BACKGROUND: We aimed to examine how oxidative stress changes after treatment and its relationship with metabolic parameters in patients diagnosed with Type 2 Diabetes Mellitus treated with metformin alone or with a combination of metformin and pioglitazone. METHODS: The study population consisted of a total of 60 patients, including the group diagnosed with Type 2 Diabetes Mellitus (T2DM) who received metformin 2x1000 mg (n=30) and the other group who received metformin with pioglitazone 2x15/1000 mg (n=30). Serum IMA (ischemia-modified albumin), TAS (total antioxidant status), TOS (total oxidant status) and thiol-disulphide homeostasis were measured before and after 12 weeks of treatment. RESULTS: No significant change was detected in Native sulfhydryl (SH) and Total SH levels in both Metformin and combination groups. IMA levels increased significantly in both drug groups (p=0.03 and p=0.01, respectively). Although the TAS level increased in both groups, no significant change was detected. While the TOS and oxidative stress index (OSI) index decreased significantly in the combination group (p<
0.002), the decrease in the metformin group was not significant. No significant difference was detected between Native SH, Total SH, Disulfide, IMA, TAS, TOS levels and OSI index changes of both drug groups. CONCLUSIONS: We found that the use of anti-diabetic drugs did not have a significant effect on oxidative stress.