Administration of sympathomimetic agents and thyroid hormone to patients with coronary artery disease may increase the risk of coronary insufficiency. Since thyroid hormones increase the catabolism of vitamin K– dependent clotting factors, the effects of coumarin anti-coagulants may be enhanced. During concomitant ther-apy, the dosage of the anticoagulant may have to be re-duced. Conversely, initiation of thyroid hormone therapy in patients with diabetes mellitus may increase the requirement for insulin or oral hypoglycemic agents. Similarly, a larger dose of cardiac glycosides (e.g., digitoxin, digoxin) may be required in digitalized patients.