Over-the-counter progesterone cream can expose you to as much as oral prescription progesterone pills:

Women who use over-the-counter progesterone creams could be Exposed to hormone levels comparable to those used in a form of hormone replacement therapy, a small study suggests.

The study compared one brand of progesterone cream with a prescription oral progesterone that, like the cream, is derived from plant sources and provides a hormone that is structurally identical to the natural progesterone in a woman's body. The prescription product, Prometrium, is used as part of hormone replacement therapy (HRT) after menopause, and for restoring menstruation in younger women whose periods have stopped because of another illness.

The study found that the over-the-counter cream, when taken as the label directs, exposed study volunteers to as much hormone as the prescription did.

("Progesterone cream may deliver high hormone dose", Reuters, Jul.27)