Biogen Plunges More Than 25 Percent on Alzheimer’s Setback (2)

Biogen Inc. plummeted after the biotechnology giant said that its experimental Alzheimer’s drug was unlikely to be effective and that it was halting its research, in another setback for drugmakers’ efforts to find a therapy for the degenerative ailment.

Shares dropped 27 percent to $233 in premarket trading in New York, shearing off more than a quarter of the company’s market value, which had been $63 billion at the close of trading on March 20.

The development is a “transformative failure for Biogen’s pipeline,” said Brian Abrahams, an analyst at RBC Capital Markets, who had the equivalent of a hold ...