In a society that savours convenience, parents are sometimes tempted (or pressured) to use over-the-counter cold and allergy drugs to get their children to sleep.

In a widely reported incident in the US, a Georgia woman and her talkative 19-month-old son were removed from a flight to Oklahoma after the toddler kept repeating, "Bye-bye, plane!" during the safety demonstration, the annoyed flight attendant suggested a dose of Benadryl, and the mother took offense.

Whatever the merits of that confrontation, doctors say there is one lesson to take away: drugs like Benadryl should never be given to sedate a child.

For one thing, they can have side effects, including constipation and respiratory problems. And for another, in some children they produce the exact opposite of the desired effect.

"Instead of becoming sleepy they can become very animated and less controllable," said Charles J. Cote, a pediatric anesthesiologist at Harvard Medical School.

That paradoxical reaction to the antihistamines contained in many common cold medicines and allergy remedies occurs in as many as 5 percent to 10 percent of children, some experts say. It is not medically dangerous, but it can take a couple of hours to wear off. Indeed, the fine print on these drugs' labels warns of possible "excitability."

Nevertheless, the use of such medicines to make children drowsy is widespread. "Inappropriate use clearly is a very common practice," said Philip Walson, a professor of pediatrics and pharmacology at Cincinnati Children's Hospital Medical Center.

Not safe

Philippe Similon, a pediatrician in Manhattan, says the question of how to travel with young children, and whether it is safe to give them nonprescription sedatives, has become one of the most common in his practice.

Cote and other experts say that while children under 2 tend to have the hardest time staying put in a confined space, they are also the most vulnerable to overdoses and respiratory problems. If a sleeping child's airways become blocked -- by a nose pressed against a seat for example -- the sedation can blunt the natural reflex to shift position.

"There are no real safe sedatives to give children just sort of over-the-counter," Walson said. "Sedation is a big deal."

Walson was an expert witness in the 2005 trial of a Montana day care operator who was convicted of negligent homicide in the death of a 1-year-old in her care. The jury found she had given children an over-the-counter allergy medicine to get them to nap. "It turned out she'd been buying quarts of it, literally, and giving it to all the babies," Walson said.

Not sedatives

Most popular allergy and cold medicines were not developed as sedatives; the recommended doses on their labels are meant for their intended use.

Moreover, the Food and Drug Administration has begun a long-sought review of popular nonprescription cough and cold medicines marketed for children as young as 2, in response to concerns that they have caused several serious health problems.

The drugs, which include Toddler's Dimetapp, Triaminic Infant and Little Colds, were approved for sale years before the FDA began requiring rigorous pre-market testing, and they were never adequately tested in children.

Not tested

Diphenhydramine, the main compound in Benadryl, also predates current drug agency standards and was never tested in children, but it is lower on the review's list of priorities, said Wayne Snodgrass, a professor of pediatrics, pharmacology and toxicology at the University of Texas Medical Branch at Galvestonand chairman of the committee on drugs for the American Academy of Pediatrics.

McNeil Consumer Healthcare,which makes Benadryl, said in a statement that the drug was intended to relieve the symptoms of allergies and colds, and added, "We do not recommend nor condone the use of any of our products for purposes other than those indicated on the label."