The contraceptive injection is given once every 13 weeks in a muscular area, usually the buttocks. There is another injectable method which can be given by yourself once you have been observed doing this and are happy to do so.
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How effective is the contraceptive injection?
The contraceptive injection is more than 99% effective. That means that if the injection is taken on time, fewer than 1 in 100 users will get pregnant.
Furthermore, because the injection is a form of long-acting reversible contraception (LARC), there is no room for user error.
How does the contraceptive injection work?
The contraceptive injection works by releasing the hormone progestogen. This helps to do the following things:
- Prevent the release of an egg every month
- Thickens the lining of your uterus so it’s less likely to accept an egg
- Thickens the mucus in your cervix which makes it difficult for sperm to move through it and reach the egg
How does the contraceptive injection affect other parts of my health?
Whilst you may still bleed whilst on the contraceptive injection, they are not technically periods as the injection prevents ovulation. Furthermore, your periods may be less heavy/painful and you may experience less discomfort pre-menstruation.
This bleeding may change in a way which is not acceptable. This irregular bleeding may last for some months even after you stop using the injection. In some patients, it can take upto one year before your periods return to normal.
If you are experiencing bleeding after sex and/or vaginal discharge/pain, please seek advice from your clinician for further investigation.
There is evidence to suggest that you will put on 3kg over the course of using the injection. Whilst this might not be a problem for some women, it very much may be for others.
It can take upto one year before your periods and fertility return to normal, after you stop using the injection.
The contraceptive injection affects your natural estrogen level and may decrease your bone density. For most people, this isn’t a problem as the bone replaces itself once you stop using the injection and research does not show any long term problems.
However, if you are at risk of Osteoporosis (thinning of the bones) it’s normally advisable to use another method of contraception. Factors increase risk of Osteoporosis include:
- Lack of estrogen due to menopause or early menopause (before 45 years)
- A lack of estrogen due to missing periods for 6 months or more, as a result of over-exercising, extreme dieting or eating disorders
- Lifestyle factors (e.g. smoking, heavy drinking, long term use of steroids)
- A close family history of osteoporosis
- A certain medical condition affecting the liver, thyroid and digestive system
- Being underweight
A bone scan is not usually recommended before starting the contraception injection, but may be useful in those at risk of developing Osteoporosis.
Furthermore, you can ensure healthier bones by:
- Doing regular weight-bearing exercises (e.g. running & walking)
- Eating a diet rich with calcium and Vitamin
- Reducing alcohol and smoking
You can continue to breastfeed as normal whilst on the contraceptive injection.
You can continue using most medications whilst on the contraceptive injection. This will be discussed with you before administering your contraceptive injection.
Some people experience side effects such as spotty skin, hair loss, decreased libido, mood swings, headaches, breast tenderness and abdominal bloating.
It’s a good method if estrogen-based methods don’t suit you (such as the combined pill, path and vaginal ring).
Can anyone use a contraceptive injection?
The contraceptive injection is available to most women. However, the injection may not be recommended to individuals who:
- Want a baby within the next year
- Want to have a regular period
- Have breast cancer (or have had it in the past)
- Have arterial disease or history of heart disease or stroke (or have had it in the past)
- Have unexplained bleeding from the vagina (e.g. between periods and after sex)
- Have serious disease of the liver (or have had it in the past)
- Are at risk of Osteoporosis (thinning of the bones)
Are there any additional risks I should be aware of?
- As with any injection, there’s a small risk of a reaction at the spot the injection is given, which may cause irritation, swelling or a scar.
- Research surrounding the increased risk of breast cancer and hormonal contraception is complex and sometimes contradictory.
We will discuss all the risks with you before providing any method of contraception.
Page reviewed by Julie Milsom (Specialist Nurse in Sexual Health)
Last reviewed date: 27 April 2021
Next review due: 27 April 2024
Whilst this content is written and reviewed by sexual health specialists, it is for general guidance only. It is not intended to replace the advice of your clinician.
References & Further Reading
- Contraception: A prospective study of immediate initiation of depo medroxyprogesterone acetate contraceptive injection
- Journal of Pediatric and Adolescent Gynecology: Adolescent Use of the Monthly Contraceptive Injection
- Contraception: Bleeding patterns of adolescents using a combination contraceptive injection for 1 year
- American Family Physician: New Contraceptive Options – American Family Physician
- Contraception: Depot-medroxyprogesterone acetate injection (Depo-Provera®): a highly effective contraceptive option with proven long-term safety
- FPA: Contraceptive Injections