The contraceptive injection
Reviewed by our clinical team
The contraceptive injection is a popular method of contraception that is very effective at preventing pregnancy. It also has other benefits such as stopping your periods and being a very convenient contraceptive option for those who don’t wish to take a pill everyday.
In this article we’ll share everything you need to know about the contraceptive injection including how it works, possible side effects and whether or not it may be the right method for you.
What is the contraceptive injection?
The contraceptive injection is a hormonal method of birth control, meaning it contains hormones (in this case progestogen) that help to prevent unwanted pregnancy.
The main difference is that it isn’t inserted into the vagina like the hormonal coil, placed in your arm like the implant or taken orally like a pill.
With perfect use (i.e. getting your jabs on time), the contraceptive injection is more than 99% effective - one of the highest rates of protection for long-term hormonal contraception methods. However it’s important to remember that the injection doesn’t protect you from STIs (you’ll need barrier methods such as condoms for that).
There are three types of contraceptive injection; Depo-Provera, Sayana Press and Noristerat. Depo-Provera is the most common method in the UK, however Sayana Press is becoming increasingly popular as it can be self-injected. Both last for 13 weeks whereas Noristerat only lasts for eight weeks.
Who can use the contraceptive injection?
Most women are eligible to get the contraceptive injection. It’s not affected by other medicines and is safe to use whilst breastfeeding or after giving birth.
The contraceptive injection is suitable for those who:
- Are sure they are not pregnant
- Are not planning to have a baby within the next 12 months
- Are happy if their menstrual cycle changes
- Do not have liver disease
- Have never had breast cancer
- Are not at risk of osteoporosis (bone disease)
- Do not have a phobia of needles
- Do not have a history of stroke, heart disease or arterial disease
- Do not experience unexplained bleeding after sex or between periods
How does the contraceptive injection work?
The contraceptive injection works to prevent pregnancy by steadily releasing the hormone progestogen into your bloodstream. This has three effects:
- It stops your body from ovulating (releasing an egg each month)
- It thickens the cervical mucus to make it harder for sperm to enter the womb
- And it also thins the lining of your womb, making it more difficult for a fertilised egg to implant itself
It is injected into your buttock, upper arm or (for Sayana Press) into your tummy or thigh.
The contraceptive injection begins to work immediately if you are within the first five days of your menstrual cycle. At any other point in your cycle, it will take seven days to be effective, so make sure to use additional contraception.
If you have just had a baby then you are also immediately protected from pregnancy (up to 21 days birth). Any later than 21 days and you’ll also need to use extra protection for the next seven days.
You can have the contraceptive injection immediately after an abortion or miscarriage. It will be effective straight away unless it has been more than five days, in which case you’ll need to use additional contraception such as condoms.
Contraceptive injection advantages
The contraceptive injection has many more benefits other than protecting you against pregnancy:
It’s a convenient option
You only need to get the injection every 8-13 weeks, making it much easier to remember than the pill. It also doesn’t interrupt sex, making it more reliable with typical use.
You may get lighter periods
Many women report getting lighter periods or no periods altogether whilst using the contraceptive injection.
It can be used during breastfeeding
The contraceptive injection is a safe method of hormonal contraception for after birth or whilst breastfeeding.
It isn’t affected by antibiotics
Other medicines including certain antibiotics have no impact on the effectiveness of the injection. It also isn’t impacted by vomiting or diarrhoea in case of illness.
Contraceptive injection side effects
Some women may experience side effects after having the contraceptive injection. These may include:
Irregular periods
For most women their periods will change: they usually become less regular and less predictable. The blood flow is likely to change as well, it can vary from light spotting to heavy bleeding. For some women the periods will stop altogether, whereas some women will continue to have normal periods. But don't worry: Your periods will go back to normal after stopping the injections. However, it can take up to one year for your cycles to get back to normal, so this is important to bear in mind when you are thinking of trying for a baby.
Weight
The evidence from studies looking into weight gain on the injection is conflicting, but out of all methods of contraception the injection is the most likely method to cause weight gain. This tends to be worse if yo are younger and your BMI is >30 or more to start with. The weight gain is likely due to fluid retention; it it also thought that it stimulates your appetite.
Acne
The progesterone in the contraceptive injection can cause acne or make existing acne worse.
Decreased sex drive
Hormonal contraception can also impact your libido. No research has currently found a link between progestogen-only contraception (such as the injection) and changes to sex drive. However it may indirectly do so, by causing other side effects as listed here.
Mood swings
Depression is listed as a side effect of the contraceptive injection however like libido, it’s difficult to establish whether or not this is directly linked. Various studies show users of Depo-Provera experienced mood swings during use, whilst others show no changes. Women with a history of mental health disorders should always speak to a doctor before using hormonal contraception.
Headaches
All hormonal methods of contraception can cause headaches, particularly as your body gets used to the new method. Those who have migraines sometimes note better or worse symptoms.
Hair loss
The contraceptive injection has the potential to cause hair loss or thinning. This is usually temporary and the hair starts to regrow once you come off the injection.
These are similar to the side effects of the mini pill. However unlike the pill, you can’t stop taking the injection - once it’s been administered, the hormones will stay in your body for 8-13 weeks. Find out more about concerns whilst using the pill.
The main disadvantage of the contraceptive injection is that it may delay your return to fertility. After stopping the injection, it can take up to a year before your menstrual cycle returns to normal and you begin ovulating again.
The contraceptive injection also presents a small number of risks. Very rarely, some people may have an allergic reaction or infection at the site of the injection.
The Depo-Provera injection can also cause thinning of the bones therefore it is suggested to stop using this method after two years.
There are no reported higher risks of blood clots whilst using the contraceptive injection.
Where to get the contraceptive injection
You can get the contraceptive injection from your local GP surgery, contraception clinic or STI clinic for free - even if you’re under 16.
In summary, the contraceptive injection is a hormonal method of birth control that provides 99% effectiveness against pregnancy for two to three months. It’s a very reliable and convenient method for people who worry about forgetting the pill or who don't like the idea of a coil.
Find out more about the different types of contraception, including other long-term hormonal methods.
References
https://www.nhs.uk/conditions/contraception/contraceptive-injection/
https://womensmentalhealth.org/posts/does-depo-provera-cause-mood-changes/
https://pubmed.ncbi.nlm.nih.gov/29979329/
https://www.fsrh.org/documents/fsrh-ceu-statement-contraception-and-weight-gain-august-2019/
