Here we contrast the vascular smooth muscle contractility produced by D-nor-pseudoephedrine, alone or combined with triiodothyronine, on the aorta and coronary vasculature of the rat. At high concentrations (greater than those found in normal therapeutic dosing) D-nor-pseudoephedrine contracted the aorta. In contrast, it produced vasodilation on pre-contracted aorta independently of the vasoconstrictor employed or the presence of vascular endothelium. D-nor-pseudoephedrine increased coronary perfusion pressure, but the effect was smaller than the vasoconstriction produced by phenylephrine (a full alpha 1 adrenergic agonist), and was blocked by the pre-treatment with triiodothyronine. These results suggest cardiovascular risks in the use of D-nor-pseudoephedrine for weight loss.