I take 20mg of cetrizine hydrochloride (reactine brand) every morning.... i then took a couple hours later a 25mg benadryl (diphenhydramine) for a mild skin itch and di?

Combination antihist: It is not clear that combining antihistamines produce better results. The only guarantee is usually more side effects. Cetirizine is effective at 10mg but works better at 20mg daily (split dose). If you give more it doesn't work a lot better but you do see more sedation. Diphenhydramine is more sedating at ANY dose compared to drugs like cetirizine loratadine fexofenadine.