The potential benefit of the anti‐amyloid drug aducanumab based on results of recent EMERGE and ENGAGE clinical trials has generated great controversy and has very important implications for the future of anti‐amyloid drug therapies. The two trials of 18‐month duration were done in patients with mild cognitive impairment (MCI) and early dementia. The ENGAGE trial showed no benefit while the high‐dose EMERGE trial initially also showed no benefit but with longer follow‐up there was a significant positive benefit. A recent review form the U.S. Food and Drug Administration (FDA) Advisory Committee was negative while the FDA Office of Neurological Drugs was positive and the statisticians negative. This has generated debate about whether the drug should be approved, disapproved, require a new clinical trial, or approved for a subsample only. The implications for treating both MCI and Alzheimer's disease (AD) patients with anti‐amyloid drugs is very substantial as well as the brain amyloid‐AD‐dementia hypothesis.