Fatal oral ingestion of a sectioned transdermal fentanyl patch in an opioid-naïve youth with gender incongruence: a forensic case report from Japan

BACKGROUND: Fentanyl is a central driver of the global opioid crisis due to its extreme potency and abuse liability. Japan has historically maintained a low prevalence of opioid use disorders; however, the diversion of prescription pharmaceuticals has emerged as a discrete threat, particularly among adolescents and young adults. Herein, we report a fatal case of acute intoxication caused by the deliberate oral misuse of a transdermal fentanyl patch. CASE PRESENTATION: An adolescent (late teens) with a history of depression and gender incongruence died at home. The deceased had no history of chronic pain and was not prescribed opioids. A forensic autopsy revealed five sectioned fragments of a transdermal fentanyl patch in the gastric contents. Toxicological analysis using liquid chromatography-tandem mass spectrometry yielded fentanyl concentrations of 23.4 and 23.0 ng/mL in peripheral blood and heart serum, with corresponding norfentanyl concentrations of 9.5 and 12.1 ng/mL, respectively. Pregabalin was concurrently detected at a high therapeutic concentration (3.8 μg/mL in peripheral blood; 7.0 μg/mL in heart serum). CONCLUSION: The sectioned patch fragments identified in the gastric contents, in conjunction with the overall toxicological findings, supports acute death attributable to oral patch abuse. However, inverted fentanyl-to-norfentanyl ratio (>1.0) was interpreted cautiously, acknowledging that post-mortem redistribution cannot be excluded. The opioid-naïve status of the deceased and concomitant central nervous system depressant effects of pregabalin and co-detected benzodiazepine-related exposure probably contributed to these outcomes. This case highlights the risks associated with high-potency opioid diversion and abusive routes of administration in psychologically vulnerable young people.