But parents who have successfully used allergy medicine to help children sleep swear by it, albeit in hushed tones.

BBC: Should parents drug babies on long flights?

Tax breaks for over-the-counter drugs date to 2003, as popular drugs like the allergy medicine Claritin began switching to over-the-counter status.

WSJ: In Health Law, Rx for Trouble

One mother of two who did not wish to be identified used the over-the-counter allergy and motion-sickness medicine Phenergan for a recent flight from Australia to the US. She said the first eight hours of the flight were "agony" and that she used the medication as a last resort to help her three-year-old daughter sleep.

BBC: Should parents drug babies on long flights?

Recently, the asthma pill was approved as an allergy medicine, and Merck is betting that it can convince hay fever sufferers to take it instead of antihistamines like Claritin, available cheap and without a prescription from Schering-Plough (nyse: SGP - news - people ), and Zyrtec, sold with a prescription by Pfizer (nyse: PFE - news - people ).

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