The fulvestrant injection 250mg is particularly used for the treatment of certain types of breast cancer. The injection helps to inhibit the production of estrogen hormone which is responsible for the growth of cancer cells in the breast. Some common side effects which disappear as the body get adjusted to the medicine include bone pain, constipation, weakness, nausea, vomiting, loss of appetite, and many more. The injection should be given intravenously to your buttock.