Purpose <p>A powder found at a fatality scene, labeled as the synthetic cathinone 3’,4’-methylenedioxy-α-pyrrolidinohexiophenone (MDPHP)&#xa0;and most likely smoked using a crack pipe, was analyzed. The powder was identified as very potent synthetic cannabinoid ADB-BUTINACA/ADB-BINACA with a high purity (&gt; 98%). This case highlights the risks associated with mislabeled novel psychoactive substances (NPS), particularly those purchased online.</p> Methods <p>The powder was analyzed using liquid chromatography-high resolution mass spectrometry (LC-HRMS), liquid chromatography-tandem mass spectrometry (LC-MS/MS), and nuclear magnetic resonance (NMR) spectroscopy. Comprehensive toxicological screening, including NPS, was performed in urine and blood. ADB-BUTINACA was quantified using a standard addition method on various post-mortem matrices: femoral and heart blood, urine, stomach content, bile fluid and liver tissue. Scalp hair was analyzed via external calibration to assess potential long-term exposure.</p> Results <p>ADB-BUTINACA concentrations were 34.5 ng/mL in femoral blood, 101 ng/mL in heart blood and 3.1 ng/mL in urine. Traces of MDMB-BUTINACA were found in the powder and hair, but not in other biological matrices. ADB-BUTINACA metabolites were detected in all biological matrices. MDPHP was found at low concentrations (&lt; 2 ng/mL) in blood and urine but not in the powder, indicating prior cathinone use. A toxicological significance score (TSS) of 3 was assigned for this monointoxication with ADB-BUTINACA.</p> Conclusions <p>This case demonstrates fatal poisoning due to extremely high ADB-BUTINACA concentrations in post-mortem blood samples, emphasizing the severe risks associated with mislabeled substances. It underscores the importance of drug checking services to prevent poisonings and overdoses caused by highly potent NPS.</p>