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How Effective is the Birth Control Shot?

Some methods of birth control - like condoms and the combined pill - are more common than others. But that doesn’t necessarily mean that they’re the right method for you, or even the most effective. Today we’re going to take a look at the birth control shot. Here’s everything you need to know about what it is, how it works, and how effective it is.

What is the birth control shot?

The birth control shot, or injection, is a medium-term contraceptive method that is longer lasting than methods like condoms, but shorter-term than IUDs or implants.

It’s an injection that is given in your buttocks, upper arm, thigh or tummy, and depending on the brand used, it can last for as long as 13 weeks. The most commonly used brand in both the UK and USA is Depo-Provera, which lasts for 13 weeks, while other brands like Noristerat last for 8 weeks.

How does the birth control injection work?

The shot contains the hormone progestin, which is a synthetic version of the natural hormone progesterone. It prevents ovulation and thickens the cervical mucus, which stops sperm from getting through. Together, these two things prevent pregnancy. 

You can start using the birth control injection at any time in your cycle. If you get it in the first 7 days after starting your period, then you’ll be protected against pregnancy straight away. You’ll also be protected immediately if you get it within 7 days after a pregnancy has terminated, while if you get it within 3 weeks of giving birth, you’ll also have immediate protection.

If you get the shot at any other time in your cycle, you’ll need to use another form of birth control for one week to ensure you’re fully protected - and then after that, you won’t need to use a backup method. However, it’s important to remember that the birth control shot doesn’t protect against STIs, so depending on your situation, you may also want to use condoms.

How long does the birth control shot last?

As mentioned above, you’ll need to get the shot every 8-13 weeks, and it’s usually given by a nurse or doctor. It’s important to remember to make an appointment on time, as if you forget to get the shot within the correct time frame, you won’t be prevented from pregnancy. With some brands, you may be able to administer the shot at home yourself, but it’s best to speak to your nurse or doctor about all the options available to you.

Typical and perfect use: birth control shot effectiveness

When it comes to birth control effectiveness, we always look at it in terms of perfect and typical use. Perfect use refers to how effective a particular form of contraception is if it’s used perfectly, every single time. Typical use reflects the way it’s usually used, accounting for both user error and issues with the contraception itself.

When used perfectly, the shot is a highly effective form of hormonal birth control, with more than 99% effectiveness. That means that less than 1 person out of every 100 using this method of contraception will get pregnant each year.

However, with typical use, the birth control shot is around 94% effective - meaning that 6 in 100 people who get the shot will get pregnant in a year.

The difference in numbers between typical and perfect use is because some people forget to get their injections on time, meaning they’re not protected against pregnancy. So, if you choose to use this method, be sure to book your appointments (and remember to attend them!) as it significantly increases the effectiveness of this birth control method.

Benefits of birth control shot

If you’re someone who struggles to remember to take a pill every day, then the birth control shot could be a good option for you - you get it once and then can forget about it for the next couple of months. 

It also doesn’t interrupt sex, so it could be a good choice for you if you dislike other methods of birth control for this reason. 

It could also be a good choice for women who can’t use contraception that contains estrogen, and for some women, it can reduce heavy, painful periods and reduce premenstrual symptoms. Some women may even stop getting a period altogether - which can be an advantage for some women, while others prefer to have a regular monthly period.

Disadvantages of birth control shot

The birth control shot is a form of hormonal birth control, and therefor there’s a chance you may experience side effects, such as:

  • Changes to your period - you may bleed for longer, they may become irregular, shorter, or stop altogether
  • Spotting between periods
  • Nausea
  • Weight gain
  • Headaches
  • Breast tenderness
  • Mood swings

These side effects may last for 8-13 weeks (as long as the injection lasts), or they may settle down faster.

The birth control shot doesn’t protect you against STIs, so you may also need to use condoms when using the shot as your main method of birth control.

It may not be suitable for you if you’re planning on getting pregnant in the near future as it can affect your fertility for up to a year after you stop using it. If you’re planning to get pregnant soon after you stop using birth control, you should consider another method, such as Natural Cycle, can help you plan pregnancy too when the time is right.

More birth control options

Not sure if the injection is the right method of contraception for you? Luckily, there are plenty of options out there to choose from. There’s no such thing as one-size-fits-all when it comes to contraception, which is why it’s important to weigh up your options before switching birth control. Here are some more methods you might want to consider instead of the birth control shot.

The implant

Like the birth control shot, the implant is a method of hormonal birth control - but it lasts for longer than the injection. It’s a small plastic rod containing progestogen, that’s inserted into your upper arm. 

In much the same way as the shot, the hormones stop ovulation and thicken your cervical mucus to prevent pregnancy, and once fitted, it works for three years. That makes it a good option for anyone looking for a hormonal birth control method that they don’t need to think about on a daily, monthly or quarterly basis. The implant is more than 99% effective with perfect use.


Intrauterine devices or IUDs are small objects shaped like an upside-down anchor that sits inside the uterus. There are two kinds: hormonal and non-hormonal. The hormonal IUD works in the same way as the shot and the implant, by releasing a synthetic dose of the hormone progesterone to prevent pregnancy. Once fitted, it can be used for five years. 

The non-hormonal IUD contains copper instead of hormones. The copper creates a hostile environment for sperm survival. Typically a copper IUD lasts for five to ten years. Both kinds of IUD are more than 99% effective with perfect use.

Natural Cycles

If you’re looking for a non-hormonal method of birth control, then Natural Cycles could be a good option for you. In 2018, it became the first FDA cleared birth control app available in the US, and it works by using the basal body temperature method along with a smart algorithm that learns the patterns of your menstrual cycle, helping you to become aware of your own fertile window. On your red days - the days you are fertile - you should either abstain from sex or use condoms, to prevent pregnancy. Natural Cycles is 93% effective with typical use and it’s 98% effective with perfect use. 

Thinking about going hormone-free? Find out if Natural Cycles could work for you today.

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Written By

Lauren McKay

Lauren is an Edinburgh-based writer, yoga teacher, and advocate for driving women's health knowledge. When she's not at her laptop you'll find her in the yoga studio, running up a hill, or exploring Scotland's beautiful scenery.

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Scientifically Reviewed

Jack Pearson

Dr. Jack Pearson is Natural Cycles’ in-house medical expert. With 10+ years of experience working in the field of fertility, he dedicates the majority of his time to conducting groundbreaking research within the field of women's health.

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