Fentanyl in forensic autopsies: Trends, circumstances, and toxicological findings.

BACKGROUND: Postmortem fentanyl detection in medicolegal autopsy cases presents a fundamental interpretive challenge: detection does not inherently indicate non-medical use or causal involvement in death. Systematic frameworks for contextualizing fentanyl findings remain underutilized in forensic practice, particularly in settings with limited antemortem documentation. METHODS: All medicolegal autopsy cases with postmortem fentanyl detection between January 2019 and December 2024 at a high-volume metropolitan forensic autopsy institution were retrospectively analyzed. A structured three-tier exposure context classification (consistent with therapeutic indication, non-medical use, or indeterminate) was applied using routinely available autopsy variables including co-detected substances, clinical intervention markers, incident type, and external examination findings. RESULTS: Among 842 fentanyl-positive cases, 731 (86.8%) were classified as consistent with therapeutic indication, 68 (8.1%) as non-medical use, and 43 (5.1%) as indeterminate. Annual case numbers increased 87.3% over the study period. Cases meeting combined classical forensic criteria showed 90.5% non-medical classification. Non-medical decedents were markedly younger (mean 32.4 vs. 45.0 years) and more predominantly male (82.4% vs. 76.3%). Amphetamine-type stimulants predominated among co-detected illicit substances; opioid-on-opioid co-detection was rare. Tattoo presence and self-inflicted scarring were significantly more frequent in the non-medical group (p < 0.001). CONCLUSION: A structured, variable-based classification framework can meaningfully stratify postmortem fentanyl cases by exposure context using routinely available autopsy data. Systematic contextual assessment should be a standard component of medicolegal fentanyl investigation across diverse forensic settings.