Somewhere between 25 and 60 percent of deviations and quality incidents in pharmaceutical manufacturing get attributed to human error. That figure alone should raise a question, not settle one. If human error were genuinely the dominant cause of failure at this scale, it would suggest a workforce fundamentally unable to follow procedure. In practice, it usually suggests something else: an investigation that stopped as soon as it found a plausible person to blame, rather than continuing until it found the actual systemic gap underneath.
FDA has been consistent on this point for years, and 2025 warning letters show the agency is still finding the same pattern. "Human error" as a standalone conclusion, without evidence ruling out procedural, training, equipment, or system-level causes, does not satisfy the investigation requirement under 21 CFR 211.192.
What the regulation actually requires
Section 211.192 requires a thorough investigation into any unexplained discrepancy or batch failure, whether or not the batch has already shipped. It does not name human error as an acceptable category of finding. What it requires is evidence: data supporting whatever root cause is assigned, and a scope broad enough to catch every batch potentially affected by the same failure.
Where human error is suspected or identified as the cause, this should be justified having taken care to ensure that process, procedural or system based errors or problems have not been overlooked.
Paraphrased from EU GMP guidance on deviation investigation principlesThat's the standard in plain terms: human error is a conclusion of last resort, reached only after every systemic alternative has been genuinely ruled out and documented, not a default explanation reached for because it's the fastest one available.
What this looks like when it goes wrong
Three separate 2025 warning letters illustrate the same underlying failure pattern, each at a different company.
Catalent Indiana, November 2025. FDA found that investigations into drug product failures and discrepancies lacked data supporting the assigned root causes, were not expanded to cover all potentially affected products, and were not adequately documented in the firm's deviation system. In several cases, the investigation concluded no product was impacted simply because final release testing passed, without addressing why the discrepancy occurred in the first place.
Exela Pharma Sciences, July 2025. The firm invalidated failing growth promotion test results, results used to confirm that sterility testing media actually works, without an adequate root cause investigation behind the invalidation. A test failing and then being dismissed without documented justification is exactly the kind of shortcut 211.192 exists to prevent.
Chem Tech Ltd, February 2025. An out-of-specification assay result was attributed to a separation issue as root cause, with no supporting investigation data, while the batch had also exceeded an established hold time that was never factored into the analysis. The product was reworked and released regardless.
None of these letters used the words "human error" as the final citation. What they share is the same underlying gap: a root cause assigned without the evidence to support it, and a scope too narrow to catch what else it might have affected.
In each case, the failure wasn't that a mistake happened. Mistakes happen in every manufacturing environment. The failure was stopping the investigation at the first plausible explanation instead of continuing until the evidence either confirmed it or pointed somewhere else.
What a defensible investigation actually rules out first
Before human error can be documented as a justified conclusion, a defensible investigation should be able to show it considered, and reasonably excluded, each of the following:
- Was the procedure itself clear, current, and achievable as written, or did it require a judgment call the SOP never addressed?
- Was the person involved trained and qualified on this specific task, with documentation to prove it, not just a general training record?
- Was equipment functioning within calibration and maintenance schedules at the time of the event?
- Were environmental or workload conditions, staffing levels, shift timing, competing priorities, a contributing factor?
- Has this same "human error" conclusion shown up before, on this line or with this task? A repeat finding is itself evidence of a systemic cause, not a coincidence of multiple individuals making the same mistake.
That last point is often the one investigations miss entirely. A single human error, once, with a clean investigation behind it, is plausible. The same error recurring across different shifts, different operators, or different batches is not a personnel problem. It's a system asking to be fixed.
QA investigators, production supervisors, CAPA owners, and anyone responsible for signing off on a deviation's root cause before it closes.
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GMPify's CAPA and deviation management training covers root cause methodology, documentation standards, and what a defensible investigation file actually contains.