women gained 5 percent of their starting weight within the first six months.

“If you’re someone who’s concerned about gaining weight, talk to your doctor about the best birth control option for you,” says Dr. Gaither.