This study by Rashidi and colleagues 1 sought to characterize the association of antibiotic exposure and timing of the exposure relative to allogeneic hematopoietic stem cell transplantation (allo-HCT) with the hazard of developing acute graft-vs-host disease (aGVHD), which is one of the most common complications of allo-HCT. Rashidi et al 1 applied 3 orthogonal methods (conventional Cox proportional-hazards regression, marginal structural models, and machine learning) to analyze data collected from 2023 patients who underwent their first T-replete allo-HCT at a single center between 2010 and 2021. Each of the included analytical methods has its own strengths and weaknesses, but together they provided a comprehensive perspective. Rashidi et al 1 reported that weeks 1 and 2 after allo-HCT were the highest-risk intervals, with several antibiotic exposures associated with higher risk of subsequent aGVHD. Of note, carbapenems exposure weeks 1 and 2 after allo-HCT was associated with a minimum hazard ratio (HR) of 2.75 (95% CI, 1.77-4.28), whereas week 1 after allo-HCT exposure to penicillins with β-lactamase inhibitors was associated with a minimum HR of 6.55 (95% CI,. Across all 3 methods, the data from the study by Rashidi et al 1 also suggest that pre-allo-HCT exposure to penicillins with β-lactamase inhibitors was associated with a lower risk of aGVHD.