Data is still emerging. But according to a recent JAMA Neurology article, about four out of ten of early Alzheimer's patients on Aduhelm participating in phase 3 studies got ARIA-E (brain swelling) or ARIA-H (brain bleeding). Some suffered ARIA symptoms including: headaches, dizziness, nausea, confusion/mental disorientation. At worst, ARIA can result in a seizure, stroke, or death.