Unlike the combined pill, the mini-pill or progesterone-only pill contains only one type of hormone. The active ingredient in this oral contraceptive is progestin, a synthetic version of the natural female sex hormone progesterone. When taken correctly, the mini-pill is 99% effective in preventing pregnancy. It works because it stops ovulation, stops sperm reaching an egg and prevents a fertilized egg implanting in the womb.
The mini-pill was first created for women who were breastfeeding because estrogen affects the production of breast milk. It is now used more widely.
The mini-pill is recommended for women who are over 35 years of age and smoke. It is also used by women who can’t take estrogen because of conditions like high blood pressure, blood clots or obesity. The mini-pill comes with 28 tablets in a packet. There are no placebo tablets. All of the tablets contain the active ingredient. For the mini-pill to be effective, you must take a pill every day at roughly the same time (within a three-hour window). You don’t have a break between packets – when you finish one packet you start another the next day – so you don’t have to remember to stop taking the tablets to have your period. If you start taking the mini-pill within the first five days of a period, you will be immediately protected against pregnancy. If you start the mini-pill outside of this time, you’ll need to use another contraceptive (e.g. condoms) for two days.
The mini-pill often leads to lighter, less painful periods, but four out of ten women also experience irregular bleeding. Discuss this with your doctor if it happens.