SNIP “If you take diphenhydramine, also known as Benadryl or Elavil, or any sort of antihistamine medication or anticholinergic for a long period of time, it has been linked to dementia,” Hasan said. Benadryl is an over-the-counter antihistamine used to relieve symptoms of hay fever, allergies and the common cold. Research has shown a link between an increased risk of dementia and long-term use of Benadryl and other anticholinergic drugs that block acetylcholine, a neurotransmitter crucial for muscle contractions and important brain functions like learning and memory.