Hello, Welcome to HCM, I have read your query, and duphaston tablets contain dydrogesterone, a synthetic derivative of the female sex hormone progesterone, which means that its chemical structure closely resembles that of naturally produced progesterone and it therefore works in a similar way. Endogenous (naturally produced) progesterone is produced by the ovaries during the second phase of the menstrual cycle. It acts on the endometrium (lining of the uterus) converting the proliferating phase to the secretory phase. This causes the endometrium, which has thickened in response to oestrogen during the first half of the cycle, to stop growing and start secreting hormones and other proteins needed to maintain a pregnancy, if conception occurs; if not, levels of oestrogen and progesterone fall and the endometrium is shed (menstruation). The action of dydrogesterone in Duphaston helps re-establish a regular menstrual cycle in conditions where a lack of endogenous progesterone causes menstrual problems, and helps in the treatment of infertility and spontaneous abortion (miscarriage) by stimulating the endometrium to prepare for a pregnancy and protect an existing pregnancy. Duphaston tablets 10mg act on the endometrium in all its locations to stop it growing, which alleviates symptoms of endometriosis including pain and bleeding. Susten (progesterone) is also used for protecting the lining of the uterus in certain women who are also taking estrogen. It is used to treat certain women who have do not have a menstrual period because of decreased progesterone in the body. The most frequently reported side effects when taking these tablets include: nausea, bloating, breast pain, irregular bleeding, dizziness, weight gain, skin rash and itch. If these side effects continue and are not tolerable then will recommend you to visit your gynaecologist. Thanks