Can I inject my own interferon? Do I have to go to the hospital to get an injection? There are different dosage forms of interferon, some of which are powders that need to be dissolved in water for injection and then injected. When injecting water for injection, care should be taken to avoid the formation of foam that may affect the inhalation of the drug into the syringe, but more and more manufacturers are now using aqueous formulations and pre-filling the syringe. Should it be injected intramuscularly or subcutaneously? Interferon is mostly injected subcutaneously. Is the injection site in the arm or buttocks? Or is it some other part of the body? The usual interferon injection site is mostly the upper arm, but pegylated interferon (long-acting) is injected subcutaneously in the abdomen or outer thigh.