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What Thyroxine Dose Is Optimal for Patients with Hypothyroidism?

Cognition and quality of life were not improved by suppressing TSH to low-normal levels.

Although the traditional normal reference range for thyroid-stimulating hormone (TSH) is 0.5 mU/L to 5.0 mU/L, some experts believe that the upper limit of normal should be lowered to about 3.0 mU/L. In addition, some clinicians believe that patients with primary hypothyroidism feel better when thyroxine (T₄) doses are adjusted to push TSH levels into the lower end of the normal range. This opinion was investigated in a double-blind randomized crossover trial involving 56 Australian patients with primary hypothyroidism. At baseline, all patients were taking stable doses of thyroxine and had TSH levels between 0.1 mU/L and 4.8 mU/L.

Through a complex scheme that involved placebos and individualized adjustments in thyroxine dosing, each patient received three randomly ordered 8-week courses of high-, medium-, and low-dose thyroxine, designed to achieve target TSH levels of <0.3 mU/L, 0.3–1.99 mU/L, and 2.0–4.8 mU/L, respectively. Extensive assessment of cognitive function, quality of life, and thyroid symptoms at the end of each 8-week treatment course revealed no differences between groups, whether analyzed by dose (high, medium, or low) or by TSH level actually attained (<0.3 mU/L, 0.3–1.99 mU/L, or 2.0–4.8 mU/L).

Comment: These results cast doubt on the idea that patients with primary hypothyroidism feel better or have better cognitive performance when thyroxine doses are adjusted to achieve TSH levels near the lower limit of normal (instead of simply within the normal range).

— Allan S. Brett, MD

Published in Journal Watch General Medicine August 3, 2006

Citation(s):

Walsh JP et al. Small changes in thyroxine dosage do not produce measurable changes in hypothyroid symptoms, well-being, or quality of life: Results of a double-blind, randomized clinical trial. J Clin Endocrinol Metab 2006 Jul; 91:2624-30.

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