Airborne, a dietary supplement that many people take to help prevent and treat the common cold, is getting a lot of buzz.

　　"This stuff works," a young woman told a stranger in a Times Square pharmacy as she reached for one of the last three packages.

　　Sally Firth, 37, a respiratory therapist in Milwaukee, said she recommended the effervescent tablets "to everyone who says hello."

　　Airborne was created by a schoolteacher, Victoria Knight-McDowell, who was tired of getting colds from her students and went on to be a founder of the company, known as Knight-McDowell Labs, which makes the product.

　　Oprah Winfrey recently lauded Airborne on her talk show. Howard Stern did the same on his. The company watched its sales rise to more than $17 million last year, according to Information Resources Inc., which tracks retail sales. And the cold treatment has become America's 10th largest selling multivitamin.

　　Doctors say there is so far no evidence to demonstrate that it does, and many are skeptical about its effectiveness.

　　Knight-McDowell commissioned a small clinical trial, and the results suggest that the product can fight colds, said Rider McDowell, a co-founder of the company. But the study has not been published in a medical journal. Mr. McDowell would not disclose where the study was done.

　　Airborne contains many of the same vitamins, minerals and herbs that are individually cited for fighting colds, including zinc, echinacea, garlic, ginger and a hefty dose (1,000 milligrams) of vitamin C. Many people take these supplements, especially at this time of year, but doctors rarely recommend them.

　　Among those new products are Gesundheit, a skin patch that, like many supplements in pill form, contains vitamins C and A, echinacea and other herbs, and Kleenex Anti-Viral tissues, which the manufacturer claims kill 99.9 percent of viruses they come in contact with.

　　Although most cold-prevention supplements are harmless, uncomfortable side effects may result from taking hefty doses. Even large amounts of vitamin C, a water-soluble vitamin easily excreted through urine when people take more than the body can readily absorb, can cause diarrhea, stomach inflammation or, rarely, kidney stones. "Is that worth it, given that we don't have strong evidence that vitamin C does any good against colds?" asked Dr. Susan Meacham, associate professor of nutrition at the University of Nevada at Las Vegas.