BOTH clofibrate and dextrothyroxine have been shown to reduce the serum levels of cholesterol1,2 and triglycerides 3-5 in man. The clinical significance of these lipid-lowering effects and other possible long-term effects of the compounds remain incompletely understood. The relative importance of the levels of cholesterol as compared to those of triglycerides remains unclear since data from adequate prospective studies are limited in regard to triglycerides.
The mode of action of the two compounds appears to be quite different. Dextrothyroxine is thought to act mainly by increasing the conversion of cholesterol to bile acids and thus hasten its excretion6; clofibrate has been shown in the rat to reduce net triglyceride output from the liver 7 and also to decrease the rate of cholesterol synthesis in the liver.8 It is thus not surprising that their effects differ. We suggested that both compounds effect a reduction in serum cholesterol but that clofibrate had