Objective: Levothyroxine (LT4) is used by almost 13 million patients in USA and in the same country it has been estimated that 35% of subjects are obese. Oral thyroxine has a narrow therapeutic index and the dose must be tailored on the patient to avoid the over- or under-treatment and the related side effects. Studies on this subject were mostly carried out in thyroidectomized patients and/or in non standardized treatment schedule. Our study was aimed at investigating LT4 daily requirement in overweight or obese patients taking T4 in a tightly controlled fashion. Methods: Upon the exclusion of patients non-compliant and/or using drugs and/or with diagnosed gastrointestinal disorders, 60 overweight/obese hypothyroid patients with Hashimoto’s thyroiditis (55 F/5 M; median age = 44 ys) represented the study group. They were subdivided in: 26 overweight (O), 17 class I obese (C-I), 10 class II obese (C-II), 7 class III obese (C-III). Thirtyfive (34 F/1 M; median age = 40 ys) age-matched patients with normal BMI (35 kg/m2; n = 17) (–12%; p = 0.023). Conclusion: Daily T4 requirement is similar in normal and overweight patients while all classes of obese patients show a progressively reduced need for T4 requirement
