Contraceptive injections

Contraceptive injections contain a depot ? or store ? of a synthetic, progesterone-like hormone, called a progestogen. After injection into a muscle ? usually in the buttock ? the hormone is released very slowly into your body to prevent pregnancy.

There are two types of contraceptive injection. Depo-Provera is the most commonly used contraceptive injection, and contains a progestogen called medroxyprogesterone acetate. It protects you against pregnancy for 12 weeks. The other injection, Noristerat, contains a progestogen called norethisterone enantate and gives contraceptive protection for 8 weeks.

How effective is a contraceptive injection?
It is over 99% effective.

How do contraceptive injections work?

• They stop your ovaries releasing an egg each month (ovulation).
• They thicken the mucus from your cervix, making it difficult for sperm to swim through it and reach an egg.
• They make the lining of your womb thinner so it is less likely to accept a fertilised egg.

  What are the advantages of contraceptive injections?
  

  • You don't have to think about contraception for as long as the injection lasts.
  • They do not interfere with sex.
  • You can use them if you are breastfeeding, although the first dose is then delayed until 6 weeks after birth.
  • They give you some protection against cancer of the womb.
  • They give some protection against pelvic inflammatory disease.
  • They are useful if you cannot take oestrogens, like those in the combined oral contraceptive pill.

  What are the disadvantages of contraceptive injections?
  

  • Your periods will probably change. At first, bleeding can be irregular and may last for longer than usual. Or your periods may stop altogether. A few women have frequent light bleeding. This may be a nuisance but is not harmful.
  • Irregular bleeding may continue for some months after you stop the injections. See your doctor if you are worried.
  • Some women put on weight when they use Depo-Provera.
  • Other possible side-effects include headaches, acne, tender breasts, mood swings and bloating.
  • The injection works for 8 or 12 weeks, depending on which type you have. It cannot be removed from your body, so if you do suffer from any side-effects, they may continue during this time and for some time afterwards.
  • Your periods, and fertility, can return immediately. However, after stopping the Depo-Provera injections, they may take a few months to return. Sometimes it can take more than a year for your periods and fertility to get back to normal.
  • Long-term use of Depo-Provera lowers oestrogen levels, and may increase osteoporosis. (This is bone loss, which some women suffer from after the menopause.) The Committee on Safety of Medicines in the UK therefore recommend that women with risk factors of osteoporosis use a different method of contraception. After using the contraceptive injection for 2 years, it is also a good idea to have your osteoporosis risk factors re-assessed. Taking oestrogen together with the injection may offer some protection.

  Contraceptive injections do not protect you against sexually transmitted infections, so you may have to use condoms as well.

  For further information contact the fpa

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