Rebif (Interferon beta-1a)

Rebif (interferon beta-1a) is an under-the-skin injection therapy for relapsing forms of multiple sclerosis (MS). It reduces the frequency of disease exacerbations, and delays the accumulation of physical disability caused by these flares.

Relapsing-remitting multiple sclerosis (RRMS) is the most common form of MS, representing about 85% of all cases. It is characterized by moments of crisis (exacerbation) followed by periods of symptom relief. These relapse phases may last hours or days.

Doctors also prescribe Rebif to treat people with active secondary progressive MS (active SPMS) and clinically isolated syndrome (CIS).

Rebif is marketed by EMD Serono (known as Merck KGaA outside the U.S. and Canada).

How does Rebif work?

MS is an autoimmune disease that affects nerve cells in the brain and spinal cord. Increased inflammation damages the myelin sheath (the protective coating that surrounds nerve fibers) that allows rapid transmission of the electrical impulses nerves use to communicate. The loss of myelin slows, or stops, these impulses and damages nerve cells.

Interferon beta-1a is a signaling molecule that the immune system normally produces to help fight infections. Scientists don’t fully understand the precise mechanism by which Rebif works to treat MS. However, they know that it signals to different types of immune cells, changing how they respond to threats, to lessen inflammation.

By reducing inflammation, Rebif can decrease attacks on the myelin sheath, easing disease symptoms.

Rebif in clinical trials

A clinical trial, conducted in the 1990s in nine countries, randomized 560 patients with RRMS to either 22 micrograms (mcg) or 44 mcg of Rebif, or a placebo. Data from the study showed that Rebif treatment significantly reduced the number and severity of exacerbations over two years. It also delayed disability progression.

In another study, researchers compared Rebif to a placebo in 515 people who had a single attack of demyelination. In this study, participants received either 44 mcg of Rebif (once or three times a week) or a placebo for two years. Researchers evaluated the time it took for patients to develop MS. Results showed that patients treated Rebif three times a week had a 62.5% probability of developing MS, while those given placebo had an 85.8% probability.

Other information

The U.S. Food and Drug Administration (FDA) first approved Rebif, at 22 mcg or 44 mcg injected three times a week, in 1996.

The FDA updated Rebif’s label for women who are or are considering becoming pregnant and breastfeeding in June 2020. Section 8.1 in the new Rebif label no longer carries the pregnancy Category C designation. This change is intended help healthcare providers weigh treatment risks, and to support the counseling of pregnant women and nursing mothers.

Rebif can cause side effects including irritation and infection at the injection site. Other common side effects are flu-like symptoms, abdominal pain, depression, elevated liver enzymes, and blood disorders (hematologic abnormalities).


Last updated: June 5, 2020


Multiple Sclerosis News Today is strictly a news and information website about the disease. It does not provide medical advice, diagnosis or treatment. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website.

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