Extavia is a brand name for the medication interferon beta-1b, which is used in the treatment of multiple sclerosis (MS), a chronic autoimmune disease that affects the central nervous system. Extavia works by modulating the body's immune response, thereby reducing the frequency of relapses and slowing the progression of physical disability associated with MS. It is administered through subcutaneous injections, typically recommended to be taken every other day. Like other interferon medications, Extavia can cause side effects such as flu-like symptoms, injection site reactions, and liver function abnormalities. It is important for patients to be closely monitored by their healthcare provider while on this medication to manage any potential side effects and to adjust treatment as necessary.