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Constipation: A common side effect of opioid use

Written by: Kevin Zacharoff, MD
Published: Tuesday, March 09, 2010
Reviewed by: Evelyn Corsini, MSW, March 2010

Constipation: A common side effect of opioid use

Many people who live with chronic pain try taking over-the-counter pain relievers or use non-drug methods (like behavioral or physical therapy) to feel better. In some cases, though, these methods may not be enough. That’s when a pain specialist may prescribe an opioid pain reliever instead, like oxycodone or fentanyl. While these medications work well, they all have constipation as a common side effect.

What causes constipation?

As food moves through the large intestine, it absorbs water from the food and forms waste products, or stool. By the time stool reaches the rectum it is fairly solid, because most of the water has been absorbed. If the large intestine absorbs too much water, or if the colon’s muscle contractions are slow or sluggish, constipation can develop. This is a situation where the stool becomes very hard and difficult to pass, or there are irregular, infrequent bowel movements. Constipation is usually defined as being three or fewer bowel movements during a week; it can add extra pain and suffering to the discomfort that a person with chronic pain is already feeling. 

Why is constipation a side effect of opioids?

Constipation is one of the most common side effects of opioid therapy, but it’s actually a normal response on the part of your body. Opioid use slows down muscle contractions and movement in the stomach and intestines; it causes sluggishness in passing waste and allows for more water than normal to be absorbed in the intestines. This makes stool hard, dry, and more difficult to pass.

Many other medications can also cause constipation, including:

• Antacids that contain aluminum and calcium
• Some blood pressure medications (calcium channel blockers)
• Anti-Parkinson drugs
• Antispasmodics
• Antidepressants
• Iron supplements
• Diuretics (water pills)
• Anticonvulsants

How is constipation treated?

Persistent constipation is so uncomfortable that it’s a major reason why patients often don’t take their pain medicines as directed.

If you’re dealing with opioid-related constipation, tell your health care provider – especially if you’ve gone through it before or you’re prone to the problem. Most often, health care providers will tell their patients to drink plenty of fluids in order to keep their stool soft. In addition, the provider may suggest taking laxatives (senna or bisacodyl) or stool softeners (milk of magnesia or docusate sodium). Though stool softeners may help with constipation, (making it easier to pass stool and have a normal bowel movement), they may not be enough to get rid of all the symptoms. That’s why a stimulant laxative may be needed, to urge the bowel to move the stool along and fight the sluggishness. Most laxatives are available without a prescription, but it’s always best to get advice and recommendations from your doctor and pharmacist about the proper use of this medicine.

It’s crucial to prevent and treat opioid-related constipation early: Constipation can sometimes lead to complications, and it can get worse if it’s ignored. If constipation becomes a problem for you, let your health care provider know. Your treatment plan may need to be changed, by decreasing the dose of the opioid, switching to a different opioid, or changing the way that the opioid is given.


National Digestive Disease Information Clearinghouse-National Institute of Diabetes and Digestive and Kidney Diseases, NIH. Constipation. Accessed on December 14, 2009 at