Progesterone Pill

Would a natural progesterone pill or the natural progesterone creams for that matter, protect you against getting pregnant?

There are no natural progesterone containing birth control pills that I know of at the present time. Historically when researchers first developed oral contraceptives, they were looking for a way to manufacture progesterone from Mexican yams and when they first discovered the contraceptive effects of their manufactured progestins, they were very excited. As they purified the compounds to contain only progestins and not the contaminant estrogen (specifically mestranol) they lost the contraceptive effect of the pills. Thus the discovery that you needed both progestin and estrogen to have an effective contraceptive pill by mouth.

Now we know that progestin only pills can function as contraceptives, not by inhibiting ovulation but by making the cervical mucous hostile to sperm penetration and the endometrium hostile to fertilized egg implantation. But they are not as effective as combined oral contraceptives in preventing pregnancy. The typical use failure rate of progestin only pills is about 5%.