What is the birth control shot and how does it work?

The birth control shot—also commonly known by its brand name, Depo-Provera®—is a reliable and low-maintenance option for preventing pregnancy. 

It’s an injection you receive once every three months, and it works by releasing a hormone that stops ovulation (when your ovaries release an egg). No ovulation means there’s no egg for sperm to fertilize, which makes pregnancy much less likely.

Many people choose the shot for its convenience. There’s no daily pill to remember and no ring or patch to place. Just a quick injection every 12 weeks and you’re good to go. It’s discreet, simple, and effective—making it a great fit for those who want a longer-term birth control option without needing to think about it every day.

What is the birth control shot?

The birth control shot is a convenient, injectable form of contraception that uses synthetic hormones to prevent pregnancy. Most healthcare providers recommend Depo Provera® for people looking for a reliable, hormone-based birth control shot. It’s given as an injection—usually in your arm, thigh, or buttocks—every 12 to 13 weeks.

Think of it as a quick quarterly injection for pregnancy prevention. Unlike daily pills or monthly rings, you only need to think about your birth control four times a year. The shot contains medroxyprogesterone acetate, a synthetic form of the hormone progestin, which your body naturally produces.

What makes this method stand out is its simplicity. There’s no need to interrupt intimate moments or remember a daily pill. The shot offers discreet, ongoing protection without daily effort. Depo Provera® is a trusted and popular birth control method.

The injection itself is quick and usually causes minimal discomfort. Some people even choose to self-inject at home, which adds another layer of convenience for busy schedules. The version that you can administer yourself at home is called Depo-SubQ Provera® 104. Each dose of the birth control shot provides three months of continuous pregnancy protection, giving you peace of mind without the hassle of daily maintenance.

How the control shot prevents pregnancy

The birth control shot works in several ways to provide effective pregnancy prevention.

When you get the injection, it releases a steady dose of synthetic progestin into your bloodstream that lasts about three months. This hormone creates changes in your body that make pregnancy very unlikely during that time.

What helps make the shot effective is that it doesn’t rely on just one mechanism—it works on multiple fronts to block pregnancy. Depo-SubQ Provera® 104 offers effectiveness of about 94%.

Your body responds to the hormone by making changes that last throughout those three months. These effects are fully reversible after you stop the shots, but while you’re using this method, it provides reliable protection against unplanned pregnancy. Note that the longer you use the shot, the longer you may have to wait until you are able to conceive. 

The role of progestin

Progestin is the key player behind the Depo-Provera® shot. It’s a synthetic version of progesterone, a hormone your body naturally produces during the second half of your menstrual cycle. When progestin is introduced consistently through the shot, it signals your body that it’s already pregnant (even though you are not pregnant).

This signal suppresses the release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) from your brain’s pituitary gland. Without these hormones, your ovaries don’t get the message to release an egg each month. No egg means no fertilization can happen—even if sperm are present.

Effects on cervical mucus and ovulation

Another important way the shot works is by thickening cervical mucus. Normally, around ovulation, cervical mucus thins out to help sperm swim through. Progestin keeps this mucus thick and sticky throughout the month, creating a barrier that’s very difficult for sperm to pass.

Suppressing ovulation is the primary way the shot prevents pregnancy. Most people on the shot don’t ovulate at all, though a small number may occasionally release an egg. Even then, other protections like thickened cervical mucus are still in place to prevent pregnancy.

Getting the Depo-Provera® shot

Starting the Depo-Provera® shot is simple. You’ll have an initial consultation with a healthcare provider, answering dynamic questions about your medical history and current health status. Learning about any health conditions, medications you’re taking, your pregnancy goals, etc., helps the provider determine your options.

If Depo-Provera® is right for you, your first injection can be administered at any point during your menstrual cycle. If you get it within the first five days of your period, you’re protected from pregnancy right away. If it’s later than that, you’ll need to use backup contraception—like condoms—for seven days while the hormones kick in.

For ongoing use, Depo-SubQ Provera® 104 is a popular choice because it only requires one shot every three months. Many people like not having to think about birth control daily or monthly. The injection can be given at a medical office, clinic, or even at home if you’re using the subcutaneous version.

How often to get the shot

The birth control shot is scheduled every 12 to 13 weeks. It’s helpful to mark your calendar or set a phone reminder because staying on schedule is important. You have a two-week window to get your next shot—anytime between weeks 11 and 13 after your last injection.

If you’re late past the 13-week mark, your provider may ask you to take a pregnancy test first. They might also suggest using backup contraception until your new shot has had time to work. Keeping up with your schedule ensures continuous protection without gaps.

What to expect during your visit

Appointments for the shot are usually quick and straightforward. Your provider will check in about any health changes since your last visit and may take your weight and blood pressure. They’ll also confirm you’re not pregnant before giving the injection.

The injection itself takes just a few seconds. You might feel a quick pinch or sting, similar to any routine shot. Some people notice mild soreness at the injection site for a day or two afterward. To keep things comfortable, your provider may recommend rotating injection sites each time.

Possible side effects of the birth control shot

Like any medication, the birth control shot can cause side effects. Most people tolerate it well, but it’s important to know what to expect. Side effects often show up during the first few months and may ease as your body adjusts to the hormones.

The most common side effects include changes in your menstrual cycle, mood shifts, headaches, or breast tenderness. Keep in mind, not everyone experiences side effects—and many people use the shot comfortably for years.

Because the hormones stay in your system for the full three months after each injection, side effects aren’t reversible right away, like they can be with pills. That’s why it’s especially important to talk through potential side effects with your healthcare provider before starting.

Weight gain and other body changes

Weight gain is one of the most talked-about side effects of the birth control shot. It’s common to gain a few pounds during the first year of use. However, this doesn’t happen to everyone, and for many, the weight stabilizes after the initial adjustment.

This gain may be linked more to increased appetite than to changes in metabolism. Being mindful of your eating habits and keeping up with regular physical activity can help manage this. 

Despite this possibility, many people choose the shot for its convenience and effectiveness—and find it worth it.

Changes in menstrual cycle and vaginal bleeding

The shot can significantly change your menstrual cycle. Many people notice irregular bleeding or spotting, especially in the first few months. This might mean lighter periods, unpredictable bleeding, or spotting between cycles as your body adjusts.

After about a year of use, roughly half of users stop having periods altogether. While that might sound concerning, it’s safe and reversible. The absence of periods doesn’t mean pregnancy or a problem—it’s just how the shot affects the lining of your uterus.

Lowered bone density

One important factor to be aware of is the shot’s effect on bone density. Long-term use may lower bone mineral density, especially in younger people whose bones are still developing. The good news is that this loss is generally reversible after stopping the shot.

Healthcare providers often recommend calcium and vitamin D supplements during use, and weight-bearing exercise can also support bone strength. For most people, the benefits of a highly effective birth control method outweigh these risks—but it’s an important part of the conversation with your provider.

Risks and who should avoid the birth control shot

The birth control shot is safe for most people, but certain health conditions mean it might not be the best choice for you. Knowing these risk factors helps make sure your birth control fits your health needs. Your healthcare provider will review your medical history carefully and only offer  the shot if it is a good option for you.

For some people, other contraceptive options may be safer. Birth control isn’t just about preventing pregnancy—it’s about doing so while protecting your overall health. When risks of the shot outweigh benefits, your provider will help you explore alternatives.

Age also matters. For example, women approaching menopause may need special attention because of potential effects on bone density. Your provider will consider these factors alongside your preferences and contraceptive goals.

Risk factors to watch for

The birth control shot isn’t recommended if you have:

• Unexplained vaginal bleeding
• Known or suspected pregnancy
• Liver disease
• History of breast cancer
• Severe cardiovascular disease
• High risk of osteoporosis

If you’re dealing with current depression or have a history of severe depression, it’s important to discuss this with your provider. Some people notice mood changes or worsening depression when using the shot. Being open about your mental health helps your provider support you in finding the best option.

Protection against sexually transmitted infections

It’s important to know that the birth control shot does not protect against sexually transmitted infections (STIs). While it’s highly effective at preventing pregnancy, it doesn’t create a physical barrier against infections like HIV, chlamydia, gonorrhea, or herpes.

If you’re not in a mutually monogamous relationship with a tested partner, using condoms is essential. Condoms are the best way to reduce your risk of STIs. Using condoms alongside the Depo-Provera® shot gives you dual protection: reliable pregnancy prevention and STI risk reduction.

Why the birth control shot might be right for you

The birth control shot offers a unique blend of effectiveness, convenience, and privacy that makes it a great option for many people. With just four injections a year, it removes the daily hassle of birth control while providing about 94% effectiveness with typical use. Whether you choose the traditional injection or the newer Depo-SubQ Provera® 104 (which you can even give yourself at home) you’re choosing a method trusted by millions worldwide.

Knowing how the shot works—how it affects ovulation, cervical mucus, bone health, and fertility return—helps you make an informed choice that fits your body and your life. While side effects like weight gain or changes to your menstrual cycle affect some people, many find these manageable alongside the shot’s benefits.

Nurx makes it easy to access these options and put control of your reproductive health right in your hands.

Ready to explore if the Depo-SubQ Provera® 104 shot is right for you? Connect with a Nurx provider today to get personalized guidance and easy access—birth control made simple, on your schedule.

Frequently Asked Questions (FAQ):

Is the birth control shot a good method of contraception?

Yes. It’s highly effective, with a typical use effectiveness rate of about 94%.

What are the disadvantages of the birth control shot?

You’ll need an injection every 3 months, and some users experience side effects like weight gain and irregular periods.

How effective is the Depo-Provera® shot in preventing pregnancy?

With perfect use, it’s about 99% effective; typical use effectiveness is around 94%.

Does the Depo-Provera® shot cause weight gain?

Some users may gain weight, typically 5-11 pounds in the first year, though experiences vary.

The information provided is not a substitute for professional medical advice, diagnosis, or treatment. You should not rely upon this content for medical advice. If you have any questions or concerns, please talk to a medical professional.

Services not offered in every state. Medications prescribed only if clinically appropriate, based on completion of  required consultation. Individual results may vary.

If you’re experiencing a mental health crisis, please call 911 or  go to your nearest emergency department. If you are contemplating suicide, call 911 or call/text the National Suicide and Crisis Lifeline at 988. These services are available 24/7.

Depo-SubQ Provera® 104 may be prescribed by a Nurx affiliated provider but is not fulfilled through a Nurx pharmacy. Learn more about Depo-SubQ Provera® here.