FDA has denied a request by a U.S. senator to hold a hearing regarding an ingredient widely sold in dietary supplements.

U.S. Sen. Michael Lee (R-Utah) requested FDA schedule a public hearing to clarify its position on the use of N-acetyl-L-cysteine (NAC) in supplements.

In a letter notifying the senator that his request was denied, FDA official Andrew Tantillo stated FDA is reviewing a citizen petition filed by the Council for Responsible Nutrition (CRN). He noted interested persons may submit comments on CRN’s petition, which concerns the regulatory status of NAC.

FDA asserted in 2020 warning letters that NAC cannot be lawfully marketed in a dietary supplement because it was first approved as a drug in 1963. Industry representatives have urged FDA to reverse its position. 

In a July 27 letter to FDA Acting Commissioner Janet Woodcock, Lee requested a Part 15 hearing and asked the agency to answer detailed questions related to NAC, including the specific date FDA identified the ingredient being used as both a drug and supplement in the U.S.

“The agency will consider all comments submitted to the open docket in making a determination on the [CRN] citizen petition,” Tantillo wrote to Lee in the Aug. 19 letter. “FDA denies the hearing request because the agency does not believe that such a hearing is necessary at this time given the other mechanisms at stakeholders’ disposal to interact with FDA on this issue, including submission of comments to the docket for the citizen petition.”

Related:US senator, NPA press FDA on NAC supplements

FDA denied the senator’s request just one day after receiving a separate citizen petition related to NAC from the Natural Products Association (NPA).

The agency in recent years has held Part 15 public hearings on a wide array of issues—from products containing cannabis-derived compounds to homeopathic product regulation, nicotine replacement therapies and use of fecal microbiota for transplantation to treat Clostridium difficile (C. diff).

Tantillo, FDA’s acting associate commissioner for legislative affairs, did not answer Lee’s questions regarding NAC. But he said FDA would provide Lee’s staff additional information after the agency has addressed the petition related to NAC.

“How does the agency not respond to Senator Lee’s questions?” wondered Dan Fabricant, president and CEO of NPA, in an interview. “He asked questions that are relevant to implementation of law. What does that mean for the rest of us in terms of getting an answer?”

Staff members for Lee did not immediately respond to a request for comment.

A former FDA official offered a possible reason why FDA denied the senator's request for a hearing. FDA is usually prohibited from publicly discussing a specific matter that's the subject of a citizen petition, according to Bob Durkin, of counsel with the law firm Arnall Golden Gregory LLP (AGG), who previously served as deputy director of FDA's Office of Dietary Supplement Programs (ODSP).

Since FDA has received citizen petitions from CRN and NPA on NAC, "I can understand if that's the case," he added. 

Durkin also said he wondered whether FDA's letter to Lee signaled the agency "intends to do something about NAC shortly and then circle back to the senator and explain that’s why they refused the meeting.”