Abstract: Aims: This study aimed to determine the venetoclax (VEN) concentration in patients, analyse its correlation with adverse events (AEs), and assess the effects of combined medications on both VEN concentration and concentration-related AEs. Methods: The concentrations of VEN in 114 enrolled patients were measured. Among these patients, 52 were treated with single-agent VEN, 20 with VEN in combination with omeprazole (OPZ), 20 with VEN combined with voriconazole (VCZ), and 22 with VEN in conjunction with posaconazole (PCZ). The relevant data were subjected to statistical analysis. Results: Concentration/daily dose ratio (C/D) for the minimum (C min) and maximum (C max) concentrations of VEN were negatively correlated with white blood cell count (WBC) and neutrophil count (NEUT) but positively correlated with lactate dehydrogenase (LDH). The effect of combined medications on VEN concentration: VEN + PCZ group/VEN + VCZ group > VEN + OPZ group > VEN group. When the C max (C/D) value of VEN is 11.21, it has the highest predictive value for reducing AEs in patients with grade ≥3 NEUT. Conclusion: Increased VEN concentration increased the incidence of grade 3 or higher haematological adverse events in patients. CYP3A inhibitors significantly increased VEN levels, thereby increasing the risk of AEs.