Biogen's only drug, the multiple sclerosis fighter Avonex, is under heavy fire from Serono's Rebif.

FORBES: Skin Deep

Additionally, adverse events like diarrhea, hair thinning and back pain were more common in patients treated with Rebif.

FORBES: European Pharma Stocks Hit on Bad News

There's a new competing drug just out called Rebif from Swiss biotech outfit Serono, which has teamed up with pharmaceutical marketing powerhouse Pfizer.

FORBES: Biopipeline