efficacy of levothyroxine on benign thyroid nodule

background: suppressive therapy with levothyroxine for reducing the size of thyroid nodules has not been really accepted. the purpose of this study was to assess the effect of levothyroxine on the size of benign thyroid nodules. methods: forty patients with confirmed benign nodule were randomly divided into two groups. group i received 50?g/day levothyroxin for six months but group ii did not take it. sonography was used to measure the dimensions of nodules before and after six months. tsh serum levels were measured before and after treatment. this clinical trial study was registered as irct 201103185692 n3. the data were collected and analyzed. results: the mean age of levothyroxine group was 41.57±9.41 and control group was 44.45±10.9 years (p=0.386). the tsh levels and longitudinal and transverse dimensions in both groups were similar (p>0.05). the tsh levels before and after treatment were 2±1.65 and 0.52±0.67 mui/l (p=0.001). the longitudinal and transverse dimensions before and after treatment in case group were 1.9±1.11, 1.90±1.15 and 1.44±0.90, 1.49±1.02 cm respectively (p=0.74, p=0.7, respectively) but in control group, were 2.19±1.32, 1.97±1.4 and 1.57±0.95, 1.26±0.7, respectively (p=0.35 and 0.1, respectively). conclusion: the results show that suppressive therapy with levothyroxine lead no alteration in the size of benign nodules.