The contraceptive injection pros, cons and potential side-effects

Dr Juliet McGrattan (MBChB)
·7-min read
Photo credit: Westend61 - Getty Images
Photo credit: Westend61 - Getty Images

From Netdoctor

Contraceptive methods are designed to prevent unwanted pregnancy. If used correctly, the contraceptive injection is more than 99 per cent effective and you can have sex without the worry of getting pregnant.

The contraceptive injection is the third most popular method of contraception in England (the combined pill and progesterone-only pill take the top two spots). It is convenient and effective and it can be used by most women.

To help you make an informed decision about contraception, Dr Juliet McGrattan offers her expert advice on the pros and cons of the contraceptive injection:

What is the contraceptive injection?

The contraceptive injection is one of several LARCs (long-acting reversible contraceptives) that give you contraceptive cover without you having to remember to use them every day or when you have sex.

There are three brands of contraceptive injections available:

The contraceptive injection releases a synthetic form of the naturally occurring hormone progestogen slowly into your bloodstream over 12 weeks or 8 weeks (depending on which brand is used) to provide long-acting contraception.

How does the contraceptive injection work?

The progesterone in the contraceptive injection prevents pregnancy by stopping your ovaries from releasing an egg each month. Egg release (ovulation) is required for pregnancy to occur.

The contraceptive injection also has two other effects that decrease the chances of a pregnancy. It thickens the mucus at the entrance of the womb which makes it more difficult for sperm to move up into the womb, as well as thinning the lining of the womb, so a fertilised egg is less likely to implant.

❗The contraceptive injection gives protection for 8 or 12 weeks - there is no way of reversing the effects of the injection once it is given.

How is the contraceptive injection given?

The contraceptive injection is usually given into a muscle – this can be the buttock (most commonly) or the upper arm. The injection produces a reservoir of the progesterone hormone that is released continuously into the bloodstream.

One type of contraceptive injection called Sayana Press is usually given in the tummy or thigh. Rather than into the muscle it is injected just under the skin.

The injection is usually given during the first five days after the beginning of a period. This will provide immediate protection. If it is not given during the first five days of a period, you need to be certain that you aren't pregnant before it is given. You must not have sex or you must use additional contraception, such as condoms, for seven days in this situation.

How effective is the contraceptive injection?

The effectiveness of any contraceptive is dependent on your age, how sexually active you are and how well you follow the instructions on how to use the contraceptive.

With the contraceptive injection if always used perfectly as directed according to the instructions, it is over 99 per cent effective. This means that less than one woman using the injection in 100 will get pregnant in one year. Using the contraceptive injection perfectly means that you must make sure you have regular three-monthly appointment to make sure you are given the injection on time and contraceptive protection is continued.

If the contraceptive injection is not used according to instructions, for example if you forget to have the injection within the first five days of your period when it is next due, then the risk of pregnancy increases to six users in 100 getting pregnant in one year.

Is the contraceptive injection right for me?

Most women can have contraceptive injections, including breastfeeding mothers and women who can't take oestrogen-containing contraceptives.

Your doctor may need to weigh up the risks and benefits of using the contraceptive injection. The contraceptive injection may not be suitable for you if you experience any of the following:

  • Breast cancer

  • Arterial disease, such as a stroke, angina or heart attack

  • Severe liver disease

  • Increased risk of osteoporosis

  • Unexplained vaginal bleeding that has not been investigated by the doctor

  • You are planning to have a baby within the next year

Photo credit: SCIENCE PHOTO LIBRARY - Getty Images
Photo credit: SCIENCE PHOTO LIBRARY - Getty Images

Contraceptive injection advantages

The contraceptive injection is a simple, safe and affordable contraceptive method, with the following advantages:

✔️ The contraceptive injection is 99 per cent effective if used correctly.

✔️ The contraceptive injection is a good option if you can’t use oestrogen-based contraception.

✔️ The contraceptive injection is safe to use during breastfeeding.

✔️ The contraceptive injection can be given immediately after childbirth, miscarriage or termination of pregnancy.

✔️ The contraceptive injection may help with heavy, painful periods and premenstrual symptoms for some women.

✔️ Most women find their periods stop altogether after the contraceptive injection.

✔️ The contraceptive injection is a long acting contraceptive, so you don’t have to remember to take it daily, unlike the pill. The injection can last for 12 weeks (or 8 weeks for Noristerat brand).

Contraceptive injection disadvantages

Some contraceptive methods come with side-effects and some health risks, so speak to your GP or sexual health advisor if you're not sure which method suits you. The potential disadvantages of the contraceptive injection include the following:

✖️ The contraceptive injection won't protect you against sexually transmitted infections; you'll still need to use condoms for that.

✖️ Breakthrough bleeding, spotting, heavy bleeding and irregular periods can be a common side-effect of the contraceptive injection. These are more common in the first three months and generally reduce with time.

✖️ There is a tendency for women to put on weight when they use Depo-Provera or Sayana Press contraceptive injections.

✖️ Some women experience side-effects such as mood swings, headaches, decreased libido and breast tenderness and acne after having the contraceptive injection.

✖️ The contraceptive injection may not be suitable if you want to have a baby in the near future, as there can be a delay of up to one year before the return of your periods and fertility after stopping the injection.

Contraceptive injection side-effects

All hormonal contraceptives can potentially give you side-effects. How you are affected is a very individual thing. Many women will have no problems at all or the effects are minor and bearable in return for very effective contraception. Side-effects associated with the contraceptive injection can include the following:

  • Headaches.

  • Changes to your period such as irregular bleeding or spotting, heavy bleeding, or stopping of your periods.

  • Vaginal discharge.

  • Breast tenderness.

  • Fluid retention, bloating.

  • Feeling sick.

  • Acne.

  • Hair loss (alopecia).

  • Reduced sex drive.

  • Mood swings or feeling depressed.

  • Weight changes.

How often do I need to see the doctor?

Before you have your first contraceptive injection you will need to discuss the risks and benefits with a doctor or nurse to make sure it is the right choice for you. You will then need to return for your injection every 12 weeks (or 8 weeks for Noristerat).

Sayana Press is a relatively new contraceptive injection and may not be available in your area. If it is, then you may be taught how to inject it yourself at home so you won't need to attend for appointments every three months.

If all is going smoothly with your injections you should see your doctor every two years for a review. This is to make sure that the injections are still the best option for you.

Contraceptive injections and bone health

One particular thing the doctor will review before your first injection and every two years, is your risk of osteoporosis (thinning of the bones). Contraceptive injections are associated with a small loss in bone density. This usually reverses when the injection is stopped.

If you are under 18 your bones are still being formed. An alternative contraceptive may be a better choice for you.

Around the age of 50 women's bodies naturally start losing bone density so women are generally advised to switch to another method of contraception.

Other factors that can reduce your bone density include:

  • Smoking.

  • High alcohol intake.

  • Being underweight.

  • Having a close family member with osteoporosis.

  • Taking steroid medications for long periods of time.

  • Whether you had more than six months of missed periods (amenorrhoea) before you started the injection.

  • Other medical conditions such as rheumatoid arthritis, coeliac disease, inflammatory bowel disease.

The doctor will take all of this into account before prescribing the injection and at your two yearly review. They will discuss the risk and benefits with you to make sure the injection remains the best contraceptive choice for you.

Further help and support

For further advice and information on choosing the right contraceptive for you, try one of the following:

Last updated: 13-01-2021

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