U.S. Food and Drug Administration (FDA) Lets N-Acetylcysteine Supplements Stay on Shelves While Ruling N-Acetylcysteine Is Legally a Drug (2022)

Table of Contents

1. What the U.S. Food and Drug Administration Did in 2022
2. N-Acetylcysteine in the U.S. Food and Drug Administration’s Documents
3. The Legal Rule: When a Drug Ingredient Cannot Be a Supplement
4. The Two Petitions and the March 31, 2022 Answer
5. The April 2022 Draft Guidance
6. The August 2022 Final Guidance: What the Policy Covers
7. Products the Policy Does Not Cover
8. How Long the Policy Is Meant to Last
9. What the Policy Does Not Do
10. Dates and Legal Status as of October 18, 2026
11. How It Fits Other U.S. Food and Drug Administration Supplement-Ingredient Decisions
12. Primary Documents
13. Key Research Papers
14. Connections
15. Featured Videos

1. What the U.S. Food and Drug Administration Did in 2022

The U.S. Food and Drug Administration’s 2022 N-acetylcysteine decisions came in three documents:

• March 31, 2022 — petition response. In a constituent update (a notice the U.S. Food and Drug Administration’s food program posts for industry and the public), the U.S. Food and Drug Administration announced that it had “denied the request in two citizen petitions” asking the agency to determine that products containing N-acetylcysteine are not excluded from the definition of a dietary supplement. The response “confirmed N-acetylcysteine is excluded from the definition of a dietary supplement.”
• April 21–22, 2022 — draft guidance. The U.S. Food and Drug Administration announced a draft guidance, “Policy Regarding N-acetyl-L-cysteine,” and published a notice of its availability in the Federal Register on April 22, 2022 (87 FR 24170). Comments were invited until May 23, 2022.
• August 1–2, 2022 — final guidance. The U.S. Food and Drug Administration announced the final version on August 1, 2022, and the Federal Register notice of availability followed on August 2, 2022 (87 FR 47220). Both notices sit in the same public file, Docket No. FDA-2022-D-0490.

The Federal Register is the U.S. government’s daily publication of rules, proposed rules and official notices. A docket is the public file for an action, where its documents and the public comments on it are kept on regulations.gov.

The final guidance describes its purpose as advising “dietary supplement manufacturers, distributors, and other stakeholders of our intent to exercise enforcement discretion with respect to the sale and distribution of certain products that contain N-acetyl-L-cysteine and are labeled as dietary supplements.” Enforcement discretion means the agency states that it does not intend to take action against certain products, even though, in its reading of the law, those products do not meet a legal requirement.

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2. N-Acetylcysteine in the U.S. Food and Drug Administration’s Documents

The final guidance lists the names under which the same ingredient appears: “acetylcysteine; L-acetylcysteine; L-alpha-acetamido-beta-mercaptopropionic acid; N-acetyl cysteine; N-acetyl-3-mercaptoalanine; N-acetyl-L-cysteine; N-acetylcysteine; and mercapturic acid.” It adds: “These names all refer to the same active ingredient.”

Two facts about N-acetylcysteine drive the whole decision, and both come from the guidance:

• It was approved as a drug in 1963. N-acetylcysteine, “i.e., acetylcysteine,” was approved as a new drug under section 505 of the Federal Food, Drug, and Cosmetic Act (FD&C Act) on September 14, 1963; the guidance cites the approval announcement at 28 FR 13509 (December 13, 1963).
• It has long been sold as a supplement. The guidance states that “N-acetylcysteine-containing products represented as dietary supplements have been sold in the U.S. for over 30 years, and consumers continue to seek access to such products.”

The guidance also records the U.S. Food and Drug Administration’s view of safety at that point: “While U.S. Food and Drug Administration’s full safety review of N-acetylcysteine remains ongoing, our initial review has not revealed safety concerns with respect to the use of this ingredient in or as a dietary supplement.”

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3. The Legal Rule: When a Drug Ingredient Cannot Be a Supplement

The FD&C Act is the main federal law the U.S. Food and Drug Administration enforces. The FD&C Act’s definition of “dietary supplement” (section 201(ff)(3)(B), 21 U.S.C. 321(ff)(3)(B)) excludes, among other things, “an article that is approved as a new drug under section 505” that “was not before such approval … marketed as a dietary supplement or as a food unless the Secretary, in the Secretary’s discretion, has issued a regulation, after notice and comment, finding that the article would be lawful under [the FD&C] Act.” A second clause, 201(ff)(3)(B)(ii), applies the same exclusion to ingredients authorized for investigation as new drugs where substantial clinical investigations have begun and been made public.

The guidance sums up the effect: if an ingredient has been approved as a new drug, products containing it are outside the definition of a dietary supplement unless one of two exceptions applies.

1. Marketed first. The ingredient was marketed as a dietary supplement or as a food before the drug approval.
2. A regulation. The U.S. Food and Drug Administration, under authority delegated by the Secretary of Health and Human Services, issues a regulation, “after notice and comment,” finding that the ingredient would be lawful under the FD&C Act.

Applying this to N-acetylcysteine, the guidance states that the U.S. Food and Drug Administration “has determined that N-acetylcysteine is excluded from the dietary supplement definition under section 201(ff)(3)(B)(i) of the FD&C Act because N-acetylcysteine was approved as a new drug before it was marketed as a dietary supplement or as a food.” On the first exception, the U.S. Food and Drug Administration wrote that it “is not aware of any evidence that N-acetylcysteine was marketed as a dietary supplement or as a food prior to September 14, 1963.” That left only the second exception, a regulation, as a way for N-acetylcysteine to become a lawful supplement ingredient.

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4. The Two Petitions and the March 31, 2022 Answer

According to the final guidance, the U.S. Food and Drug Administration received two citizen petitions from two dietary-supplement trade associations, dated June 1, 2021 and August 18, 2021 (Docket Nos. FDA-2021-P-0523 and FDA-2021-P-0938). A citizen petition is a formal written request asking the U.S. Food and Drug Administration to take, or not take, an action. Both asked the agency to conclude that N-acetylcysteine is not excluded from the definition of a dietary supplement. The second petition also asked, in the alternative, that the U.S. Food and Drug Administration support issuing a regulation, after notice and comment, finding that N-acetylcysteine would be lawful — in other words, the second exception described in section 3.

On November 24, 2021 the U.S. Food and Drug Administration sent tentative responses saying it had not reached a decision “because of the complex nature of the requests and ongoing research we are working to complete.” To help it weigh the rulemaking request, it asked interested parties to send the second petition’s docket information “regarding the safe use of N-acetylcysteine as or in dietary supplements and data regarding potential safety concerns.”

On March 31, 2022 the U.S. Food and Drug Administration issued a joint final response. The guidance describes the outcome: it denied the first petition “in its entirety” and denied the second petition’s first request, stating that N-acetylcysteine products are excluded from the dietary supplement definition. It had “not yet reached a final decision” on the alternative request for a regulation and was “considering initiating rulemaking” to permit N-acetylcysteine in or as a dietary supplement.

The March 31 constituent update already pointed toward the policy that followed: “In the interim, in light of the absence of safety concerns based on our review to date, among other factors, the U.S. Food and Drug Administration is considering exercising enforcement discretion for N-acetylcysteine-containing products labeled as dietary supplements.”

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5. The April 2022 Draft Guidance

On April 21, 2022 the U.S. Food and Drug Administration announced the draft guidance, and the Federal Register notice of availability appeared the next day. The constituent update for the draft explained the U.S. Food and Drug Administration’s reasoning in three steps:

• N-acetylcysteine is excluded “because N-acetylcysteine was approved as a new drug before it was marketed as a dietary supplement or as a food.”
• The U.S. Food and Drug Administration was “considering initiating rulemaking to provide by regulation that N-acetylcysteine is not excluded from the definition of dietary supplement,” and added: “If, among other considerations, the U.S. Food and Drug Administration does not identify safety-related concerns as we continue our review of the available data and information, we are likely to propose a rule providing that N-acetylcysteine is not excluded from the definition of dietary supplement.”
• Because its initial review had not revealed safety concerns and N-acetylcysteine products had been sold for over 30 years, “the U.S. Food and Drug Administration issued this draft guidance to explain our policy regarding products labeled as dietary supplements that contain N-acetylcysteine.”

The Federal Register notice (87 FR 24170) gave the public until May 23, 2022 to comment so that comments would be considered before work on the final version began.

A guidance document explains how the U.S. Food and Drug Administration reads and applies the law. The N-acetylcysteine guidance states plainly that its contents “do not have the force and effect of law and are not meant to bind the public in any way, unless specifically incorporated into a contract.”

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6. The August 2022 Final Guidance: What the Policy Covers

The final guidance, dated August 2022 and announced in the Federal Register on August 2, 2022 (87 FR 47220), finalized the April draft. The constituent update of August 1, 2022 states that the enforcement discretion policy “applies to products that would be lawfully marketed dietary supplements if N-acetylcysteine were not excluded from the definition of ‘dietary supplement’ and are not otherwise in violation of the Federal Food, Drug, and Cosmetic Act.”

The guidance gives an example of what the U.S. Food and Drug Administration does not intend to object to. A product that affects “the structure or any function of the body” is, under section 201(g)(1)(C) of the FD&C Act, a drug. Ordinarily, a dietary supplement can carry a truthful, not misleading structure/function statement — the guidance describes it as a statement that “describes the role of a nutrient or dietary ingredient intended to affect the structure or function in humans” — without becoming a drug for that reason. The guidance notes that this protection “does not apply to a product that is or contains an article that is excluded from the definition of dietary supplement, even if such product is labeled as a dietary supplement.”

So, strictly read, an N-acetylcysteine product labeled as a supplement and carrying a structure/function statement is a drug. The policy addresses exactly that: “with respect to the sale of an N-acetylcysteine-containing product that is labeled as a dietary supplement, U.S. Food and Drug Administration does not intend to object solely because the product is intended to affect the structure or any function of the body of man and, therefore, is a drug under section 201(g)(1)(C) of the FD&C Act.”

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7. Products the Policy Does Not Cover

The final guidance draws two limits:

• Disease claims. The policy “does not apply to an N-acetylcysteine-containing product that is labeled as a dietary supplement but is intended for use in the diagnosis, cure, mitigation, treatment, or prevention of disease and, therefore, is a drug under section 201(g)(1)(B) of the FD&C Act.”
• Other violations. It does not apply “to N-acetylcysteine-containing products that are adulterated or misbranded under the FD&C Act (other than those misbranded only because they contain N-acetylcysteine and are labeled as dietary supplements).”

In short, the policy sets aside only the problem created by N-acetylcysteine’s drug history; a product that breaks the FD&C Act in any other way is outside it.

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8. How Long the Policy Is Meant to Last

The policy has a stated end point. The final guidance states: “Unless we identify safety-related concerns during our ongoing review, U.S. Food and Drug Administration intends to exercise enforcement discretion until either of the following occurs: we complete notice-and-comment rulemaking to allow the use of N-acetylcysteine in or as a dietary supplement … or we deny the [second] citizen petition’s request for rulemaking.”

The guidance also states that if the U.S. Food and Drug Administration determines the policy “is no longer appropriate,” it will “withdraw or revise this guidance in accordance with 21 CFR 10.115.” The April constituent update phrases the same point as notifying stakeholders “by withdrawing or revising the guidance.”

There are therefore three ways the policy could end, as the documents describe them: a final regulation allowing N-acetylcysteine in supplements (which would replace enforcement discretion with lawful status), a denial of the remaining petition request, or safety concerns found during the U.S. Food and Drug Administration’s review.

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9. What the Policy Does Not Do

• It does not make N-acetylcysteine a lawful dietary ingredient. The U.S. Food and Drug Administration’s March 31, 2022 response confirmed that N-acetylcysteine is excluded from the dietary supplement definition; the guidance describes only the agency’s enforcement intentions and, in its own words, does “not have the force and effect of law.”
• It is not a regulation. Only a regulation issued after notice and comment can bring N-acetylcysteine back within the supplement definition. As of the documents checked for this page, the U.S. Food and Drug Administration had not proposed one (section 10).
• It does not cover disease claims. N-acetylcysteine products labeled as supplements but intended to diagnose, cure, mitigate, treat or prevent disease fall outside the policy.
• It does not excuse other violations. Products that are adulterated, or misbranded for reasons other than containing N-acetylcysteine, are not covered.
• It does not concern prescription acetylcysteine. The policy is about products labeled as dietary supplements; the approved drug is a separate matter.
• It is not a final safety verdict. The guidance reports an initial review that “has not revealed safety concerns” and states that the full safety review “remains ongoing.”

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10. Dates and Legal Status as of October 18, 2026

• September 14, 1963: acetylcysteine is approved as a new drug, per the final guidance.
• June 1 and August 18, 2021: the two citizen petitions are dated.
• November 24, 2021: the U.S. Food and Drug Administration’s tentative responses ask for safety data.
• March 31, 2022: joint final response; N-acetylcysteine confirmed as excluded from the supplement definition; the rulemaking request is left open.
• April 21–22, 2022: draft guidance announced; Federal Register notice 87 FR 24170 (Docket No. FDA-2022-D-0490); comments due May 23, 2022.
• August 1–2, 2022: final guidance announced; Federal Register notice 87 FR 47220 (same docket).
• November 29, 2023: the U.S. Food and Drug Administration adds its systematic review of the literature on N-acetylcysteine to its Peer Review Agenda. The constituent update states that “The agency has completed its review of safety information related to N-acetylcysteine, which will now go through the peer review process as a next step,” and that the review was undertaken as part of its evaluation of the petition’s rulemaking request.

Status as of October 18, 2026: N-acetylcysteine remains excluded from the definition of a dietary supplement; the August 2022 enforcement-discretion guidance is final and, as far as found, still in place. A check of the Federal Register for U.S. Food and Drug Administration documents mentioning N-acetyl or acetylcysteine from August 3, 2022 through October 18, 2026 found no proposed or final rule on N-acetylcysteine in dietary supplements and no notice withdrawing or revising the guidance; the two U.S. Food and Drug Administration documents returned concern other matters (generic-drug guidance and a kidney-biomarker request for information). The U.S. Food and Drug Administration’s constituent update, current as of November 29, 2023, still lists the guidance as final. The outcome of the peer review after November 2023 was not found in the documents checked.

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11. How It Fits Other U.S. Food and Drug Administration Supplement-Ingredient Decisions

The N-acetylcysteine decision turns on section 201(ff)(3)(B) of the FD&C Act, the clause that keeps an ingredient first approved or investigated as a drug out of the supplement category unless it was sold as a supplement or food first or a regulation allows it. The same section is at the centre of a later dispute over another ingredient, reported on the 2025 page on nicotinamide mononucleotide (NMN) in dietary supplements, where the U.S. Food and Drug Administration applied the investigation clause, 201(ff)(3)(B)(ii).

Other U.S. Food and Drug Administration actions on what counts as a lawful supplement ingredient are reported on their own pages: the 2023 public directory of what the U.S. Food and Drug Administration has said about supplement ingredients and the 2026 public meeting on what counts as a dietary ingredient. Among the 2022 actions, the U.S. Food and Drug Administration’s warning letters to supplement sellers over untested stimulants and heart-disease cure claims are reported on their own page. The U.S. Food and Drug Administration’s major 2022 actions reported on these pages are listed on the U.S. Food and Drug Administration Actions of 2022 hub.

Questions about taking N-acetylcysteine or any other supplement are for a clinician; this page reports only the regulatory record.

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12. Primary Documents

1. U.S. Food and Drug Administration. U.S. Food and Drug Administration Issues Response to Two Citizen Petitions on N-acetylcysteine in Dietary Supplements. HFP Constituent Update, March 31, 2022 (with a later note on the final guidance), content current as of April 21, 2022 — fda.gov constituent update, March 31, 2022
2. U.S. Food and Drug Administration. U.S. Food and Drug Administration Releases Final Guidance on Enforcement Discretion for Certain N-acetylcysteine Products. HFP Constituent Update, April 21, 2022, with updates of August 1, 2022 and November 29, 2023 — fda.gov constituent update on the N-acetylcysteine guidance
3. Food and Drug Administration, U.S. Department of Health and Human Services (HHS) (2022). Policy Regarding N-acetyl-L-cysteine: Draft Guidance for Industry; Availability. Notice of availability. Federal Register 87 FR 24170, April 22, 2022. Docket No. FDA-2022-D-0490 — FR Doc. 2022-08560
4. Food and Drug Administration, U.S. Department of Health and Human Services (2022). Policy Regarding N-acetyl-L-cysteine; Guidance for Industry; Availability. Notice of availability. Federal Register 87 FR 47220, August 2, 2022. Docket No. FDA-2022-D-0490 — FR Doc. 2022-16499
5. U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition. Policy Regarding N-acetyl-L-cysteine: Guidance for Industry. August 2022 — fda.gov final guidance (PDF). The guidance’s landing page is listed in the U.S. Food and Drug Administration guidance-documents database as “Guidance for Industry: Policy Regarding N-acetyl-L-cysteine.”
6. Public docket FDA-2022-D-0490 — regulations.gov FDA-2022-D-0490

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Key Research Papers

1. Šalamon Š, Kramar B, Marolt TP, Poljšak B, Milisav I (2019). Medical and Dietary Uses of N-Acetylcysteine. Antioxidants (Basel) 8(5):111 — PubMed PMID: 31035402
2. Tenório MCDS, Graciliano NG, Moura FA, Oliveira ACM, Goulart MOF (2021). N-Acetylcysteine (NAC): Impacts on Human Health. Antioxidants (Basel) 10(6):967 — PubMed PMID: 34208683
3. Schwalfenberg GK (2021). N-Acetylcysteine: A Review of Clinical Usefulness (an Old Drug with New Tricks). Journal of Nutrition and Metabolism 2021:9949453 — PubMed PMID: 34221501
4. Rushworth GF, Megson IL (2014). Existing and potential therapeutic uses for N-acetylcysteine: the need for conversion to intracellular glutathione for antioxidant benefits. Pharmacology & Therapeutics 141(2):150-159 — PubMed PMID: 24080471
5. Heard KJ (2008). Acetylcysteine for acetaminophen poisoning. The New England Journal of Medicine 359(3):285-292 — PubMed PMID: 18635433
6. Deepmala, Slattery J, Kumar N, Delhey L, Berk M, Dean O, Spielholz C, Frye R (2015). Clinical trials of N-acetylcysteine in psychiatry and neurology: A systematic review. Neuroscience and Biobehavioral Reviews 55:294-321 — PubMed PMID: 25957927

The first three papers are reviews of N-acetylcysteine’s medical and dietary uses. The fourth reviews proposed therapeutic uses and the role of conversion to glutathione. The fifth describes acetylcysteine’s established use as a drug for acetaminophen poisoning. The sixth is a systematic review of clinical trials in psychiatry and neurology. None of these papers is a U.S. Food and Drug Administration document, and none was cited by the U.S. Food and Drug Administration in the guidance.

PubMed Topic Searches

1. PubMed: N-acetylcysteine dietary supplement
2. PubMed: N-acetylcysteine safety
3. PubMed: dietary supplement regulation and drug exclusion

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Connections

• U.S. Food and Drug Administration Actions of 2022
• U.S. Food and Drug Administration and Regulation
• N-acetyl-cysteine Research
• Glutathione
• Thiols and Sulfur Compounds
• Supplement Warning Letters (2022)
• Dietary Supplement Ingredient Directory (2023)
• Nicotinamide Mononucleotide Allowed in Dietary Supplements (2025)
• What Counts as a Dietary Ingredient (2026)

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