How common is a diphenhydramine symptomatic overdose in the u.s.?

Toxicity: Every human body reacts to a drug differently. In some children, even one dose of Benadryl (diphenhydramine) will make them very hyper (known as a paradoxical reaction). First and foremost, you should always follow the labeled instructions on all otc medications. If still unsure, speak to your physician. Otc med overdoses are fairly common in the usa.