An opioid analgesic drug derived from the opium poppy. Morphine is given to relieve severe pain caused by myocardial infarction, major surgery, serious injury, and cancer. Morphine blocks the transmission of pain signals at sites called opiate receptors in the brain and spinal cord. The drug also induces a sense of well-being or euphoria. Side effects include drowsiness, dizziness, constipation, nausea, vomiting, and confusion. Long-term use of morphine may lead to drug dependence, with severe flu-like symptoms when the drug is withdrawn (see withdrawal syndrome).


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