It is made from naturally occurring plant steroids found in the wild yam, and various other natural sources. It is NOT the synthetic version that is commonly purchased as tablets with a prescription such as Provera. The synthetic progesterone can produce severe side effects including increased risk of cancer, abnormal menstrual flow, fluid retention, nausea, and depression. Side effects are extremely rare with natural progesterone. The only one of concern is that it might slightly alter the timing of the menstrual cycle.
Natural progesterone is very useful to balance excess estrogen.
Natural progesterone is also different from estrogen in that your body can use it as a precursor or starting material to make other hormones such as adrenal hormones. It can even convert it into estrogen or testosterone if your body needs it. The following table lists the properties of estrogen relative to progesterone. Ovarian cysts or tumors can lead to excess estrogen production. Stress also increases production, but probably the most common cause is obesity.