An alkaloid found in opium but not closely related to the other opium alkaloids in its structure or pharmacological actions. Papaverine is a vasodilating agent. Papaverine is used for the treating certain conditions that are accompanied by smooth muscle spasms (eg, blood vessel, urinary, gallbladder, or intestinal spasm). Papaverine is a nonxanthine phosphodiesterase inhibitor for the relief of cerebral and peripheral ischemia associated with arterial spasm and myocardial ischemia complicated by arrhythmias. The main actions of Papaverine are exerted on cardiac and smooth muscle. Like qathidine, Papaverine acts directly on the heart muscle to depress conduction and prolong the refractory period. Papaverine relaxes various smooth muscles. This relaxation may be prominent if spasm exists. The muscle cell is not paralyzed by Papaverine and still responds to drugs and other stimuli causing contraction. The antispasmodic effect is a direct one, and unrelated to muscle innervation. Papaverine is practically devoid of effects on the central nervous system. Papaverine relaxes the smooth musculature of the larger blood vessels, especially coronary, systemic peripheral, and pulmonary arteries. Papaverine is a potent, specific inhibitor of PDE10A. Papaverine for treatment of erectile dysfunction (ED) is excluded from coverage.