papaverine pəpăv´ərēn [key], alkaloid found in opium that acts as a muscle relaxant and vasodilator. The drug relaxes the smooth muscle of the larger blood vessels and is used to increase the blood supply to the brain or to the heart, as in the treatment of angina pectoris. It is also used in the treatment of some types of blood clot formation and in the treatment of impotence when the condition is caused by a lack of blood flow.

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