Correction: An earlier version of this news brief stated that FDA rejected NPA’s citizen petition. While FDA denied NPA’s request that the agency reverse its position that products containing NAC are excluded from the definition of a dietary supplement, NPA’s petition was not entirely rejected in that the agency said it would consider rulemaking to permit use of NAC in or as a dietary supplement. 

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The U.S. Food and Drug Administration (FDA) has completed a review of safety information related to N-acetyl-cysteine (NAC). The agency’s analysis will now undergo peer review.
 
This development follows a years-long dispute that began when FDA proclaimed in warning letters that NAC is excluded from dietary supplements due to its approval as a drug in 1963.
 
Amid uproar from the dietary supplements industry, the Council for Responsible Nutrition (CRN) filed a citizen petition requesting the agency reverse its position, but FDA denied that request.
 
The Natural Products Association (NPA) also filed a citizen petition and sued the agency for declaratory and injunctive relief based on what it alleged was an unlawful retroactive application of the Food, Drug, and Cosmetic Act. 
 
While FDA denied NPA’s request that the agency reverse its position that products containing NAC are excluded from the definition of a dietary supplement, the agency said it would consider rulemaking to permit use of NAC in or as a dietary supplement.
  
NPA dropped the suit after FDA finalized guidance that said the agency would exercise enforcement discretion and not take action against products containing NAC that didn’t otherwise violate any regulations.
 
While FDA has posited that NAC is excluded from meeting the definition of dietary supplements in the past, the agency has consistently noted that all available safety data indicates there aren’t any safety concerns under typical conditions of use in healthy adults.
 
The NAC controversy is a familiar refrain. In the past few years, the agency has made similar proclamations about several other ingredients like NMN and CBD due to the “drug preclusion” clause of the Dietary Supplements Health and Education Act (DSHEA), which doesn’t allow any substance to be classified as a dietary ingredient if it was approved as an investigational new drug prior to being marketed as such.