The U.S. Food & Drug Administration released five guidance documents on Feb. 15 regarding drug development for neurological conditions. The documents clarify FDA’s current thinking on clinical trial design and how to measure a drug’s effectiveness. One notable change is a proposal to evaluate Alzheimer’s drug effectiveness by measuring biomarkers in trial patients before dementia becomes apparent. That’s an important shift for pharmaceutical companies, because hundreds of Alzheimer’s drug trials—most of which recruited people with more advanced disease and looked for cognition improvement—have ended in failure. The failed drugs frequently targeted the two main proteins implicated in the disease: amyloid-β, which forms plaques among brain cells, and tau, which clumps into tangles inside cells. Some companies think the drugs could work if given to people before dementia sets in, but such trials could take decades to run. Instead, companies could look at levels of plaques or tangles to more quickly evaluate whether a drug is working. The idea is contentious, however, because it is still unclear if removing or preventing plaque and tangle formation will prevent Alzheimer’s.