Hi, Letrozole belongs to the group of medications known as aromatase inhibitors which can reduce the amount of estrogen and used to treat female infertility. It is also used in the treatment of early and advanced breast cancer. Side effects of Letrozole are fatigue, hot flashes, excessive sweating, increased blood cholesterol level, headache, dizziness, back pain, anxiety, nervousness, increased thirst, constipation, bone fractures, allergic reactions and occasionally weight gain etc. Though this medication has some side effects, it is safe and effective for long term use if it is taken as directed by your doctor. Progesterone is the natural female hormone that is used to restore normal menstrual periods in case of amenorrhea or complete cessation of menstrual cycles, treat abnormal and prolonged uterine bleeding due to hormonal imbalance as well as premenstrual syndrome (PMS). Side effects of Progesterone are nausea, vomiting, abdominal pain, bloating, indigestion, headache, sweating, dizziness, fatigue, unusual tiredness and weakness, dry mouth, breast tenderness and enlargement, vaginal discharge, changes in body weight, delayed wound healing, vaginal bleeding, allergic reactions etc. These side effects are mild and self limiting. So, this medication can be taken for long term according to your doctor s advice. Take care. Hope I have answered your question. Let me know if I can assist you further. Regards, Dr. Zubayer Alam, General And Family Physician