How does the progestin only pill work?


  • The progestin only pill thickens cervical mucus (this blocks the sperm from meeting an egg)
  • The progestin only pill also disrupts the menstrual cycle, including preventing the release of eggs from the ovaries (ovulation) in 97% (of desogestrel) and 60% (other progestin) of women. 49
  • If used consistently (taking a pill every day without forgetting at the same time) Progestin Only Pills are more than 99% effective at preventing pregnancy for all women.
  • With ‘typical use’ (when women miss a pill or take it at the wrong time occasionally during the month) it is still very effective for women who are breastfeeding.  There will be approximately 1 pregnancy in every 100 women using Progestin Only Pills over a year (1% failure rate). It is less effective for women who are not breastfeeding.   About 3-10 women in every 100 women using progestin only pills (with ‘typical use’) over a year will get pregnant. (3-10% failure rate).46
  • Data suggest that all progestin only pills are equally effective at preventing pregnancy.