Morphine is a narcotic medication used to treat severe pain. This medicine causes several gastrointestinal side effects, most related to the drug’s slowing effect on the activity of the stomach and intestines. Changes in dose or route of administration and co-administration of other medications can help control the unwanted gastrointestinal side effects of morphine.
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Dry Mouth and Taste Alteration
Morphine commonly causes a dry mouth, also known as xerostomia. In a 2006 study on the adverse effects of morphine published in “The American Journal of Hospice and Palliative Medicine,” Dr. Paul Glare and his colleagues found dry mouth was the most commonly reported side effect of chronic morphine therapy. Dry mouth can cause changes in the sense of taste, which may adversely affect appetite.
Morphine slows the normal muscular activity of the stomach, which leads to delayed gastric emptying after eating. This side effect can cause a prolonged sense of fullness after eating and may cause a vague sense of stomach discomfort. Some people on morphine also experience heartburn due to stomach acid refluxing into the esophagus (the tube that carries food to the stomach).
Decreased appetite may occur while taking morphine. Delayed gastric emptying and slow movement of food through the intestines may contribute to this side effect.
Nausea and Vomiting
Morphine can stimulate the nausea trigger centers in the brain; nausea may occur with or without vomiting. This side effect is typically more pronounced in people who are ambulatory than in those who are bedridden. Co-administration of medication to control nausea is helpful for some people that experience this distressing side effect.
Morphine can cause spasms of the gallbladder and bile duct. The spasms typically cause abdominal pain in the area between the belly button and the lower end of the breastbone. Abdominal pain may also occur if the bowel becomes obstructed as a complication of morphine therapy; the pain is typically intense and crampy.
Abdominal Fullness and Constipation
Morphine markedly slows the propulsive muscular activity of the intestines. Thus, food moves through the intestines at a much slower pace than normal. This often causes an uncomfortable sense of abdominal fullness and frequently leads to constipation. When digested material enters the large intestine, it usually contains a large amount of water. The slowed movement through the colon causes an excessive amount of water to be absorbed from the fecal matter. The stool becomes large, firm, and difficult to pass. The situation is further aggravated by a dampened defecation response--the body does not respond as quickly, as it normally would to the presence of stool in the rectum. Stool softeners, laxatives, fiber and hydration are often used to counter this common side effect of morphine. In 2010, Dr. Ashok Tuteja and his fellow researchers reported results of a study on opioid-induced bowel disorders published in the journal “Neurogastroenterology and Motility” finding nearly 47 percent of people on chronic morphine therapy experience constipation.