Everything You Need To Know about the Birth Control Shot
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Medically reviewed by Peter Weiss, MDMedically reviewed by Peter Weiss, MD
The birth control shot is a type of short-acting hormonal birth control method. Two types of birth control shots are approved by the U.S. Food and Drug Administration (FDA): Depo-Provera and Depo-SubQ Provera 104.
Both contain the hormone progestin and are given every three months. However, Depo-Provera is injected into a muscle, whereas Depo-SubQ Provera 104 is injected under your skin. Depo-SubQ Provera 104 contains a lower dose of progestin than Depo-Provera.
Progestin-only birth control injections are highly effective at preventing pregnancy—they are slightly more effective than progestin-only birth control pills. When people keep up with their shots, they have a less than 1 in 100 chance of getting pregnant within their first year of use.
How the Birth Control Shot Works
Birth control shots contain synthetic forms of progestin, a hormone that can stop you from getting pregnant. Synthetic progestin has multiple effects on your body, all of which stop pregnancy from occurring. Birth control shots:
Suppress ovulation (release of egg from your ovary)
Decrease the amount of cervical mucus you produce
Thicken your cervical mucus, which can prohibit sperm from entering your uterus
Thin out the lining of your uterus, which makes a pregnancy less likely to be established
Depending on the type of birth control shot you are using, you will need to be injected with it either in a muscle (usually the upper arm or buttock) or subcutaneously, meaning right beneath your skin (typically your thigh or abdomen).
You don’t administer the birth control shot yourself; your healthcare provider will do this. The shot should feel like a quick sting and generally won’t continue to be painful after administration.
Whatever type you are using, birth control shots are given every three months, or roughly every 13 weeks. It’s important to maintain this schedule to successfully prevent pregnancy.
Tips for Effectiveness
Here are some tips about timing and how to optimize the effectiveness of your birth control shot:
You can get the shot at any time in your cycle as long as you are sure you aren’t pregnant.
If you get your shot within the week after your period arrives, you don’t have to use additional birth control, such as condoms, for the rest of your cycle.
If you wait longer than a week after your period first arrived, you will need to use birth control for the next week to ensure you don’t get pregnant.
If you’ve been using a different type of birth control, you can stop using it when you get your first shot, but follow the above precautions to ensure you don’t get pregnant until the shot has become most effective.
Benefits
One of the biggest benefits of birth control shots is that they are convenient. While it’s important to keep up with your shot schedule (one shot roughly every three months), you don’t have to think about it on a daily basis.
Birth control shots are also highly effective at preventing pregnancy. With typical use—which might mean forgetting to get injections on time—six out of every 100 people get pregnant while using birth control shots. With perfect use—meaning you are receiving injections every three months according to the schedule set by your provider—one out of every 100 people will become pregnant.
Birth control shots are more effective than hormonal birth control pills. With typical use, nine out of every 100 people get pregnant while on the pill. Birth control shots also offer longer-lasting protection against pregnancy than other similar methods, like birth control pills, transdermal birth control patches, and vaginal rings.
Although the main benefit of birth control injections is pregnancy prevention, they also have some other health benefits. These include:
A reduced risk of uterine cancer if used on a long-term basis
Reduced pain caused by endometriosis
Potential reduction in sickle cell disease symptoms
Potential reduction in seizure disorder symptoms
Potential decrease in bleeding from uterine fibroids
Potential decreased risk of pelvic inflammatory disease (PID)
Side Effects of Birth Control Shot
Most people tolerate birth control shots well, but there are some potential side effects to be aware of. The two most common side effects are weight gain and irregular bleeding.
Weight Gain
It’s possible to experience weight gain when using the birth control shot. Typically, this weight gain is not significant—usually less than five pounds. Talk to your healthcare provider for guidance if you are concerned about weight gain after starting the shot.
Irregular Bleeding
You may also experience irregular bleeding and spotting, especially as your body adjusts to the shot. Research has found that about 57% of people experience irregular periods within the first year of taking the shot. By two years, this number decreases to between 10-30%.
Other Side Effects
Other less common side effects of the birth control shot include:
A delay in the return to fertility after stopping shots
Prolonged periods of no ovulation
Unintended pregnancy
Irregular thickening of uterine lining
Infections of the reproductive system
Vaginal cysts
Vaginal or uterine hemorrhage (bleeding)
Considerations and Precautions
Birth control shots are good options for many people, but they are not suitable for everyone.
While birth control shots are very effective at preventing pregnancy, they do not protect against sexually transmitted infections (STIs). This means that if you have sexual contact with a partner with an STI, you could contract the infection yourself if you don’t take further precautions. Precautions to consider include using a condom or a dental dam to protect against STIs.
Also, if you are someone who wants to get pregnant in the near future, birth control shots may not be the best choice. While you will regain fertility after stopping birth control shots, it can take about 10 months to conceive after stopping birth control shots. For some people, it may take more time.
People with certain risk factors should exercise extra caution and talk to their healthcare provider before taking birth control shots. These include risk factors include:
Cardiovascular disease
Diabetes
History of smoking
Older age
History of stroke
History of vascular disease
Elevated blood pressure that isn’t being managed
Lastly, birth control shots can cause temporary bone loss in certain individuals. This symptom is usually reversed after stopping birth control shots, but you may want to be mindful of your bone health while using the shot. Healthcare providers often recommend eating a diet high in calcium and vitamin D (or supplementing with these vitamins and minerals) while you're on the birth control shot.
A Quick Review
Birth control shots are a highly effective way to prevent pregnancy. They work by preventing ovulation and making the body a less hospitable environment to support pregnancy.
Although they are a good option for many people, there are some precautions to be aware of. Birth control shots can cause irregular bleeding in some people, don’t protect against STIs, and may cause temporary bone loss.
If you have further questions about whether birth control shots are right for you, please reach out to your healthcare provider.
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