How much Benadryl is lethal?

In pediatric patients, especially, an overdose of antihistamines may cause hallucinations, convulsions, or death. In adults, antihistamines may diminish mental alertness in pediatric patients. Young pediatric patients may produce excitation.

Information relating to lethal doses of medications are available to most toxicologists and pharmacologists, but are rarely published due to the potential for use in intentional harm to self or others.