Diphenhydramine: 300 mg/day from all sources, 50 mg in one dose q 6 hours, it is the most widely used OTC. Other OTC 2nd generation antihistamines as cetirizine , loratadine or fexofenadine have different dosing but can be taken once a day, and do not develop tolerance, as the case with diphenhydramine, with prolonged usage. Don't combine different types unless you ask a physician, wish you wellness
Answered 11/29/2015
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