All of the statements regarding progesterone only pill are true, except
Failure rate of combined OCP is 0.2/100 women years, whereas failure rate of progesterone only pill is about 0.5 - 2 per 100 women years of use. Progesterone only pill acts by thickening cervical mucous, causing atrophy of endometrium or by inhibiting ovulation.
Inhibits ovulation
Failure rate is the same as combined OCP
Irregular bleeding is a known complication
Acts by altering the cervical mucous