Hello and welcome to HCM Duphaston is a progesterone preparation. Progestreone is a naturally occuring female hormone. Its role is to produce secretory change in the endometrium. During the first half of the cycle there is proliferation of the endometrium and during the second half there is secretory change. Secretory change prepares the endometrium for implanatation. If pregnancy occurs then progesterone maintains the pregnancy for 12 weeks. After 12 weeks placenta takes over. So, progesterone maintains pregnancy. In the absence of progesterone pregnancy cannot be sustained and it results in pre-term labour, abortions etc. Progeserone is also indicated in other conditions like irregular menstrual cycle, other menstrual disorders, infertility etc. The role of progesterone is to regularize the cycle in case you have irregular cycles. PCOS is another issue. It is due to abnormality of ovulation where the ovum/ egg does not mature. Progesterone is not used for that purpose. Thanks and take care Dr Shailja P Wahal