Celvestrant PFS Injection is an estrogen blocker. It is used in the treatment of breast cancer in women who have gone through menopause. It works by adjusting the level of estrogen and slow down the growth of cancer cells. Celvestrant PFS Injection is given as an injection into the muscles under the supervision of a doctor. It should be taken as doctor your doctor's advice. The dose and how often you take it depends on what you are taking it for. Your doctor will decide how much you need to improve your symptoms. You should take this medicine for as long as it is prescribed for you. The most common side effects of this medicine include injection site reaction, headache, vomiting, allergic reaction, and nausea. If these bother you, or appear serious, let your doctor know. There may be ways of reducing or preventing them. Before taking this medicine, tell your doctor if you ever had kidney or liver disease or had bleeding disorder or had any blood clotting medicine. Your doctor should also know about all other medicines you are taking as many of these may make this medicine less effective or change the way it works. Tell your doctor if you are pregnant, planning pregnancy or breastfeeding.