Overview
Toxic megacolon means the colon (large bowel) has become widened and has stopped working, together with signs that the whole body is affected, such as fever, fast heartbeat and weakness. The inflamed bowel wall becomes thin and can tear. It is most often a complication of severe ulcerative colitis or Crohn's colitis, or of a severe bowel infection such as Clostridioides difficile infection.
Symptoms
Severe diarrhea, often bloody, that may suddenly lessen as the colon stops moving
Swollen, tender, distended abdomen
Abdominal pain that is constant and severe
Fever and chills
Fast heartbeat, weakness, dizziness
Dehydration, confusion or drowsiness
Self-Care Tips
If you have colitis and develop the warning symptoms, go to hospital immediately.
Do not take anti-diarrhea medicines or strong painkillers during a severe flare unless your doctor tells you to.
Never stop your colitis medicines on your own.
Keep your IBD team's contact details at hand and know when to call them.
When to See a Doctor
Seek medical care promptly if you notice: Swollen painful belly with fever and fast heartbeat in someone with colitis or severe diarrhea; Sudden worsening pain or a rigid, board-like abdomen; Confusion, fainting, very low urine output or cold clammy skin; Diarrhea suddenly stopping while your belly becomes more swollen and you feel worse.
Why it happens
Severe inflammation damages the muscle of the bowel wall so that it can no longer push contents along, and the colon fills with gas and widens. Bacteria and toxins may then enter the blood. Risk is higher with a severe flare that is not controlled, a serious infection of the colon, or stopping treatment suddenly. Certain medicines that slow the bowel, such as anti-diarrhea drugs, opioids and anticholinergics, can raise the risk during a severe flare, and a colonoscopy or bowel preparation during a severe flare may also be risky.
How common it is
It is uncommon today, because severe colitis is usually treated early, but it remains one of the most serious complications of inflammatory bowel disease and some infections of the colon.
How it is diagnosed
Doctors diagnose it from your symptoms, examination, blood tests showing inflammation or infection, and an abdominal X-ray or CT scan showing a widened colon. Stool tests look for infections. Colonoscopy is avoided because of the risk of perforation.
Lifestyle and daily habits
This is an emergency. There is no home treatment.
• If you have colitis and develop the warning symptoms, go to hospital immediately.
• Do not take anti-diarrhea medicines or strong painkillers during a severe flare unless your doctor tells you to.
• Never stop your colitis medicines on your own.
• Keep your IBD team's contact details at hand and know when to call them.
Diet
Diet is not a treatment for this emergency.
• In hospital you may be given nothing by mouth and fluids and nutrients through a drip.
• Food is restarted gradually once the colon is working again.
• Nutrition support and a dietitian may help during recovery.
Medicines
Treatment is given in hospital, often in a specialist unit.
• Intravenous fluids and correction of salts in the blood.
• Intravenous steroids or other anti-inflammatory treatment if the cause is severe colitis.
• Antibiotics when infection or perforation is a concern, or specific treatment if C. difficile is found.
• Medicines to prevent blood clots may be given while you are in bed.
• Rescue medical therapy for severe colitis is chosen by the specialist team.
Your hospital team decides all medicines.
Procedures and surgery
Surgery is a key part of treatment when medicines fail or complications occur.
• Emergency surgery is needed for perforation, heavy bleeding, or if the condition does not improve with treatment.
• The usual operation removes the colon, and an ileostomy (a bowel opening on the abdomen collecting waste in a bag) is often created; some patients can have reconnection or a pouch later.
• Stoma nurses and support groups help you live with a stoma.
Outlook
It is a dangerous condition, but early hospital treatment can settle the inflammation in some patients. If there is no clear improvement within a short time, or if the bowel perforates, emergency surgery is needed and can be life-saving. Outcomes are better when treatment starts early.
Questions to ask your doctor
• What caused this episode in my case?
• How do you decide whether I need surgery?
• What will life be like with a stoma, and can it be reversed?
• How can I lower the chance of severe flares in the future?
Source and review
This guide comes from the Saudi Gastroenterology Association (SGA) patient library, prepared by the Approved for publication by SGA; individual clinician review is ongoing. Last reviewed: 2026-04-24. It is for education and does not replace your doctor's advice.
Frequently Asked Questions
What is Toxic Megacolon?
How is Toxic Megacolon diagnosed?
What is the outlook for Toxic Megacolon?
When should I see a doctor about Toxic Megacolon?
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