Abstract
Diphenhydramine is a first-generation antihistamine medication. Acute intoxication with diphenhydramine can be severe and potentially fatal. The current case is of a 13-year-old girl who presented with central nervous system depression after voluntary intake of unknown drugs. Serum concentration analysis showed diphenhydramine intoxication, blood half-life extension, and a false positive result for tricyclic antidepressants (TCAs) in urine examination. To our knowledge, this is the first reported case of confirmed diphenhydramine overdose with a false positive result for TCAs and measurement of the serum level in a child. Considering the similarities between the clinical symptoms of diphenhydramine and TCA intoxication, this case illustrates that all physicians should consider the possibility of cross-reactivity during the diagnosis of patients with unknown acute drug intoxication who test positive for TCAs.