SUMMARYRisks of food fraud have been exacerbated by ongoing supply-chain shortages and reduced regulatory oversight caused by the COVID19 pandemic. Since food fraud cases involve adulterants that are deliberately disguised, resulting poisonings are especially difficult to investigate and treat. We encountered a near-fatal poisoning with “weight-loss candlenuts” that are readily available online. We leveraged state-of-the-art high-resolution mass spectrometry (HRMS) and discovered that commonly used spectral libraries and toxin/poison standards panels do not contain the materials needed to identify the causative agents of this nearly lethal poisoning. By building new methods, we ultimately found ‘Nuez de la India’ contain high levels of uncommon cardiac glycosides, while deploying HRMS as a novel ‘chemical fingerprinting’ tool revealed them to be mislabeled yellow oleander seeds. Our work presents a rapid investigative strategy to empower future investigations, and provides guiding principles to food safety programs for treating, and indeed preventing, these potentially fatal poisonings that are increasing worldwide.