Who can use contraceptive injections?
Contraceptive injections use the hormone progesterone to prevent pregnancy for about 12 weeks at a time
The injections are more than 99% effective when used correctly and trick your body into thinking you’re already pregnant
You need a healthcare professional to give you the injection and you need to remember to get it renewed to stay protected
Extra advantages of the contraceptive injection include not having to remember contraception on a daily basis
The contraceptive injection can cause some side effects like irregular bleeding, headaches, weight gain, mood changes, stomach issues, acne, and breast tenderness
The information in this article relates to the most commonly used contraceptive injection in the UK, which is called intramuscular medroxyprogesterone acetate (otherwise known as Depo-Provera).
This contraceptive method involves an injection of the hormone progesterone, which prevents pregnancy for about three months (12 weeks). Contraceptive injections are more than 99% effective when used correctly. The injection needs to be renewed on time every 12 weeks.
When artificially produced progesterone is given as an injection, it suppresses ovulation by tricking your body into thinking that you are already pregnant.
Contraceptive injections do not protect against sexually transmitted infections (STIs).
How do progesterone injections work?
Progesterone injections are usually given in the bottom (sometimes the leg or the arm), during the first five days of the menstrual cycle. This way, you are immediately protected. If given outside of this window condoms are required for an additional 7 days. Only healthcare professionals can give you a contraceptive injection, so you need to visit your GP or a sexual health clinic if you’re interested in using this method of contraception.
Progesterone works by stopping your ovaries from releasing an egg each month (ovulation), and by thickening the tissues in your cervix (neck of the womb) so that sperm can not get to the fallopian tubes, which lead to the ovaries.
Once injected into a muscle, progesterone is gradually released into the body, providing three months protection against pregnancy.
The hormone also thins the lining of your uterus, making it more difficult for a fertilised egg to implant.
The follow up injection can be given up to 14 days before the end of the three months (between weeks 10 and 12).
Although the manufacturer advises that the injection should be given every 12 weeks, in practice this is usually given every 13 weeks. If it’s given after 14 weeks, additional contraceptive protection will be required (and emergency contraception if you have unprotected sex).
How effective are progesterone injections?
In ideal use (meaning the injection is renewed on time), the protection is above 99% effective over a period of 1 year. UK statistics show that due to the way the injections are actually used (women sometimes forgetting to have the injection renewed on time) the effectiveness is 94%. This makes the injection more effective than the contraceptive pill and condoms, but less effective than intrauterine contraceptive devices and the progesterone-only implant.
Advantages of contraceptive injections
The contraceptive injection is often suitable for women who cannot take the combined pill, patch, or vaginal ring. The injection itself is safe and allows you to forget about contraception when having sex – at least for three months.
It provides the same benefits as other hormonal contraceptives such as less painful and lighter periods (sometimes none at all) and may offer some protection against cancer of the uterus and ovaries.
Other advantages of the progesterone injections include:
- Women who are breastfeeding can use it
- Very few interactions with other drugs, including antibiotics
- Women over 35 can use it
- It can help with symptoms of endometriosis and is safe to use in patients with sickle cell anaemia
Like progesterone cream, progesterone injections are not recommended for treating menopause.
Progesterone injection side effects
Even though the progesterone injection only provides reliable protection for three months, its effects on fertility may last up to a year in some women.
Very common progesterone injection side effects (affecting more than 1 in 10 women) include:
- abdominal discomfort
- weight gain
Common progesterone injection side effects (affecting between 1 in 100 and 1 in 10 women) include:
- mood swings or low mood
- nausea or bloating
- acne and other skin conditions including alopecia
- fluid retention
- muscle pains
- vaginal discharge
- breast pain
- painful periods (the injection can also be used as a treatment for this)
- vaginal or bladder infection
For less common side effects, discuss with your nurse or doctor or request the patient information leaflet that comes with your injection. Always talk to your doctor about any medications that you’re taking, including over the counter and herbal remedies, to make sure these don’t affect the injection.
While a progesterone injection tends to reduce bleeding and pain in periods, some women may get the opposite symptoms. Some women stop using contraceptive injections because of this. But, you should discuss this with your doctor first as treatments are available to help with these symptoms .
Sayana Press, the subcutaneous version of the progesterone only injection, has a higher risk of injection site infections than Depo-Provera.
Using the injectable contraceptive can cause thinning of the bones. This is mostly a problem for women at risk of or suffering from osteoporosis. Bone density usually returns to normal once women stop using the injections.
Because they affect bone density, progesterone injections are not routinely recommended for women under 18, since their bodies are still growing and an alternative method of contraception should be considered in women over the age of 50.
There is a possible weak connection between using the progesterone-only injection and developing breast cancer and cervical cancer. But any risk is likely to reduce with time after stopping.
Precautions on use
The progesterone injection is not suitable for you if:
- you’re pregnant
- you’ve had or have breast cancer
- you suffer from vaginal bleeding between periods
- you have had a heart attack or stroke or suffer from ischaemic heart disease or vascular disease
- you’ve had or have liver cancer or severe liver disease
- you’re allergic to any of the ingredients
It may not be suitable for you and you should first discuss with a doctor if:
- you suffer from high blood pressure, diabetes, high cholesterol or obesity
- you‘ve just given birth (it's usually preferable to wait 6 weeks)
- you’re a smoker
- you’ve had or have benign liver tumours
- you’re underweight
- you drink alcohol excessively
- you have a personal or family history of osteoporosis
- you are currently suffering from blood clots
- you are taking certain medications long-term such as steroids
- you suffer from severe depression
If you take ellaOne whilst using the injection condoms will be required for at least 14 days after this.
When in doubt, consult your doctor or local health provider to discuss your contraceptive options.
Contraceptive pills are a reliable way of reducing your risk of getting pregnant from sex. Zava offers most common brands of pill, so you can order your preferred brand by visiting our contraceptive pill service page.
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