Forms of Contraception – Contraceptive Injection

The contraceptive injection (medroxyprogesterone) contains a type of hormone called a ‘progestogen’ that is injected into the muscle (usually in the buttock, leg or arm), which stops women from ovulating (producing eggs), thickens the mucus in the cervix – making it difficult for sperms to get through. They make the lining of the womb thinner, so that if an egg (ovum) became fertilised, it would have difficulty attaching itself to the lining. Each injection lasts for 3 months before a repeat injection must be given. It is around 99 per cent effective. The injection can be given up to and including the 7th day of your period. If started at any other time, abstinence or additional contraception has to be used for seven days.

There is a very high chance (40 per cent) that periods will be disrupted in some way and the commoner side-effects are as follows:

  • heavy periods (menorrhagia)
  • prolonged periods
  • irregular menses or infrequent periods (oligomenorrhoea)
  • absent periods – though many women are very grateful for this effect
  • headache
  • tummy ache
  • weakness
  • dizziness
  • weight gain
  • delayed return of fertility after stopping the jab

Most women can have the contraception injection, but it may be unsuitable if:

  • already pregnant
  • Want a baby within the next year
  • Don’t want periods to change
  • Have thrombosis, heart or circulatory disease
  • Have active liver disease
  • Have breast cancer now or within the past five years
  • Have migraines with aura
  • Have diabetes with complications or have had diabetes for more than 20 years
  • Have risk factors for osteoporosis


  • Very effective
  • Doesn’t interrupt sex
  • Suitable for women that cannot use oestrogens or are breastfeeding
  • May reduce heavy painful periods and help with premenstrual symptoms for some women
  • May give some protection against cancer of the womb
  • May give some protection against pelvic inflammatory disease
  • Not affected by other medicines


  • periods may change in a way that is not acceptable or they may stop
  • Irregular bleeding may continue for some months after stopping the injection
  • may have weight gain
  • Some women report having headaches, acne, mood changes and breast tenderness
  • The injection lasts for 12 weeks, so if women have side-effects they will continue during this time and for some time afterwards
  • periods and normal fertility may take some time to return – more than a year for some women