Complete Response Letter (CRL)

A Complete Response Letter (CRL) is a formal written notice the U.S. Food and Drug Administration (FDA) sends to a sponsor when it has completed its review of a New Drug Application (NDA), Biologics License Application (BLA), or an efficacy supplement, and has determined that the application will not be approved in its present form. A CRL is not an outright rejection: it identifies the specific deficiencies FDA found and gives the sponsor the option to address them and resubmit, withdraw the application, or request a hearing. The mechanism is codified at 21 CFR 314.110 (drugs) and the parallel biologics licensing regulations.

What Makes a Letter a CRL

Operationally, a communication from FDA is a Complete Response Letter (rather than an approval letter, an information request, or a refuse-to-file notice) when it meets three conditions:

• FDA has completed a full review cycle of the application, including all amendments submitted up to that point.
• The letter states the application cannot be approved in its current form and cites one or more specific grounds under 21 CFR 314.125 (grounds for refusing to approve an NDA) or 314.127 (grounds for an ANDA).
• The letter describes, at whatever level of specificity FDA provides, the deficiencies the sponsor must resolve — it is a roadmap for resubmission, not merely a denial.

What a CRL Typically Addresses

CRLs cite deficiencies in one or more of several recurring categories:

• Safety or efficacy data — the clinical evidence submitted did not adequately demonstrate the drug is safe and effective for its proposed use, additional trials or analyses are needed, or a specific safety signal requires further characterization.
• Manufacturing and Chemistry, Manufacturing, and Controls (CMC) issues — problems identified during a pre-approval inspection of the manufacturing facility, or unresolved questions about product quality, stability, or process validation.
• Labeling — disagreement over proposed prescribing information, indications, warnings, or the format of the label.
• Facility or site-level findings — deficiencies identified at a clinical investigator site or contract manufacturer during a Bioresearch Monitoring (BIMO) inspection.

A single CRL frequently cites deficiencies across more than one of these categories simultaneously.

What Happens After a CRL

A sponsor that receives a CRL has several options: submit a complete response addressing every deficiency cited (which restarts a new review clock), withdraw the application, or request a hearing on the FDA’s decision. Because a CRL is not a public refusal in the way a formal disapproval order is, sponsors historically controlled the timing and content of any public disclosure of a CRL’s existence or substance — commonly through a securities filing or press release summarizing (often only partially) the letter’s contents, since the underlying drug or biologic company is frequently publicly traded and the CRL is material information.

Public Disclosure and the openFDA CRL Database

FDA’s regulations at 21 CFR 314.430 historically restricted the agency from confirming the existence of a pending application, let alone releasing the text of a CRL, before an approval action. That has changed: FDA now operates a public Complete Response Letters database through its openFDA transparency initiative, publishing the text of CRLs (with confidential commercial information and trade secret information redacted per FDA’s disclosure regulations at 21 CFR Part 20) for NDAs and BLAs. As documented on FDA’s own transparency page, coverage is not exhaustive: FDA states it may publish batches of CRLs from its archives on an ongoing basis, and the dataset does not cover medical device applications. Sponsors and researchers relying on the database for a complete historical record should treat it as a growing, FDA-curated release rather than a comprehensive index of every CRL ever issued, and should still corroborate specific letters against a sponsor’s own public disclosures (e.g., SEC filings) where precision matters.

Worked Examples

Example 1: A sponsor submits an NDA for a new oncology therapy. During FDA’s review, a pre-approval inspection of the sponsor’s manufacturing facility identifies unresolved CMC issues with process validation. FDA issues a CRL citing the manufacturing deficiency as the sole basis for non-approval, with no concerns raised about the clinical safety or efficacy data. The sponsor resolves the manufacturing issue and resubmits; FDA’s subsequent review is limited in scope to the resubmitted material.

Example 2: A sponsor submits a BLA supported by a single pivotal trial. FDA issues a CRL stating the efficacy data from that single trial is insufficient to support approval and requesting an additional adequate and well-controlled trial. This is a substantive scientific deficiency, not a procedural or manufacturing one, and typically requires a materially longer resubmission timeline than a CMC-only CRL.

Counter-Example: Not a CRL

A refuse-to-file (RTF) letter is not a CRL. FDA issues an RTF before substantive review begins, when the application is administratively or scientifically incomplete on its face (for example, missing required studies or data). A CRL, by contrast, is only issued after FDA has completed a full review cycle of a filed, complete application. Similarly, an FDA approval letter with post-marketing requirements attached is not a CRL — the application has been approved, just with conditions, whereas a CRL means the application has not been approved at all in its current form.

Related Terms

See also Inspection Readiness for how BIMO inspection findings that can trigger a CRL are avoided at the site level.