Biogen Idec Inc. said Thursday it is halting efforts to develop dexpramipexole, an experimental drug to treat ALS, the progressive neurodegenerative disorder, after the drug candidate proved ineffective in clinical trials.

The move was a blow to efforts to advance treatments amyotrophis lateral sclerosis, also called Lou Gerhig’s disease, for which there is currently no cure. It was also a setback to the Weston-based biotechnology company, which had invested in the high-risk development program.

Shares of Biogen Idec, which tumbled Thursday morning, were trading down 0.8 percent at $148.60 on the Nasdaq stock exchange shortly after 1: 30 p.m.

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In a statement, Douglas E. Williams, executive vice president of research and development at Biogen Idec, said, “We share the disappointment of members of the ALS community, who had hoped that dexpramipexole would offer a meaningful new treatment.”

Nonetheless, said Williams, the company remains committed to advancing ALS science, working with researchers around the world.