Fulvestrant injection of 250mg is used to treat breast cancer in women who have gone through menopause. It inhibits the production of estrogen hormone which promotes the growth of cancer cells. The common side effects of the medication include nausea, vomiting, allergic reaction, headache, urinary tract infection, and diarrhea. The medicine should be taken by the healthcare professional in a medical facility. However, it is recommended to avoid taking injections during pregnancy and breastfeeding due to the harmful effects on the baby.