The Contraceptive Injection

The most common injection used in the UK is intramuscular medroxyprogesterone acetate (otherwise known as Depo-Provera). The contraceptive injection works just like a mini pill. It contains a progesterone (a type of sex hormone) which:

• thickens the mucus at the entrance to the womb (so sperm can’t get in)
• prevents ovulation (the release of an egg)
• makes it more difficult for a fertilised egg to implant by changing the lining of the womb

That it works in three ways means that even if one of these mechanisms should fail, you are still protected from pregnancy. In fact, the contraceptive injection is over 99% effective if injections are on time, which means that less than one in 100 women who use it get pregnant within a year. Sometimes it can be difficult to remember to have the injection on time so the overall effectiveness of the injection at preventing pregnancy is actually around 94%. The contraceptive pill is just as effective if used correctly but its effectiveness is diminished if you forget a tablet. With the Depo-Provera injection, all you have to remember is the regular visit to your GP, every 12 weeks.

The two most common contraceptive injections in the UK are called Depo Provera and Noristerat. Most women who use the injection are on Depo Provera.

Depo Provera

Depo Provera is a contraceptive injection which prevents pregnancy for 12 - 14 weeks. You have to have your repeat injection after 12 weeks and it’s important that you get it on time. You should have the first injection within the first 5 of your period. This way, you will be protected immediately. Otherwise you would need to use condoms for the first 7 days after your injection. Sayana Press is another injection which contains the same hormone as Depo Provera but is given under the skin rather than into the muscle.

Noristerat

Noristerat contains a different progesterone than Depo Provera. It is not as commonly prescribed because it only protects you for 8 weeks, after which the injection has to be repeated.

Like all hormonal contraceptives, the injection can cause side effects.

Possible side effects of the contraceptive injection:

• headache
• abdominal pain
• weight gain
• nausea or bloating
• dizziness
• acne and other skin problems
• fluid retention
• weakness
• irregular bleeding or spotting
• vaginal discharge
• breast tenderness or pain
• changes affecting your mood and sex drive
• thinning of the bones

In addition, once you stop taking the contraceptive injection, it may take up to a year for your periods and fertility to return to normal.

For all possible side effects of the contraceptive injection, read the patient leaflets for Depo Provera, Sayana Press or Noristerat.

The injection is not suitable for everyone and your doctor will have a consultation with you to determine whether you can use it or not. It is not suitable if you:

• are pregnant
• have or have had breast cancer
• suffer from vaginal bleeding between periods
• have problems with your arteries (including if you have had a heart attack or stroke)
• have or have had liver cancer or severe liver disease
• are allergic to any of the ingredients

It may not be suitable for you if you suffer with certain other medical conditions so you should always chat to your doctor before starting this.

Does the contraceptive injection cause weight gain?

In some women, the contraceptive injection causes weight gain. Clinical trials for Depo Provera showed, that the average weight gain over 1–2 years of using the injection was 5–8lbs. Women who used the injection over 4–6 years gained 14–16.5lbs on average. This side effect does not affect all women.

What are the advantages?

The biggest advantage of the contraceptive injection is convenience – all you need to do is get the injection every 12 weeks. This makes the jab a very safe and reliable contraceptive. Although it is only as effective as the pill on paper, in reality it tends to be safer as some women forget to take the pill on time now and then. It can also cause lighter or less frequent periods and may offer some protection against cancer of the uterus and ovaries.

It is possible to use the contraceptive injection during breastfeeding.

What are the disadvantages?

Although it is very convenient, the injection also has disadvantages:

• You can’t change your mind - Once you have been given the injection, the active ingredient will be in your body for two to three months. You will not be able to get pregnant in that time and if you suffer side effects, they may persist until the 8 or 12 weeks are over
• You have to visit your GP every time your injection is due
• You should not have it if you want to have a baby in the coming year as you might not ovulate for a while after you have stopped having injections

There is also a possible weak link between developing breast or cervical cancer and using the injection, though this risk is likely to reduce after stopping the injection.

Depo-Provera (2020) EMC [last accessed 31 March 2020]

Noristerat (2019) EMC [last accessed 31 March 2020]

Progesterone-only injectable (2019) FSRH [last accessed 31 March 2020]

Sayana Press (2019) EMC [last accessed 31 March 2020]