An experimental Alzheimer's drug from Biogen, one with a novel approach, slowed decline at comparable rates as approved drugs in a mid-stage study.

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.