We examined the relationship between outpatient medical costs and changes in body weight in 105 obese patients (BMI >25.0 kg/m²) with type 2 diabetes without diabetic macroangiopathies, GLP-1 receptor agonist use or SGLT2 inhibitor use for 5 years from 2008. The outpatient medical cost significantly increased in the weight-loss group (n=56), from an average of 323,000 yen/year to 369,000 yen/year as well as in the weight-gain group, from 356,000 yen/year to 473,000 yen/year. However, the change (46,000 yen/year vs. 117,000 yen/year) was significantly lower in the weight-loss group than in the weight-gain group. Furthermore, in the weight-loss group, the HbA1c value did not worsen, and the number of prescribed drugs for lifestyle-related diseases did not increase, in contrast to the weight-gain group. The change in outpatient medical cost was significantly correlated with the change in the number of drugs being administered for lifestyle-related diseases. These results suggest that non-pharmaceutical weight loss in obese patients with type 2 diabetes may suppress the increase in medical costs via an absence of deterioration in glycemic control and no increase in numbers of prescribed drugs.