Try it when: You need immediate relief from mild to moderate symptoms and you don’t have time to consult your doctor.
How it works: Over-the-counter (OTC) remedies, like Claritin, Zyrtec, and Benadryl (and prescription versions, such as Allegra), have various ingredients to block receptors on the blood vessels that released histamines would inhabit. “It’s like putting gum in a lock,” says Sublett. Take one tablet two hours before entering an allergy red zone and use as directed until your symptoms abate.
Good to know: Some OTC antihistamines cause side effects, including dry mouth and a spacey state of mind.