Glutathione (GSH) levels are modulated in human liver slices to evaluate if drug induced liver injury is enhanced by a poor liver GSH status. Liver slice GSH levels were decreased by: 1) BSO (L-buthionine-S-sulfoximine) to inhibit GSH synthesis, and by 2) APAP (acetaminophen) which consumes GSH via conjugation to a metabolite. In this study, methimazole (MMI) liver injury was evaluated in the presence of a poor GSH status. MMI was selected because its structural thione moiety is linked with hepatotoxicity and during metabolism GSH is co-oxidized. MMI (500-1000 µM) affected oxidative stress pathways and mitochondrial function, resulting in lower liver slice GSH and ATP levels. Co-incubation of MMI with BSO or APAP led to further decreases of GSH and ATP levels in some human livers, at time points and concentrations not detected with MMI alone. Variation in human response was evident and demonstrated that some subjects with a poor liver GSH status could be further compromised with high MMI concentrations. MMI induced an up-regulation of gene expression linked with the GSH pathway, mitochondrial GSH and inflammation. Co-treatment of MMI with BSO induced a mixed response of oxidative stress related genes and an up-regulation of heat shock genes. The combination of MMI with APAP increased the expression of genes involved with oxidative stress and anti-oxidant defense, likely to protect the cells from mitochondrial injury. In summary, MMI induces oxidative stress at high concentrations, which can be augmented when liver GSH levels are decreased by the co-administration of some drugs or health status.