In infants and children, especially, antihistamines in overdosage may cause hallucinations, convulsions, or death. As in adults, antihistamines may diminish mental alertness in children. In the young child, particularly, they may produce excitation.
Antihistamines are more likely to cause dizziness , sedation , and hypotension in elderly patients.
Information for Patients Patients taking diphenhydramine hydrochloride should be advised that this drug may cause drowsiness and has an additive effect with alcohol. Patients should be warned about engaging in activities requiring mental alertness such as driving a car or operating appliances, machinery, etc. Carcinogenesis, Mutagenesis, Impairment of Fertility Long-term studies in animals to determine mutagenic and carcinogenic potential have not been performed. Pregnancy Pregnancy Category B. Reproduction studies have been performed in rats and rabbits at doses up to 5 times the human dose and have revealed no evidence of impaired fertility or harm to the fetus due to diphenhydramine hydrochloride. There are, however, no adequate and well-controlled studies in pregnant women.