Diphenhydramine aka Benadryl is used for allergic reactions, to prevent or treat active motion sickness, and for mild cases of Parkinsonism. The last two uses (motion sickness and Parkinsonism) are based on the anticholinergic effects of diphenhydramine, and not its antihistamine effects. So Benadryl helps Parkinsons.
But Alzheimers medication is just the opposite.
These medications, such as donepezil (Aricept) work by inhibiting the breakdown of acetylcholine, which sends signals in the nervous system. By contrast, anticholinergics—such as diphenhydramine (Benadryl) —block the action of acetylcholine. So if I give mom Benadryl and she gets more confused, is that a hint she has Alzheimer's?