How effective is the progesterone-only pill?
Very effective, when it’s used correctly. There are two methods used to measure effectiveness: perfect use and typical use.
Perfect use is taking the mini pill exactly as stated in the instructions, without making any mistakes. Effectiveness associated with this method is over 99%, meaning that in 100 women taking the pill over a year, less than one will get pregnant.
Typical use is taking the pill correctly for the most part, but making occasional mistakes (missing a pill, or taking it late). Effectiveness for this method is thought to be around 91%, meaning that around nine in 100 women using the progestin only pill will get pregnant over one year.
When to start taking the progesterone-only pill
If you’re not already taking the pill or using another form of hormonal contraception, you can start taking the progesterone-only pill at any point during your cycle. Or you can wait until you have your period.
When you’re ready to start using progesterone-only birth control, pick a convenient time to take it because you’ll have to take it at this time every day.
If you wait for your period, and you start taking the mini pill within the first five days of your period, you’ll be protected from becoming pregnant right away. So you don’t need to worry about using a diaphragm or condoms.
You might need to go with another method of birth control if you have a shorter period. Use condoms or the diaphragm or avoid sex until you’ve used the pill for two days.
You won’t be protected against pregnancy right away if you start taking it at any other point during your cycle. So if you’re not on your period and start taking the progesterone-only pill, make sure you use extra protection like a condom for the first seven days that you take it.
Starting when switching from another pill
When you switch from the combined pill or another type of progesterone-only pill, you can take your first one the day after you finish the last pill in your previous pack.
If you’re changing from the skin patch or the vaginal ring, start on the day after your patch or ring is removed. If you do this, you won’t need to use extra protection.