A study on Biogen's diranersen found it slowed cognitive decline and has promise in treating Alzheimer's disease, researchers found.

The study provides the clearest evidence yet that medicines like BIIB080 might improve cognition, but leaves unclear why higher doses didn’t perform better.

An experimental drug might help slow early Alzheimer's disease in a markedly different way than current treatments — by lowering the brain's production of a protein called tau.