YES! As with many medicines, both prescription and over-the-counter, it is possible to overdose on Benadryl. Benadryl is one of several brand names for the generic drug diphenhydramine, an antihistamine. You may be taking Benadryl for allergies, or you may be using it to help you fall or stay asleep. If you have taken too much Benadryl, you may notice the following symptoms: confusion, dry mouth, nausea, drowsiness, flushed face, fast heartbeat, diarrhea, feeling agitated, feeling unsteady, or movement problems.
Other people may have trouble understanding you when you speak (this is called incoherence), you may lose track of where you are and what day it is, and you may even lose consciousness.
If you think that you, or someone close to you, may have taken too much Benadryl, call for help right away. If you can, call the Poison Control Center as well. The experts there will be able to tell you what your next steps should be. Do your best to figure out when the person took the Benadryl, how much he took, and his age and weight.