Biogen shares plummet 25% after company ends Alzheimer's trials

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 neurodegenerative ailment.

Shares dropped as much as 29 percent in heavy trading, knocking about $18 billion out of the company’s market value and marking its biggest intraday stock drop since 2008.

The Cambridge, Massachusetts-based company and partner Eisai Co. said Thursday that they would discontinue two late-stage trials designed to evaluate the efficacy and safety of the drug, aducanumab. The results showed that the drug