The Food and Drug Administration last year warned consumers to stop using Zicam Cold Remedy Nasal Gel and Zicam Cold Remedy Nasal Swabs, popular homeopathic remedies that contain zinc. Matrixx Initiatives of Scottsdale, Ariz., which markets the products, has denied the zinc gels cause anosmia, and called the conclusions "scientifically unfounded and misleading." But the company did recall both products, which have been the subjects of hundreds of lawsuits.
The authors, Dr. Terence M. Davidson and Dr. Wendy M. Smith, applied nine criteria used in 1965 by Sir Austin Bradford Hill to demonstrate a causal link between smoking and lung cancer. The Bradford Hill criteria include an examination of the strength of the association between the risk factor and the disease, as well as the consistency, specificity, relationship in time, biological plausibility and experimental evidence, and whether greater exposure is associated with more disease.
Davidson, director of the nasal dysfunction clinic at the University of California, San Diego, said there is no danger from zinc gluconate taken orally but said that when it is sniffed through the nose it can burn olfactory tissue.
Bill Hemelt, chief executive of Matrixx Inc., said the product was safe. "The common cold is the No. 1 cause of loss of sense of smell, and naturally people who use the product and have a cold are misattributing the result to our product."