A researcher who has taken the position that the sprays were harmful says he has scientific evidence to back up the claim. Courts, however, have yet to be convinced.
Last summer, the FDA warned consumers to stop using three zinc-containing Zicam products: Zicam Cold Remedy Nasal Gel, Zicam Cold Remedy Swabs, and Zicam Cold Remedy Swabs for kids. The federal regulators cited 130 reports of loss of sense of smell among users of the products.
The analysis included 25 patients treated at the University of California, San Diego Nasal Dysfunction Clinic, which Terrence Davidson directs, who experienced loss of smell after using zinc nasal sprays or swabs to prevent or treat colds. Along with colleague Wendy M. Smith, MD, Davidson applied the nine-point Bradford Hill causation environmental exposure statistical measure to assess the probability that the cold-remedy use caused the loss of sense of smell.
Upper respiratory infections and nasal and sinus disease are major causes of both temporary and permanent loss of smell and diminished sense of smell.
In nearly a dozen cases, however, Courts have found little scientific evidence to support the claim that zinc-containing Zicam nasal products caused loss of smell. Daubert based decisions have resulted in claims not making it to a jury. Davidson himself was rejected as an expert witness when the judge ruled his opinions on specific causation to be “seriously flawed.”
Here's an excerpt from the opinion:
In Rose and Evans (discussed below) Plaintiffs alleged that Defendants' product, Zicam, caused anosmia (loss of smell). Id. at *4. In support of general and specific causation, Plaintiffs in Rose offered the expert testimony of Dr. Terence M. Davidson, a nasal health expert. Id. at *5. In excluding both the general and specific causation opinions of Dr. Davidson, Judge Jon Phipps McCalla noted:
Rose v. Matrixx Initiatives, Inc., No. 07-2404-JPM/tmp, 2009 WL 902311 (W.D. Tenn. Mar. 31, 2009)
Dr. Davidson's opinions on specific causation are seriously flawed as the uncontradicted evidence demonstrates that Rose did not spray the Zicam into her right nostril and thus the Zicam could not have been the cause of her bilateral smell loss. . . .
Dr. Davidson's belief that Rose must have sprayed the Zicam into both nostrils and must have simply forgotten what had happened is not supported by any evidence in the record.
Id. at *16.