All of the statements regarding progesterone only pill are true, except: (A) Inhibits ovulation, (B) Failure rate is the same as combined OCP, (C) Irregular bleeding is a known complication, (D) Acts by altering the cervical mucous
Answer is B. 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.