Remember the Zicam debacle? To catch you up, Zicam has been promoted for years as a “homeopathic cold remedy”. It is of course neither. Since it contains measurable amounts of zinc, it isn’t “homeopathic”, and since there is no cure for the common cold, it’s not a remedy. In addition to having neither of it’s promoted qualities, the FDA has received hundreds of reports of people losing their sense of smell (became “anosmic”) after using intranasal Zicam. As Steve Novella has pointed out, there is some scientific evidence pointing to a causal connection between zinc and anosmia. Now evidence is pointing toward possible mechanisms.
Adverse drug events are reported all the time. Nailing down whether they are significant can be difficult. First, there must be a plausible connection between the drug ingestion and the adverse event. Then cases have to be studied statistically to see if there is a true causal relationship. This is more difficult for Zicam since it has historically been more or less unregulated, being part of the homeopathic pharmacopoeia and not subject to the same regulation as other drugs (despite not being truly homeopathic). Despite this, the number of reports about Zicam was concerning enough for the FDA to issue a warning.
Lim, J., Davis, G., Wang, Z., Li, V., Wu, Y., Rue, T., & Storm, D. (2009). Zicam-Induced Damage to Mouse and Human Nasal Tissue PLoS ONE, 4 (10) DOI: 10.1371/journal.pone.0007647