Lowering of serum total T3 during a conventional slimming regime.

Serum concentrations of total triiodothyronine (T3) and thyroxine (T4) were determined in 28 obese out-patients before and after 12 weeks of treatment with a conventional slimming diet of 5.2 MJ (1245 kcal). Twenty-one of the patients were also given central stimulating anorectics (diethylpropion and 'Elsinore-pill' containing ephedrine). The median weight loss was 8.1 kg (range 0.4-19.1 kg). After the treatment a small, but significant (P less than 0.02), fall in serum T3 could be demonstrated whilst serum T4 was unaffected. The median fall in T3 in percentage of pretreatment value was 9 per cent (96 per cent confidence limits: 4-16 per cent). Neither serum T3 nor serum T4 correlated with the initial body weight, overweight or energy intake. In the patients treated with anorectics serum T4 was not elevated after 12 weeks, indicating that a possible sympatomimetic effect of central stimulating anorectics upon the thyroid gland is only temporary.