Antitussive drugs. I. Cardiopulmonary effects of codeine

In the anesthetized dog, codeine causes a combination of pulmonary vasoconstriction and systemic vasodilation. Pulmonary blood flow is either increased or decreased, relating to a primary stimulation or depression of myocardial contractility. The overall effect is an elevation in pulmonary arterial pressure largely due to vasoconstriction of the pulmonary blood vessels.