Because the mini pill contains no estrogen, a woman theoretically has a lower risk of blood clot formation and heart attacks compared to a woman taking the combined oral contraceptive pill. There are no studies, however, to document this. Overall, the mini pill is less effective than the combined oral contraceptives in protecting against pregnancy. Many women experience some change in their bleeding pattern when taking the mini pill. This is most common when a woman has been on the mini pill for longer than six months.
Some women experience minor headaches, nausea, weight gain, depression, and cramping.
Some studies have demonstrated that taking progesterone alone may cause an increase in cholesterol. Ovarian cysts are more common among mini pill users. The cysts usually disappear without treatment and rarely cause problems. Have a back-up birth control method such as condoms with spermicide or a diaphragm available. You will need to use your back-up method for the first month.