Naloxegol: what it treats, how to take it, side effects
Last updated September 3, 2026.
Naloxegol is a peripherally acting mu-opioid receptor antagonist - it shields the bowel from opioid effects while leaving pain relief alone. You may know it as Movantik. For the constipation that opioid pain treatment brings along.
What does it treat?
Constipation caused by opioid pain medications in adults with chronic, non-cancer pain.
How do you take it?
Once a day on an empty stomach - at least 1 hour before or 2 hours after the first meal of the day, same time daily - exactly as directed. Missed dose: take it when you remember unless the next one is close; never double up.
Side effects to know
- Common: diarrhea, nausea, gas, stomach pain, vomiting, headache, sweating, chills.
- Serious - stop taking it and call your doctor immediately: severe or worsening stomach pain and diarrhea; the allergic set - rash, hives, swelling of face, lips, throat, tongue, hands, or feet; and the opioid-withdrawal set - sweating, chills, anxiety, irritability, yawning, muscle aches: the shield can tilt too far.
Who should not take it?
Bowel obstruction or high risk of one rules it out. Flag stomach or intestinal conditions - ulcers, Crohn's, diverticulitis, cancer of the gut - and kidney or liver disease. Certain antibiotics and antifungals clash; grapefruit is out. If your opioid stops, this stops too - tell your doctor. If you become pregnant, call your doctor.
When is it an emergency?
Severe stomach pain, uncontrolled diarrhea with weakness, or face or throat swelling is urgent care. For an overdose, call Poison Control at 1-800-222-1222. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
How can it fix the constipation without hurting pain relief?
The peripheral trick: naloxegol blocks opioid receptors in the gut - where opioids paralyze the bowel - while staying mostly out of the brain, where the pain relief lives. The shield is targeted. The rare failure mode is tilting too far: the withdrawal set - sweating, chills, anxiety, irritability, yawning, muscle aches - means some blockade reached the wrong place: stop and call the doctor.
Why on an empty stomach?
Absorption: food changes how much drug reaches the blood - the rule is at least 1 hour before or 2 hours after the first meal of the day, same time daily. First thing in the morning, coffee and breakfast after the wait - the anchor is the alarm clock, not the kitchen. Grapefruit is out for the same family of reason: it changes the level.
What is the severe-stomach-pain warning?
The stop-and-call set: severe or worsening stomach pain with diarrhea - the label says stop taking it and call immediately or get emergency care. On a drug that accelerates the gut, that pattern can mean the gut wall is suffering - it is never ridden out. Bowel obstruction or high risk of one rules the drug out from the start for the same reason.
What if I stop my opioid?
Then this stops too: naloxegol exists to counter the opioid's gut effect - no opioid, no job, and the label says to tell your doctor when the pain medication ends. The pair moves together: starting, stopping, and dose changes on one side are conversations on the other. Never keep it running out of habit.
Why did they ask about my stomach history?
The gut wall is the workplace: ulcers, Crohn's, diverticulitis, gut cancers, and any blockage history shape or rule out the choice - accelerating a diseased bowel has real risks. Kidney and liver disease adjust the dose. Certain antibiotics and antifungals clash - the everything-you-take list again.
What happens if I miss a dose of naloxegol?
Take it as soon as you remember, unless it is almost time for the next one - then skip it and never double up. The empty-stomach rule still applies to a makeup: an hour clear of food. One missed day usually means a slower gut day; the pattern that matters is the one your diary shows your doctor.