narcotic analgesic alkaloid originally isolated from opium .
It is among the most powerful naturally occurring compounds in its ability to reduce pain and distress; its calming effect protects the system against exhaustion in traumatic shock , internal hemorrhage , congestive heart failure , and other debilitating conditions. Morphine is usually given by injection but may be taken by mouth. Its most serious drawback is its addictiveness; many doctors are reluctant to use amounts adequate to relieve severe pain, even though short-term use in such cases rarely leads to drug addiction . This remains controversial even in terminal cases, when addiction is arguably irrelevant; another issue in such cases is that large doses depress respiration and may thus hasten death.