Background:Subclinical hypothyroidism (SCH) is associated with dyslipidemia, increasing the risk of cardiovascular diseases. Thyroid hormone replacement therapy (THRT) is commonly employed to restore euthyroidism, but its effect on lipid profiles in SCH patients remains under investigation. This study aimed to evaluate the impact of THRT on lipid profiles in patients with SCH. Materials and Methods:A randomized controlled trial was conducted with 100 SCH patients, aged 18–65 years, who were divided into two groups: treatment (n=50) and control (n=50). The treatment group received levothyroxine to maintain thyroid-stimulating hormone (TSH) levels within the normal range, while the control group was given a placebo. Lipid profiles, including total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), and triglycerides (TG), were measured at baseline and after 12 weeks. Statistical analysis was performed using paired t-tests and ANOVA. Results:At baseline, lipid parameters were similar in both groups. After 12 weeks, the treatment group showed significant reductions in TC (from 210 ± 15 mg/dL to 180 ± 10 mg/dL, p<0.01), LDL (from 130 ± 12 mg/dL to 100 ± 8 mg/dL, p<0.01), and TG (from 160 ± 14 mg/dL to 140 ± 12 mg/dL, p<0.05). No significant changes were observed in HDL levels or in the control group. The placebo group exhibited no significant alterations in any lipid parameters. Conclusion:Thyroid hormone replacement therapy significantly improves lipid profiles, particularly by reducing total cholesterol, LDL, and triglyceride levels in patients with subclinical hypothyroidism. These findings support the use of THRT for cardiovascular risk mitigation in SCH patients.