Why do opioids make you constipated?

Neil Chatterjee, MD headshot

Medically reviewed by Neil Chatterjee, MD

How it works

Opioids work on several receptors at the cell level, located in the central nervous system and the gut. Opioids, when attached to these receptors in the brain and spinal cord, block pain. However, there are also opioid receptors throughout the gastrointestinal tract, including mu, delta, and kappa opioid receptors. Opioid medications target the mu receptors in your GI tract, which can slow down food passing through the gut. This increases water absorption, which often makes stool overly hard and dry. Similarly, opioids may decrease the intestine's ability to contract ("peristalsis") or cause it to contract in odd ways.

Treating Opioid-Induced Constipation (OIC)

Constipation is a common side effect of opioid analgesics and can cause significant discomfort even when taking the medication just for a couple of days. OIC is often challenging to treat and may require a combination of nonpharmacologic (i.e. behavioral) and pharmacologic options.

The type, frequency, and chronicity of symptoms often dictate which drug is best for you. Pregnancy, breast feeding, certain chronic diagnosis, and age all are important considerations before treating OIC. Prevention planning should be discussed and initiated with your prescriber before starting any opioids.

Behavioral Options  

Increase water intake

Opioids stimulate the absorption of fluids, and increasing fluid intake alone can often rectify the discomfort of constipation. Drinking warm water with lemon frequently can induce a softer and more regular bowel movement.

Stay active

Exercise improves blood flow to the gastrointestinal organs, resulting in more muscular contractions of the intestines. Increasing heart rate stimulates muscles in the intestine, which assists in more improved bowel movements. Muscles in the abdominal wall and the diaphragm play a vital role in this process and exercise assists in the contraction of these muscles.

Increase fiber intake

Fiber significantly improves the quality of a bowel movement by adding bulk and weight to the stools. This softens the consistency, which, in turn, stimulates bowel movements. On average, most people consume approximately five to ten grams of fiber a day, whereas the recommended intake is 20-35 grams daily. Some people experience increased bloating and excessive gas when increasing fiber too quickly.  

Position and timing 

In order to assist in the process of defecation, posture plays an important role

  • Position your knees higher than your hips
  • Try to make sure your spine is relatively straight and lean forward
  • Attempt to go to the bathroom after exercise or 30 minutes after a meal
  • Never ignore the urge to go

Over-the-counter options

Fiber enhancing drugs

Fiber mixtures added to liquid can assist in maintaining a regular bowel movement. It is always important to start slow and never introduce too much.

Gastrointestinal stimulant medications

These can assist the process of evacuation by enhancing the contraction of specific GI muscles. Common drugs include, Bisacodyl (Dulcolax) and sennosides (Senokot,Ex-lax).

Stool softeners 

These drugs do exactly what their name implies--they improve the consistency of the stool by softening it. A common drug in this category is docusate (Colace).

Osmotic laxatives

These drugs assist the stool in traveling through to the colon, enhancing the stimulation of bowel movements. Examples include Milk of Magnesia and Miralax.


Bowel movement enhancement by softening the stool consistency using water enemas through stimulation.

Prescribed options

Drugs that affect fluid in the intestines

These include plecanatide (Trulance) and linaclotide (Linzess). These drugs are only approved for adults.

Opioid blockers that only affect the gut

Methylnaltrexone(Relistor) comes in both oral and injectable forms, while Naloxegol (Movantik)is an oral medication. Both medications are designed specifically for Opioid-Induced Constipation (OIC).

This post is intended for general informational purposes only and does not address any individual circumstances. It is not a substitute for professional medical advice, diagnosis or treatment. When in doubt, speak to your doctor.

If you think you may be experiencing overdose or have any other medical emergency, immediately call your doctor or dial 911.

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