Interferon beta drugs were the fifth largest selling class of biological products, with total sales in 2005 estimated at $3.845 billion.

Natural interferon is a protein produced by the body's cells in response to viral infections. There are three types: alfa, beta and gamma.

Genetically engineered interferon beta mimics the activity of naturally-occuring interferon beta produced by the body. The drug is primarily used to decrease the number of episodes of symptoms and slow the development of disability in patients with relapsing-remitting (symptoms come and go) multiple sclerosis.

The leading interferon beta biologics are: