Interferon beta-1b injection is used to reduce episodes of symptoms in patients with relapsing-remitting (course of disease where symptoms flare up from time to time) of multiple sclerosis (MS, a disease in which the nerves do not function properly and patients may experience weakness, numbness, loss of muscle coordination and problems with vision, speech, and bladder control). Interferon beta-1b is in a class of medications called immunomodulators.