['In patients with primary hypothyroidism, anecdotal evidence suggests that well-being is optimized by fine adjustment of T(4) dosage, aiming for a serum TSH concentration in the lower reference range. This has not been tested in a clinical trial.', 'Our objective was to test whether adjustment of T(4) dosage aiming for a serum TSH concentration less than 2 mU/liter improves well-being compared with a serum TSH concentration in the upper reference range.', 'We conducted a double-blind, randomized clinical trial with a crossover design.', 'Fifty-six subjects (52 females) with primary hypothyroidism taking T(4) (>/=100 microg/d) with baseline serum TSH 0.1-4.8 mU/liter participated.', 'Each subject received three T(4) doses (low, middle, and high in 25-microg increments) in random order.', 'Outcome measures included visual analog scales assessing well-being (the primary endpoint) and hypothyroid symptoms, quality of life instruments (General Health Questionnaire 28, Short Form 36, and Thyroid Symptom Questionnaire), cognitive function tests, and treatment preference.', 'Mean (+/- sem) serum TSH concentrations were 2.8 +/- 0.4, 1.0 +/- 0.2, and 0.3 +/- 0.1 mU/liter for the three treatments. There were no significant treatment effects on any of the instruments assessing well-being, symptoms, quality of life, or cognitive function and no significant treatment preference.'] Do small changes in thyroxine dosage produce measurable changes in hypothyroid symptoms , well-being , or quality of life : results of a double-blind , randomized clinical trial?