Progesterone - is an endogenous (produced in the body) steroid and progestogen sex hormone involved in the menstrual cycle , pregnancy , and embryogenesis of humans and other species. Progesterone has a variety of important functions in the body. It is also a crucial metabolic intermediate in the production of other endogenous steroids , including the sex hormones and the corticosteroids , and plays an important role in brain function as a neurosteroid . Progesterone