PharmacovigilanceLast reviewed April 2026

Boxed Warning(Black Box Warning)

The strongest warning that FDA requires in prescription drug labeling, highlighting serious or life-threatening risks.

Usage Examples

FDA required a boxed warning for hepatotoxicity risk based on post-approval safety signals.
The labeling supplement added REMS and boxed warning for the newly-identified cardiovascular risk.

What is Black Box Warning?

A Boxed Warning — historically called a Black Box Warning — is the most prominent safety information in FDA-approved prescription drug labeling, appearing within a bold-border box at the beginning of the Prescribing Information. Boxed warnings are required when adverse reactions are so serious in proportion to the benefit that clinicians need special alerting, or when the risk can be prevented through appropriate prescribing.

Boxed warnings can be required at initial approval based on the safety profile, or added post-approval through labeling supplements when new safety information emerges (signal detection, REMS requirements, aggregate safety reviews). They often accompany REMS, medication guides, and other risk minimization measures. Sponsor-initiated or FDA-required, boxed warnings significantly affect prescribing behavior and commercial performance.

Regulatory Context

This term appears most often in pharmacovigilance workflows where submission quality, regulatory evidence, and audit readiness depend on consistent language. It is commonly referenced alongside 21 CFR 201 57, FDCA.

FDAEMAWHO

When This Matters

FDA required a boxed warning for hepatotoxicity risk based on post-approval safety signals.
The labeling supplement added REMS and boxed warning for the newly-identified cardiovascular risk.

Common Mistakes

Treating safety signal reviews as periodic instead of continuous.
Not linking new enforcement letters to internal CAPA and labeling workflows.
Using static templates for dynamic benefit-risk communication updates.

Related Regulations

21 CFR 201 57FDCA

Frequently Asked Questions

When adverse reactions are serious enough that clinicians need special alerting, when serious risks can be prevented through appropriate prescribing, or when the drug has a narrow therapeutic index requiring monitoring. FDA makes this determination based on safety profile.

Yes. Many boxed warnings are added after initial approval based on post-market safety signals, clinical trial data from ongoing studies, or epidemiologic findings. The sponsor files a labeling supplement; FDA may also require the addition under 21 USC 355(o).

Studies show boxed warnings reduce prescribing volume by 10-30% on average, though impact varies by drug class and alternative availability. Some sponsors successfully negotiate narrower warnings through strong risk-benefit arguments or REMS commitments.