The efficacy of thyroid hormone therapy of hypothyroidism has been known for over 100 years. Thyroxine (L-T4) monotherapy is the current preferred chronic therapy. Use of thyroid gland extract was the standard until synthetic thyroxine became readily available, but current use is controversial.  Liothyronine (L-T3) is conventionally used short-term, during thyroid hormone withdrawal preparation for whole body radioiodine scanning in thyroid cancer assessment, in treatment of myxoedema coma, and chronically in rare patients apparently intolerant or unresponsive to oral thyroxine. Thyroxine has a proven role in the treatment of overt primary hypothyroidism and secondary (central) hypothyroidism. In subclinical hypothyroidism (mild thyroid failure) thyroid hormone is appropriate in some but not all cases¹. TSH-suppressive therapy with thyroxine is a component of chronic treatment of differentiated thyroid carcinoma. Thyroxine therapy to attempt shrinkage of sporadic multinodular goitre is generally contra-indicated because exogenous thyroxine therapy can induce hyperthyroidism with increased risk of cardiac arrhythmia and acceleration of bone loss with increased risk of osteoporotic fracture². Occasionally TSH is raised with an apparent multinodular goitre and in this situation thyroxine therapy is indicated³. The effect of thyroxine to reduce thyroid nodule size is variable and modest⁴. Other uses can be classified as misuse, abuse, or use where the evidence of efficacy and safety is insufficient by acceptable scientific standards. These include use of animal thyroid gland extract, or use of combination T4 and T3 therapy⁵, in preference to T4, as usual replacement therapy in hypothyroidism, use of thyroid hormone in biochemically euthyroid patients where symptoms are held to be those of hypothyroidism including so-called “Wilson’s syndrome’^{6, 7} , use to promote weight loss (especially of T3)⁸, use to improve treatment response in depression⁹, and use in non-thyroidal illness including cardiac transplant donors and recipients¹⁰ . Thyrotoxicosis factitia is straightforward abuse by personal not iatrogenic initiative.