REBIF is a brand-name prescription medication that is primarily used in the treatment of relapsing forms of multiple sclerosis (MS), a chronic autoimmune disease affecting the central nervous system. It belongs to a class of drugs known as interferon beta-1a, which are synthetic versions of proteins that naturally occur in the body. REBIF works by modulating the body's immune response to help reduce the frequency of relapse episodes and slow the progression of physical disability associated with MS. It is administered through subcutaneous injections, typically three times a week, and its use may be associated with side effects such as flu-like symptoms, injection site reactions, and liver function abnormalities. Patients are usually monitored closely by healthcare professionals to manage these potential side effects and to ensure the effectiveness of the treatment.