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Characterization and metabolic profiling of oxymetholone and methasterone metabolites studied with human liver S9 model using GC-Orbitrap-HRMS for anti-doping purposes - Analytical and Bioanalytical Chemistry In vitro metabolic models provide a means to circumvent the ethical concerns associated with human administration research, allowing for preliminary predictions of human metabolism while generating high concentrations of metabolites for characterization. As S1.1-class anabolic androgenic steroids on the World Anti-Doping Agency (WADA) Prohibited List, oxymetholone and methasterone have consistently appeared in the top 20 substances identified in adverse analytical findings (AAFs) in recent years, reflecting their persistent abuse patterns in sports. Given their exogenous nature, the metabolites of these steroid hormones fall within the scope of doping control, making metabolic studies a crucial aspect of anti-doping research. In this study, human liver S9 fractions were employed as a model for the characterization and metabolic profiling of oxymetholone and methasterone via gas chromatography-orbitrap-high-resolution mass spectrometry (GC-Orbitrap-HRMS). The full scan mode of GC-Orbitrap-HRMS was utilized to detect free and two conjugated fractions of metabolites, comparing these with control groups to confirm the metabolites during in vitro incubation. Possible metabolite structures were inferred from EI mass spectra, and the metabolic pathways for both drugs were discussed. In vitro, three oxymetholone and five methasterone metabolites were identified, and among them, two metabolites, OMT-M3 (2α,17α-methyl-5ξ-androstan-3α,6β,17β-triol) and MTS-M3 (2α,17α-dimethyl-5ξ-androstane-3α,12ξ,16ξ,17β-tetrol), were characterized as novel metabolites based on recent human in vivo metabolic studies. These metabolites exhibited diverse metabolic pathways, and their structures were corroborated through complementary in vitro and in vivo metabolic analyses. This study provides a comprehensive evaluation of the applicability of the human liver S9 model in the metabolic studies of anabolic steroids in vitro, verifying novel human metabolites and providing valuable insights for future research in this field. Graphical Abstract https://link.springer.com/article/10.1007/s00216-025-06066-w