Progesterone is a steroid hormone produced in the corpus luteum, placenta, testes, and adrenal cortex that plays several key roles in the menstrual cycle and pregnancy. It causes development of the uterine lining after ovulation, increases basal body temperature, and supports a successful pregnancy by decreasing the mother's immune response and triggering labor when levels drop. Low progesterone can cause issues like infertility, depression, and menstrual problems, while high levels may lead to headaches and moodiness. Progesterone therapy has been shown to help treat various conditions by its anti-inflammatory, blood thinning, and neuroprotective effects.