Antihistamines can be roughly divided into topical and systemic. There is only one topical antihistamine, Astelin, which is a nasal spray has proven beneficial to some. It can still be mildly sedating and has a bad taste.Systemic antihistamines can be roughly divided into sedating and non-sedating types. Interestingly, the sedating ones are over-the-counter, while the safer non-sedating antihistamines are generally prescription. This is all economically-based.
Many brands of antihistamines are now available over-the-counter.
The main side effect of OTC antihistamines is drowsiness.
OTC antihistamines are overused, and should only be used to treat the appropriate symptoms.