FDA Warning Letters to Investigators: Tutorial Examples

FDA warning letters are most often associated with manufacturing or product-related issues, but they can also be issued directly to clinical investigators when significant regulatory concerns are identified during inspections. 

These letters are typically issued months after the underlying events, following:

• an on-site inspection,

• documented observations,

• and review of written responses provided by the investigator or site.

As a result, a warning letter may appear long after the clinical activity in question has already concluded.

Here are 2 examples from December 2025:

• Example 1  - https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/purushothaman-damodara-kumaran-md-721325-12222025
• Example 2 - https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/warning-letters/devalingam-mahalingam-md-phd-721145-12112025

What such letters generally indicate

When issued to investigators, warning letters usually relate to:

• failure to conduct a study according to the investigational plan,

• inadequate oversight of delegated study activities,

• deficiencies in subject protection or regulatory compliance,

• or concerns about data integrity.

They do not imply intent or misconduct by default. Rather, they reflect the FDA’s assessment that regulatory requirements were not sufficiently met and that prior responses were inadequate to address the identified concerns.

Why this matters for education and training

For students and professionals in clinical research, warning letters serve as regulatory learning artifacts. They illustrate:

• how oversight responsibilities are interpreted,

• how delegation does not remove accountability,

• and how regulatory timelines often extend well beyond study execution.

Importantly, warning letters focus on systems and controls, not only on isolated errors.

A broader takeaway

The existence of investigator-directed warning letters highlights the importance of:

• clear role definition,

• active oversight models,

• and quality systems that remain effective even under operational pressure.

Understanding that such letters can be issued — and why — is often more valuable educationally than analyzing individual cases.

References

• U.S. Food and Drug Administration
  FDA Warning Letters
  Official repository of all FDA warning letters across regulatory domains.
  https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/compliance-actions-and-activities/warning-letters

• U.S. Food and Drug Administration Compliance Actions and Activities High-level explanation of FDA’s enforcement tools, including warning letters, injunctions, and recalls. https://www.fda.gov/inspections-compliance-enforcement-and-criminal-investigations/compliance-actions-and-activities

• In addition to official FDA publications, industry commentary platforms such as FDA Insider provide contextual discussion of regulatory developments. The FDA Group. FDA Insider: Regulatory insights and commentary. https://insider.thefdagroup.com/ , https://substack.com/inbox/post/182104525

• Regulatory Affairs Professionals Society https://www.raps.org/news-and-articles

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This post is intended solely for educational purposes and does not comment on any specific investigation, individual, or outcome.