Lithium is one of the most widely used medications for the treatment of bipolar disorder (BD). It also has some side effects on thyroid functions. We aimed to investigate the role of oxidative stress, trace elements, and hemorheological parameters on the pathophysiology of thyroid dysfunctions developed by lithium treatment in patients with BD. Patients with BD were divided into three groups: patients that non-lithium-treated, lithium-treated patients for 4-6 weeks, and lithium-treated patients for 40-68 weeks. Blood samples for analysis were taken before and after the treatment period. After analysis, patients were divided into six groups: non-treatment BD group (Group 1); short-term lithium-treatment group that did not develop thyroid dysfunctions (Group 2); short-term lithium-treatment group that developed hyperthyroidism (Group 3); long-term lithium treatment group that developed hypothyroidism (Group 4), long-term lithium-treatment group that developed hyperthyroidism (Group 5), and long-term lithium-treatment group that did not develop thyroid dysfunctions (Group 6). Plasma and whole blood viscosity levels were significantly increased in Groups 4 and 6 compared to Groups 1, 2, and 3. Hemoglobin levels were lower in Group 4 than in Groups 1, 2, and 5. Fibrinogen values were higher in Groups 4 and 5 than Group 1. Plasma and erythrocyte malondialdehyde levels were higher in Group 4 than In Groups 1, 2, 3, and 5. Also, they were increased in Group 6 in comparison with Groups 2 and 3. Erythrocyte glutathione levels were lower in Groups 4 and 6 than Groups 1, 2, 3 and 5. Plasma protein carbonyls levels were higher in Group 4 than in Group 1, or in Group 5 than in Groups 1, 2, and 3, as well as in Group 6 than Groups 1, and 2. Serum zinc levels were higher in Groups 2, 3 and 6 than in Group1. Serum copper levels increased in Groups 2, 4 and 6 in comparison with Group1. The results of this study indicate that oxidative stress increased with treatment time in lithium-induced thyroid dysfunctions. Also, whole blood viscosity, plasma viscosity, fibrinogen, zinc, and copper levels were affected by lithium treatment and treatment duration induced thyroid dysfunctions.