Proven facts about allergy medications

If your nose runs, your eyes itch or you break out in hives because of pollen, dust or any other allergen, you can blame histamine. Antihistamines first went on sale in the 1940s, but now a new generation of these histamine blockers, with fewer side effects, has flooded the market. Here are some interesting facts about the newer medicines.

They don't work any better but they are safer because you're less likely to doze off at the wheel. For decades, the only antihistamines on the market were strong — and sedating. These older medications are made up of small molecules that pass easily through the blood-brain barrier, the layer of blood vessels that controls what enters the brain. As a result, the older antihistamines cause drowsiness and poor concentration in 20 to 35 percent of users. The newer antihistamines are made up of larger molecules that are less likely to cross the blood-brain barrier and cause drowsiness. Doctors and pharmacists generally agree the older drugs do a better job of erasing allergy symptoms.

Older antihistamines do work as sleep aids, but be warned: these drugs actually keep some people awake. Most over-the-counter sleep aids are actually antihistamines, usually either diphenhydramine or doxylamine. So, if you can't sleep some night taking an allergy pill may help — but only certain people. For others, it may backfire. Some people (especially children and the elderly) respond to a dose as though they just gulped down a triple espresso, leaving them very much awake.

For some consumers, the older antihistamines remain attractive since they are cheaper and don't require a prescription. Most allergists, however, recommend trying the newer antihistamines first and using the older drugs only if all other treatments fail or if you won't endanger yourself and others by being drowsy.