Progesterone may be prescribed if a woman has a normal menstrual cycle and then stops having periods. During pregnancy, particularly during the first trimester, Progesterone supplements can help maintain the pregnancy. Progesterone is also prescribed in post-menopausal women during hormone replacement therapy.

Progesterone can cause several Side Effects. Headache, breast tenderness, diarrhea, vaginal discharge, and problems with urination are some Side Effects that tend to be transient. If these persist, a woman taking Progesterone supplements should tell her doctor. Some people taking Progesterone may experience dizziness or drowsiness. Progesterone should therefore not be taken before driving or operating heavy machinery. Other Side Effects may be more serious, and if they occur, a woman taking Progesterone should contact her doctor immediately. Because Progesterone causes increased blood clotting, it can contribute to a heart attack, blood clots in the lungs and legs, or even stroke. Some signs of such serious Side Effects are chest pain, blurred vision or loss of vision, numbness or tingling in the arms or legs, and sudden shortness of breath. Other serious Side Effects that warrant immediate medical attention are unexpected vaginal bleeding, breast lumps, migraines, and uncontrollable shaking.

Some brands of Progesterone capsules, such as Prometrium, contain peanut oil and may trigger a life-threatening allergic reaction in people who are allergic to peanuts. Women over the age of 65 who take Progesterone as part of hormone replacement therapy are at increased risk of developing dementia. Women who suffer from depression may also experience a worsening of their depression while taking Progesterone supplements. Synthetic Progesterone compounds or progestogens decrease good HDL cholesterol, may increase blood pressure, contribute to mood disorders, and may exert effects of male hormones such as increasing facial hair growth. Women taking synthetic Progesterone should switch to natural Progesterone, which does not exert these Side Effects.