Toxicity of Usnic Acid: A Narrative Review.

Usnic acid (UA) is a dibenzofuran derivative naturally present in lichens, organisms resulting from the symbiosis between a fungus and a cyanobacterium, or an alga. UA shows antimicrobial, antitumor, antioxidant, analgesic, anti-inflammatory as well as UV-protective activities. Its use as pharmacological agent is widely described in traditional medicine, and in the past few years, the product has been marketed as a food supplement for the induction of weight loss. However, the development of severe hepatotoxicity in a limited number of subjects prompted the FDA to issue a warning letter, which led to the withdrawal of the product from the market in November 2001. Data published in literature on UA toxicology, genotoxicity, mutagenesis, and teratogenicity have been reviewed, as well as the case reports of subjects who developed hepatotoxicity following oral administration of UA as a slimming agent. Finally, we reviewed the most recent studies on the topical use of UA, as well as studies aimed at improving UA pharmacologic activity and reducing toxicity. Indeed, advancements in this field of research could open the possibility to reintroduce the use of UA as therapeutical agent.
Competing Interests: N. Croce, M. Pitaro, and G. Antonini are consultants to a company that may be affected by the research reported in the enclosed paper. The company was not involved in any way in manuscript writing, editing, approval, or decision to publish. The authors have disclosed this interest fully to Hindawi, and the authors have in place an approved plan for managing any potential conflicts arising from that involvement.
(Copyright © 2022 Nicoletta Croce et al.)