Regulatory and legal notices

FDA warning letters explained

Last checked 6 November 2026 · 5 sources

Short answer

An FDA warning letter tells a firm that the agency believes it has committed significant violations of federal requirements ². The FDA's Regulatory Procedures Manual calls it informal and advisory ¹. It does not commit the FDA to enforcement action ¹. The letter usually asks for a written response within 15 working days of receipt ¹. Redacted letters are posted on the FDA website ¹. A close-out letter may follow once the FDA has verified the corrections ².

Issued by: US Food and Drug Administration ²
Legal status: Informal and advisory, not final agency action ¹
Threshold: Violations of regulatory significance ¹
Usual response time: 15 working days after receipt ¹
Where published: FDA Warning Letters page, redacted ^1,3
Close-out: After corrections are made and verified ²

What a warning letter is

The FDA sends a warning letter when it believes there are significant violations of federal requirements ². The letter can point to poor manufacturing practices, problem product claims or wrong directions for use ². The recipient gets a chance to respond and can explain its reasoning if it disagrees ².

The FDA's Regulatory Procedures Manual, Chapter 4, sets out the agency's view. It says a warning letter is informal and advisory ¹. It says warning letters are issued only for violations of regulatory significance ¹. It calls the warning letter the agency's principal means of achieving prompt voluntary compliance with the Federal Food, Drug, and Cosmetic Act ¹.

A warning letter does not commit the FDA to taking enforcement action ¹. The FDA does not treat it as final agency action that can be challenged in court ¹. The agency can still take other enforcement steps, depending on the circumstances ¹.

How it differs from a Form 483 and an untitled letter

The documents look alike to outsiders but sit at different stages.

The Form 483 is reviewed with senior management at the close of the inspection ⁴.
The FDA weighs the Form 483 with the inspection report, evidence and company responses before deciding on further action ⁴.
An untitled letter has no warning statement that failure to correct may lead to enforcement ¹.

Document	When it is issued	What it means
Form FDA 483	At the end of an inspection ⁴	Investigators' observations of conditions that may violate the law. Not a final agency determination ⁴
Untitled letter	After FDA review ¹	Cites violations below the threshold for a warning letter and requests, not requires, a response ¹
Warning letter	After FDA review ¹	Violations of regulatory significance. Usually asks for a response within 15 working days ¹
Close-out letter	After corrections are verified ²	The FDA has checked the corrective actions. Applies to letters issued on or after 1 September 2009 ²

Response and close-out

A warning letter asks for a written response within a set period after receipt, usually 15 working days ¹. Recipients may ask the FDA to post their response with the letter, and the FDA keeps the right not to post some responses ¹.

A close-out letter will not be issued based on representations that some action will be or has been taken ². The corrections must be made and verified, usually by a follow-up inspection ². No close-out letter issues if the violations cannot be corrected ². A close-out letter does not end the duty to stay in compliance, and later inspections can lead to enforcement ¹.

Where warning letters are published

The manual says all FDA-issued warning letters, in redacted form, should be posted on the FDA Warning Letters page ¹. The FDA removes a letter only if it is rescinded or amended ¹. Before a letter is posted, people who want it are directed to file a Freedom of Information Act request ¹.

The online list can be filtered by issuing office, letter issue date, posted date, year and whether a response or close-out letter exists ³. Results can be downloaded as a spreadsheet ³. The FDA notes that matters in a letter may have been the subject of later interaction with the agency ³. Some letters are redacted or edited to remove confidential information ².

Warning letters and recalls

A warning letter is not a recall. FDA recalls are a separate action, conducted on a firm's own initiative, by FDA request or by FDA order ⁵. Recalls are sorted into Class I, II and III by the level of health risk ⁵.

Common questions

Is an FDA warning letter a final decision?

No. The FDA calls it informal and advisory and does not treat it as final agency action ¹.

How long does a firm have to respond to a warning letter?

The letter usually asks for a written response within 15 working days of receipt ¹.

What is the difference between a Form 483 and a warning letter?

A Form 483 lists investigators' observations at the end of an inspection and is not a final agency determination ⁴. A warning letter follows FDA review and covers violations of regulatory significance ¹.

What is a close-out letter?

A letter the FDA may issue after it has verified that the violations in a warning letter were corrected ².

Where can I read FDA warning letters?

On the FDA Warning Letters page, which can be filtered and downloaded ³.

Rules and charges change. Check the official source linked on this page before you pay or travel. Spotted an error? Email hello@noticeofrecord.com.

Sources

What a formal notice is
What makes a notice formal: who gives it, who receives it, the deadline and the form. Breach, recall, regulatory, layoff and court notices compared.
Product recall notices compared
How recall notices work at the US CPSC, FDA and NHTSA, UK OPSS, EU Safety Gate, Australia's ACCC and Health Canada, and where each list is published.
How to check whether a notice was given
Where to look up official notices: state breach lists, the HHS breach portal, SEC EDGAR, FDA warning letters, FCA notices, WARN reports and recall lists.
FCA warning notices and decision notices explained
How UK FCA warning, decision and final notices work, the Regulatory Decisions Committee, the Upper Tribunal and the FCA Warning List.