From wikipedia: Progesterone also known as P4(pregn-4-ene-3,20-dione) is a C-21 steroid hormone involved in the female menstrual cycle, pregnancy (supports gestation) and embryogenesis of humans and other species. Progesterone belongs to a class of hormones called progestogens, and is the major naturally occurring human progestogen.

Progesterone is commonly manufactured from the yam family, Dioscorea. Dioscorea produces large amounts of a steroid called diosgenin, which can be converted into progesterone in the laboratory.