Experimental diabetes models induced by streptozotocin (STZ) and alloxan are widely used in preclinical research; however, direct standardized comparisons in female rodents remain limited. The present study evaluated multiple chemical induction protocols in female Wistar rats, including STZ (40 and 65 mg/kg), STZ at the same doses combined with nicotinamide (110 mg/kg), and alloxan (130 mg/kg). Glycemic progression, oral glucose tolerance test, body weight evolution, oxidative stress markers, and multi-organ histopathology were assessed over a 14-day period. High-dose STZ (65 mg/kg) and alloxan produced rapid, sustained hyperglycemia (p < 0.0001), significant body weight reduction, increased lipid peroxidation (elevated MDA), nitric oxide overproduction, thiol depletion, and pronounced pancreatic and renal structural damage. In contrast, STZ–nicotinamide protocols generated moderate but stable hyperglycemia with partial preservation of islet architecture, attenuated oxidative imbalance, and improved systemic tolerability. Oral glucose tolerance test confirmed impaired glucose handling in the STZ–nicotinamide group, consistent with a type 2 diabetes-like phenotype rather than complete insulin deficiency. These results demonstrate that induction strategy critically determines metabolic stability, oxidative stress burden, and tissue remodeling patterns, supporting model selection according to specific experimental objectives.