What are the side effects of Alvimopan?
Last updated September 7, 2026.
**The most common side effects of alvimopan are indigestion, constipation, gas, back pain, low potassium, anemia, and trouble passing urine.** Alvimopan (brand name Entereg) is a hospital-only medicine given for a few days after bowel surgery to help your intestines start moving again, so its side effects show up while you are still being monitored. Because it blocks opioid effects in the gut without blocking pain relief, some people get belly cramping or loose stools, and that is more likely if you were taking opioids regularly before surgery. It carries a boxed warning about a higher rate of heart attack seen in a long-term study of people using opioids for chronic pain, which is why use is capped at 15 doses in the hospital. Your team will check your potassium and blood counts and watch how your bowels and bladder respond. Report severe diarrhea, worsening belly pain, chest pain, or inability to urinate right away.
What to do
- Expect hospital use only: Alvimopan is stocked through a restricted program and given for up to 15 doses in the hospital, so you will not fill it at a pharmacy.
- Share your opioid history: Tell the surgical team if you took opioids daily in the week before surgery, since that raises the chance of cramping and diarrhea and can rule out the drug.
- Track your bowels and bladder: Tell your nurse if diarrhea becomes severe, belly pain worsens, or you cannot pass urine, because each changes how the medicine is managed.
- Ask about your labs: Low potassium and anemia are picked up on routine blood draws after surgery and are usually corrected while you are still admitted.
- Report chest symptoms fast: Chest pain, pressure, or new shortness of breath needs immediate attention, not a wait-and-see approach.
- Bring questions to a clinician: A surgeon, hospitalist, or pharmacist can tell you whether a symptom is from alvimopan, from surgery, or from your other medicines.
Related questions
- Are medication side effects worse at first
- Can i get health insurance outside open enrollment
- Can i see what my doctor wrote about me
- Can i text a doctor about medication side effects