The effect of diphenhydramine alone and in combination with ethanol on histamine skin response and mental performance.

The effects of diphenhydramine and diphenhydramine plus ethanol on response to intradermal histamine and on mental performance were assessed in twelve male volunteers. A significant impairment of histamine skin response was found with diphenhydramine. This response was unaffected by ethanol. Ethanol improved performance with a tracking test compared with diphenhydramine alone, the effect was not potentiated by the combination. None of the treatments had a significant effect on a digit symbol substitution test. Co-administration of ethanol and diphenhydramine caused greater impairment of performance in a serial seven subtraction test than diphenhydramine alone. There was no correlation between central and peripheral effects of the antihistamine.