Hello, Thank you so much for your question. Progesterone pill for micronized progesterone is natural oral progesterone that the same structurally identical to the progesterone secreted by the ovary. it is prescribe frequently now, it protects the endometrium, and has little impact upon serum lipids. We suggest micronized progesterone as first line progestin because it is effective for endometrial hyperplasia, is metabolically neutral, and does not appear to increase the risk of either breast cancer. Progesterone helps to regulate your cycle. After you ovulate each month , progesterone helps thicken the lining of the uterus to prepare for a fertilized egg. Side effect of progesterone including nausea, breast tenderness, bloating and mood changes -these typically improve within two to three months without treatment. Bleeding between periods-irregular bleeding, also called breakthrough bleeding or spotting, is particularly common during the first months of taking the pill. It almost always resolves without any treatment within two to three months. Forgetting a pill can also cause breakthrough bleeding. Hope I have answered your query. Let you know if I can assist you further. Best regards, Dr. Heang Chan Raksmey, General and Family Physician.