Your health & the injection
All methods of contraception have:
- health benefits which are factors that could improve your health
- side effects which are symptoms that do not affect your health but can affect the quality of your life in either a positive or negative way
- health risks which are factors that could have an important negative impact on your health
Health benefits
The injection may provide some protection against cancer of the womb and pelvic inflammatory disease.
For people with sickle cell disease, the injection may help to lower the severity of sickle cell crisis pain.
Side effects
Periods and bleeding
The contraceptive injection changes the pattern of your bleeding. Your periods may stop or you might have irregular bleeding. This is when your bleeding does not happen at the same time each month.
We might recommend the contraceptive injection for people who have problems with their periods, because it can cause them to stop. For example,
- premenstrual syndrome
- heavy periods
- painful periods
- endometriosis
Although some people have no bleeding from the start, irregular bleeding is very common in the first 6 months and then gradually settles. This is not dangerous in any way.
- After 3 months of taking the injectable contraceptive 10% of women have no bleeding.
- After 12 months of taking the injectable contraceptive 50% of women have no bleeding.
- One in a hundred people have ongoing problems with irregular bleeding on the injectable contraception, so not everyone stops their period.
Depending on how it affects you, the change in bleeding pattern may be an advantage or a disadvantage. If you have a lot of irregular bleeding, it can be very inconvenient. If you have very light irregular bleeding, it may not bother you.
If you are struggling with irregular bleeding, your GP may prescribe the combined pill on a temporary basis. The combined pill contains oestrogen, which may stimulate a period and help to regulate your cycle.
Bleed vs Period
We use period to describe the bleeding that happens during a menstrual cycle. In the first half of your cycle, when you produce oestrogen, the lining of your womb builds up. In the second half of your cycle, if you have not become pregnant, the lining is released and comes out of your body as a period. This process repeats itself approximately every 28 days.
We use bleeding or a bleed to describe the bleeding that happens when you are using a contraceptive method that changes your menstrual cycle. When you take a progestogen-only method the lining of your womb stays the same throughout the cycle. Progestogen doesn’t always maintain the lining in the same way which is why some people experience bleeding. We do not know why some people experience irregular bleeding more than others.
We use spotting to describe the amount of blood. Spotting is a smaller amount of blood that is less than a period or a bleed.
Weight gain
Some people experience weight gain when using the contraceptive injection. We think this is because it can increase appetite, so you may feel hungrier than usual.
Weight gain is more common if you are:
- under the age of 18
- have a body mass index of over 30kg/m2
If you gain more than 5% of your body weight in the first 6 months of using the contraceptive injection, then you are likely to continue to gain weight.
For example,
- If you weigh 57kg or 9 stone, 5% of your body weight would be 3kg or 6 pounds. This is just under half a stone.
- If you weigh 70kg or 11 stone, 5% of your body weight would be 4kg or 8 pounds. This is just over half a stone.
Unproven side effects of the injection
Hair loss
There is no conclusive evidence to associate injectable contraceptives with hair loss. However, at least one large study has reported this side effect in up to 10% of women.
Headache
Headaches are common in the general population so it is difficult to show a causative effect. Some studies have shown that up to 15% of women experience headaches on the injectable contraceptive.
Other symptoms
Acne, mood swings and a decreased interest in sex have all been reported in users of injectable contraceptives but there is no proven link.
Health risks
Mental health
We do not know, for certain, what the relationship is between the contraceptive injection and low mood or depression. The evidence on this is conflicting with some studies showing an increased level of depression among users of injectable contraceptives and other studies showing no increased risk.
Bone density and Osteoporosis risk
Oestrogen plays a role in maintaining bone strength. It is usually produced during the first half of the menstrual cycle. The contraceptive injection stops ovulation which also stops the menstrual cycle. This means less oestrogen is produced. Lower levels of circulating oestrogen in the body are linked to a small loss in bone mineral density.
Bone density usually returns to normal when you stop using the contraceptive injection.
This is more important for some age groups:
- Women who are under the age of 18 may not have reached their adult bone mineral density yet.
- Women who are over the age of 45 years need to have maximum bone strength as they will lose bone mineral density after the menopause.
We have reviewed the current research. From the scientific evidence, it is not clear if the loss of bone density results in an increased risk of fractures e.g. a broken bone.
Other things that might cause lower bone mineral density include:
Things that might cause a higher bone mineral density include:
- weight bearing exercise e.g. running
- a healthy diet
Every 2 years, we have a discussion with all our contraceptive injection users to assess their risk of osteoporosis. Your GP or Sexual Health Clinic should do the same.
Breast cancer
There may be a small link between the injectable contraception and breast cancer. Any increased risk is likely to be very small and would reduce when you stop the injectable contraception.
Unproven risks
There has been extensive research to understand if the contraceptive injection increases the risk of getting HIV. To date, there is no conclusive evidence that the injectable contraceptives increase risk of HIV.
