A powerful narcotic agent with strong analgesic (painkilling) action and other significant effects on the central nervous system. It is dangerously addicting. Morphine is a naturally occurring member of a large chemical class of compounds called alkaloids. Morphine is highly effective in relieving pain. It also inhibits the cough reflex, decreases the desire to eat, and causes constipation. Side effects include impairment of mental performance, euphoria, drowsiness, lethargy, and blurred vision.

The name, which derives from Morpheus, the mythologic son of sleep and god of dreams, was coined in 1805 by German apothecary Adolf Serturner (1783-1841) to designate the main alkaloid in opium. Opium comes from the poppy plant.