Contraceptive injection

How effective is it?

Over 99 per cent effective.  Less than four woman in 1000 will get pregnant over two years.

How does it work?

Releases the hormone progestogen which stops ovulation, thickens cervical mucus to prevent sperm reaching an egg, and thins the lining of the uterus to prevent a fertilised egg implanting.

What are the advantages?

  • Depo provera lasts for 12 weeks.
  • You do not have to think about contraception for as long as the injection lasts.
  • May alter periods: make periods stop, become lighter or less frequent.


What are the disadvantages?

  • May alter periods: can become irregular or longer than usual.
  • Periods and fertility may take time to return after stopping the injection.
  • Some women gain weight.

Anything else I should know?

  • The injection cannot be removed from the body so any side-effects may continue for as long as it works and for some time afterwards.
  • Not affected by other medicines diarrhoea or vomiting.