ask your pharmacist

What is the difference between prescription and over-the-counter antihistamines?

Over-the-counter antihistamines include diphenhydramine (brand names Benadryl, >Allerest, and >Contac), doxylamine (>Alka-Seltzer Cold & Sinus), clemastine (>Tavist), and chlorpheniramine (>Chlor-Trimeton).Antihistamines available by prescription include loratadine (>Claritin), fexofenadine (>Allegra), and cetirizine (>Zyrtec).

The main difference between over-the-counter and prescription antihistamines is in their risk of causing drowsiness. In general, prescription antihistamines cause less drowsiness--although Zyrtec may cause more drowsiness than Claritin or Allegra. Nonprescription antihistamines cause drowsiness to varying degrees, with diphenhydramine and doxylamine more likely to cause drowsiness than clemastine and chlorpheniramine.

Since it’s hard to predict how an antihistamine will affect each person, you may have to try several before finding one that works best for you. Most people with mild allergies will do fine with an over-the-counter antihistamine. If you need to be alert--for example, to drive a car or operate heavy machinery--a prescription antihistamine is the safer choice.

Sources:
Allegra product information. Aventis Pharmaceuticals, 2001.
Claritin product information. Schering Corporation, 2001.
Handbook of Nonprescription Drugs. American Pharmaceutical Association, 2000.
Micromedex Healthcare Series. Micromedex, Inc., 2001.
Zyrtec product information. Pfizer, 2001.

This answer prepared 7/2/01.