Warning Letter

A warning letter is FDA’s formal notice that it considers a firm to have significantly violated the law, and it is a substantial escalation from a 483. It is issued after agency review rather than by the investigator, it is published on FDA’s website, and it typically requires a written response within fifteen working days. It also states plainly that failure to correct may result in further action without notice.

The consequences reach well beyond the letter. Warning letters can precede import alerts (detention without physical examination), seizure, injunction, or a consent decree; they can stall pending applications, since FDA may withhold approval of applications listing the cited facility; and they are read by customers, partners, and investors because they are public. For a contract manufacturer, one can be commercially decisive.

What FDA looks for in a response is scope and system, not apology. The strongest responses address the underlying systemic condition rather than each cited instance, assess how far the problem extends across products and time — including a retrospective review where data reliability is in question — commit to independent third-party assessment where credibility is damaged, and provide realistic timelines the firm then meets. Repeat observations from a previous inspection are viewed especially seriously, because they indicate the quality system did not act on what it already knew.

• —Issued after agency review, not by the investigator; published on FDA’s website.
• —Typically requires a written response within 15 working days.
• —Can precede import alerts, seizure, injunction, or a consent decree.
• —May stall pending applications that list the cited facility.
• —Responses must address systemic scope — often with retrospective review and third-party assessment.
• —Repeat observations are treated as evidence the quality system failed to act.

Issued under the FD&C Act; procedures in the FDA Regulatory Procedures Manual Chapter 4 (Advisory Actions). Related actions include import alerts under §801(a), seizure under §304, and injunction under §302.