An ileus is a temporary slowdown or complete halt of the normal wave-like muscle contractions that move food through your intestines. Unlike a physical blockage such as a tumor or scar tissue, nothing is structurally obstructing the bowel. The gut simply stops working. This distinction matters because the causes, treatment, and outlook differ significantly from a mechanical obstruction, even though many symptoms overlap.
How an Ileus Differs From a Blockage
Your intestines move food along through coordinated muscle contractions called peristalsis. In a mechanical bowel obstruction, something physically blocks that path: adhesions from prior surgery, a hernia, or a tumor. In an ileus (sometimes called paralytic ileus or pseudo-obstruction), the pathway is wide open but the muscles have stopped contracting. The bowel is essentially paralyzed.
This difference can be surprisingly hard to detect on imaging. On an X-ray, an ileus can look like a small bowel obstruction if the colon isn’t dilated, and a type of large-bowel ileus called Ogilvie syndrome can mimic a mechanical blockage because it causes the same pattern of dilation upstream and decompression downstream. CT scans are more reliable because they can identify a “transition zone,” the specific point where dilated bowel meets collapsed bowel, which signals a physical obstruction. When no transition zone exists, an ileus is more likely.
Common Causes
Surgery is the single most common trigger. Some degree of ileus is nearly universal after abdominal surgery, and up to 25% of patients who have elective abdominal procedures develop a clinically significant ileus. Colorectal surgery carries the highest risk, with prolonged ileus occurring in 5% to 30% of cases. Larger incisions and more handling of the intestines during surgery increase the odds, which is one reason laparoscopic (minimally invasive) approaches tend to produce shorter recovery times.
Outside the operating room, several other factors can trigger an ileus:
- Medications: Opioid painkillers are the most well-known culprit, but antipsychotics, older antidepressants, overactive-bladder drugs, and certain chemotherapy agents all slow gut motility. Even common over-the-counter anti-diarrheal drugs like loperamide can contribute.
- Electrolyte imbalances: Abnormal levels of potassium, sodium, calcium, or chloride disrupt the electrical signals that drive intestinal contractions. This is especially common in hospitalized patients on IV fluids or those with kidney disease.
- Infections: Severe abdominal infections like appendicitis or peritonitis, as well as intestinal infections from bacteria or viruses, can shut down bowel activity.
- Reduced blood supply: When blood flow to the intestines drops, whether from low blood pressure, a blood clot, or shock, the gut muscles can’t function normally.
- Lung or kidney disease: Serious illness affecting other organs can reflexively slow the bowel, likely through inflammation and nerve signaling.
What It Feels Like
Postoperative ileus typically shows up between the third and fifth day after surgery. The hallmark symptoms are nausea, vomiting, a bloated and tight abdomen, and a complete inability to pass gas or have a bowel movement. The belly often looks visibly swollen and sounds hollow when tapped, a finding doctors call tympanism. Bowel sounds, which you can sometimes hear with a stethoscope or even unaided, are sparse or completely absent.
When ileus occurs outside of surgery, the picture is similar but develops more gradually. Progressive bloating is the most common complaint, reported by about 80% of people. Roughly 60% experience abdominal pain and nausea or vomiting, and close to half have either constipation or, paradoxically, diarrhea. The pain tends to be diffuse and achy rather than the sharp, cramping waves typical of a mechanical obstruction.
Why It Can Become Dangerous
Most ileus episodes resolve on their own within a few days, but when the gut stays paralyzed for too long, the consequences escalate quickly. Fluid normally secreted into the intestines can’t be reabsorbed, leading to progressive dehydration and electrolyte imbalances that feed a vicious cycle, since those same imbalances worsen the ileus. Gas and fluid accumulate, stretching the bowel wall and increasing pressure inside the intestine.
If the bowel remains obstructed beyond roughly 48 hours, the rising pressure can compromise blood flow to the intestinal wall itself. Once the wall becomes damaged, bacteria and toxins that are normally contained inside the gut can leak into the abdominal cavity, causing a serious infection called peritonitis, or enter the bloodstream and trigger widespread inflammation. In rare cases, the stretched bowel wall can perforate entirely. An untreated, prolonged ileus can be fatal, progressing through the same dangerous sequence as an untreated mechanical obstruction.
How It’s Diagnosed
Doctors typically start with a plain abdominal X-ray. In an ileus, you’ll see dilated loops of both small and large bowel with gas spread diffusely throughout the intestines. This pattern contrasts with mechanical obstruction, where dilation is usually confined to one section and the bowel beyond the blockage is collapsed and gas-free. Certain X-ray clues help tell them apart: when two air-fluid levels within the same loop of bowel differ in height by 2 cm or more, the specificity for a true obstruction exceeds 95%.
When the X-ray is ambiguous, a CT scan with contrast is the next step. CT provides a much clearer picture, pinpointing whether a transition zone exists and revealing potential causes like abscess, inflammation, or tumor. It can also measure bowel diameter precisely. Small bowel wider than 2.5 cm, colon wider than 6 cm, and the cecum (the first part of the large intestine) wider than 9 cm all indicate significant dilation.
Treatment and Recovery
The core approach to managing an ileus is supportive: rest the gut and correct whatever triggered the problem. This means no food or drink by mouth initially, intravenous fluids to maintain hydration and restore electrolyte balance, and a tube passed through the nose into the stomach if the buildup of gas and fluid is severe enough to need drainage. Any offending medications, particularly opioids, are reduced or stopped when possible.
For people who need opioid pain relief after bowel surgery, a medication that blocks opioid effects specifically in the gut (without reducing pain control) can speed recovery. It’s given as a capsule before surgery and continued twice daily afterward for up to seven days. This targeted approach helps the intestines resume normal function while the brain still gets pain relief.
One of the simplest interventions with surprisingly strong evidence is chewing gum. A meta-analysis of 17 randomized trials involving over 1,300 patients found that gum chewing after abdominal surgery reduced the time to first passing gas by about a third of a day, sped up the first bowel movement by about half a day, and shortened hospital stays by nearly three-quarters of a day. The mechanism is “sham feeding”: chewing stimulates the same nerve pathways that activate when you eat, jumpstarting the gut’s motility without actually putting food into a bowel that isn’t ready for it.
How Long Recovery Takes
The timeline depends heavily on the type of surgery and how much of the bowel was handled. Under modern fast-track recovery protocols, patients who’ve had small bowel surgery tolerate solid food at a median of about 3 hours after the procedure, pass gas around 18 hours, and have their first bowel movement around 49 hours. Colon surgery takes longer: patients typically tolerate solids within 14 to 16 hours, but passing gas can take 17 to 44 hours, and the first bowel movement doesn’t arrive until roughly 46 to 70 hours depending on which part of the colon was removed. Right colon resections tend to have the slowest gut recovery.
For a non-surgical ileus, recovery varies with the underlying cause. Correcting an electrolyte imbalance or stopping an offending medication can produce improvement within 24 to 48 hours. Ileus caused by a severe abdominal infection may take longer to resolve, because the inflammation driving the paralysis persists until the infection is controlled. In either case, the clinical milestones are the same: passing gas is the first reliable sign that the bowel is waking up, followed by tolerating liquids, then solid food, and finally a bowel movement.
Factors That Raise Your Risk
Certain situations make an ileus more likely. Open surgery carries a higher risk than laparoscopic surgery, and procedures that involve cutting and reconnecting the bowel (like colorectal resections) carry higher risk than operations where the intestines are barely touched, such as gallbladder removal. Heavy opioid use after surgery is one of the most modifiable risk factors. Being immobilized in bed for extended periods also slows gut recovery, which is why surgical teams now encourage patients to walk as soon as possible after an operation.
Outside of surgery, people taking multiple medications that slow gut motility face compounding risk. An older adult on an opioid for pain, an antipsychotic for mood, and an overactive-bladder drug is exposed to three different classes of medication that all independently reduce intestinal movement. Chronic kidney disease and prolonged critical illness also predispose the bowel to shutting down, largely through the electrolyte disturbances and inflammation they cause.