Diphenhydramine is classified as an antihistamine, antiemetic, sedative, and hypnotic. It is also an anticholinergic deliriant in high doses ( 150-800 mg's). Some people consider it recreational in these high doses but the uncomfortability of the high keeps it's abuse potential to a minimum. DPH is also used recreationally in lower doses (25-100mg's) in combination with opiates and benzodiazepines for it's potentiation abilities.
"Omg DPH is soo hot, I hope he picks me to fuck tonight"