How does it work?
The hormone is injected into a muscle, usually during the first five days of a period, and is released very slowly into the body. Further injections are needed every 12 weeks. Discuss with your doctor the best time to have your first injection.
The injection acts primarily by preventing the ovaries from releasing an egg (ovulation). Less often it works by thickening cervical mucus to prevent sperm from joining an egg or by altering the lining of the uterus, which may prevent implantation of a fertilized egg.
How effective is it?
The injection is a long-acting reversible method of contraception (LARC). All long-acting methods are very effective because while they are being used you do not have to remember to take or use contraception. Contraceptive injections are over 99% effective. This means less than one woman in every 100 women using the injection will get pregnant in a year.
How effective any contraceptive is depends on how old you are, how often you have sex and whether you follow the instructions.
Where do you get the injectable contraception?
This method of contraception can only be given by a doctor or nurse. It is available on the GMS (medical card scheme).
What are the advantages?
- Once you have a regular injection you are protected from pregnancy.
- It does not interfere with sex.
- Can be used whilst breastfeeding.
- It is not affected by other medications.
- It may reduce heavy, painful periods and help with premenstrual symptoms for some women.
- It may give you some protection against cancer of the womb.
- It gives some protection against pelvic inflammatory disease.
What are the disadvantages?
- Your periods may change in a way that is not acceptable to you.
- There could be a delay of up to one year in the return of fertility after stopping the use of injectable contraceptives.
- As the injection lasts 12 weeks, you can only reconsider using it when the next injection is due. In the meantime, it cannot be removed from your body.
- The injection must be administered by a doctor or nurse in a family planning clinic or at a surgery.
- It will not protect you from sexually transmitted infections (STIs).
- It may be associated with weight gain and other side effects such as acne, breast tenderness, bloating and change in mood.
Who is it suitable for?
Most women who want to can have a contraceptive injection. Your doctor or nurse will need to ask you about your own and your family’s medical history to make sure the injection is suitable. Do mention any illness or operations you have had. Some of the reasons you should not use the injection are:
- You think you might already be pregnant.
- You do not want your periods to change.
- You want a baby within the next year.
Some medical conditions may make the injectable contraceptive unsuitable for you. These include:
- Breast cancer.
- Unexplained vaginal bleeding (for example, bleeding between periods or after sex)
- Thrombosis (blood clots) in any vein.
- A heart attack or stroke (serious arterial disease).
- Diabetes with complications or diabetes for more than 20 years.
- Active liver disease.
- Risk factors for osteoporosis.
If you currently have or previously had any of these conditions, you should discuss this with your doctor.
Are there any risks?
- Research about the risk of breast cancer and hormonal contraception is complex and contradictory. Current research suggests that women who use hormonal contraception appear to have a small increase in risk of being diagnosed with breast cancer compared to women who don’t use hormonal contraception. Further research is ongoing.
- You can have an allergic reaction to the injection, but this is rare.
- As with any injection there is a risk of a small infection at the site of the injection.
- Prolonged Depo Provera use (more than 3-4 years) is associated with a small loss of bone mineral density which is largely recovered when you stop using the contraceptive.
Will my periods be affected?
The injection may alter your periods. Some women find they have fewer or no periods, especially after one or more injections. A few women experience frequent light bleeding which may be a nuisance. Lack of periods or irregular periods in relation to this method are not harmful to your health. However, frequent and/or heavy bleeds which might occur can, in a women with a poor diet (low iron content), lead to anaemia.
Will I gain weight?
Not all women put on weight with the injection and some women lose weight. Use of Depo-Provera may be associated with an increase in weight of up to 2–3 kg over 1 year.
Pregnancy and injectable contraception
The injection is a highly effective method of contraception and if you have had your injections on time, it is unlikely that you are pregnant. If you think that you might be pregnant then you can do a home pregnancy test or speak to your doctor or nurse as soon as possible. If you do get pregnant while you are using the injection, there is no evidence that it will harm the baby.
Use post childbirth
If you have just had a baby it is believed that delaying the injection for six weeks often makes irregular bleeding less likely. It does not affect your milk supply. A small amount of hormone enters the milk, but it is harmless for the baby.
Use after a miscarriage or abortion
The injection can be started immediately after an abortion or miscarriage if you were pregnant for less than 24 weeks. You will be protected against pregnancy immediately.