Firmagon is used in the treatment of advanced prostate cancer. It works by lowering the amount of testosterone produced in the body and restricts the growth of a cancer cell. Firmagon is given as an injection under the skin only under the supervision of a doctor. Do not try to self inject the medicine as it might enhance the chances of an accident or get injected into the veins. 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 reactions (pain, swelling, redness), weight gain, hot flashes, increased liver enzyme, and low sexual desire. If these bother you or appear serious, let your doctor know. There may be ways of reducing or preventing them. If you notice dizziness or trouble sleeping, then better to avoid driving or machinery work. Before taking this medicine, tell your doctor if you have ever had heart disease, or diabetes or liver disease. 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 or breastfeeding. Your doctor may check for prostate specific antigen (PSA) level in your blood, to know treatment is working or not.