Mitochondria are central organelles of cellular energy metabolism, producing the majority of intracellular ATP, and glutamine serves as a key carbon source, fueling the TCA cycle and various other metabolic pathways to support energy production and biosynthetic reactions. In this study, HepG2 cells were treated with drugs that induce mitochondrial damage, including chlorpromazine (CLP), benzbromarone (BBR), and clozapine (CZP) at different concentrations to determine the onset of cellular damage. Based on these concentrations, [U-¹³C₅]-glutamine tracing was performed to compare drug-specific alterations in glutamine metabolism. The results showed that CLP and CZP activated the reductive carboxylation (RC) pathway from α-ketoglutarate to citrate in a concentration-dependent manner, whereas BBR suppressed the RC pathway toward citrate and enhanced the oxidative TCA pathway toward aspartate. These findings indicate that CLP and CZP suppressed the oxidative TCA pathway and consequently induced RC activation in response to oxidative TCA inhibition, whereas BBR enhanced oxidative metabolism. Overall, these results demonstrate that mitochondrial damage regulates glutamine metabolism in distinct ways depending on the underlying mechanism of injury, providing fundamental insights into the mechanisms of drug-induced mitochondrial toxicity and cellular metabolic adaptation.