A bowel blockage, also called an intestinal obstruction, happens when something prevents food, liquid, and gas from moving through your small or large intestine normally. The blockage causes contents to back up, stretching the intestine above the blocked point and creating pressure, pain, and potentially dangerous complications. It’s a common surgical emergency, and delays in treatment are linked to longer hospital stays and higher rates of complications.
Two Types of Bowel Blockage
Bowel blockages fall into two broad categories: mechanical and functional. A mechanical blockage means something is physically blocking the intestine, like scar tissue, a hernia, or a tumor. The intestine above the blockage stretches and fills with trapped fluid and gas, while the intestine below it stays empty and collapsed. This creates a visible “transition point” that doctors can identify on imaging.
A functional blockage (often called paralytic ileus) has no physical barrier at all. Instead, the muscles lining the intestinal wall stop contracting and pushing contents forward. The result looks and feels similar to a mechanical blockage: fluid pools in the intestine, the bowel swells, and bacteria begin to multiply in the stagnant contents. Functional blockages commonly happen after abdominal surgery, during serious infections, or as a side effect of certain medications.
What Causes a Blockage
In adults, the three most common causes are adhesions, hernias, and colon cancer. Adhesions are bands of scar tissue that form inside the abdomen after surgery. They can kink, twist, or compress a loop of intestine years or even decades after the original operation. Hernias occur when a section of intestine pushes through a weak spot in the abdominal wall and gets trapped. Colon cancer can grow large enough to narrow or completely block the large intestine.
Other causes include strictures from inflammatory conditions like Crohn’s disease or diverticulitis, and volvulus, where the intestine twists around itself. In children, the most common cause is intussusception, a condition where one segment of intestine slides inside an adjacent segment like a collapsing telescope.
Several classes of medication can also trigger functional blockages. Opioid painkillers are among the most well-known culprits, but the list also includes certain antipsychotic drugs, anticholinergics (used for bladder problems and other conditions), some diabetes medications, and chemotherapy agents. Cancer patients face especially high risk because they often deal with multiple contributing factors at once: reduced physical activity, dehydration from diuretics, pain medications, and the direct effects of certain chemotherapy drugs on the nerves controlling gut movement.
What It Feels Like
The hallmark symptom is crampy abdominal pain that comes in waves. The intestine above the blockage contracts forcefully, trying to push contents past the obstruction, which produces intense cramping that builds, peaks, and temporarily eases before returning. This wave pattern typically repeats every few minutes.
Nausea and vomiting are almost universal with small bowel blockages. When the blockage is high up in the small intestine, vomiting starts early and may be green or yellow from bile. When the blockage is lower or in the large intestine, vomiting may develop later and can have a fecal odor because bacteria have been fermenting trapped contents for longer.
Bloating and visible abdominal swelling develop as gas and fluid accumulate. With a complete blockage, you stop passing gas and stool entirely, a symptom called obstipation. A partial blockage may still allow some gas or watery stool to pass, which can make the condition harder to recognize at first. Many people also lose their appetite completely and feel increasingly unwell as the obstruction persists.
Partial vs. Complete Blockage
This distinction matters because it changes how urgent treatment is and whether surgery is likely. A partial blockage still allows some intestinal contents to pass through. Symptoms tend to be less severe, and many partial blockages resolve with hospital-based supportive care: IV fluids to prevent dehydration, a tube passed through the nose into the stomach to relieve pressure and nausea, and a period of fasting to let the bowel rest. Most partial blockages caused by adhesions will open up on their own within 24 to 72 hours with this approach.
A complete blockage is more serious. Nothing gets past the obstruction, pressure builds rapidly, and the risk of complications climbs with every hour. Complete blockages are more likely to need surgery, especially when they don’t improve with initial supportive care or when there are signs that the intestine’s blood supply is being compromised.
How Doctors Diagnose It
A CT scan is the primary tool. For bowel obstruction overall, CT scans have a pooled sensitivity of about 90% and specificity of about 89%, meaning they correctly identify blockages the vast majority of the time. For small bowel obstruction specifically, CT has around 83% sensitivity with a high negative predictive value of 91%, making it particularly reliable for ruling out a blockage when results are normal. For large bowel obstruction, sensitivity and specificity are around 85% and 83%.
The scan reveals where the blockage is, what’s likely causing it, and whether the intestine shows signs of compromised blood flow. Plain abdominal X-rays can show dilated loops of bowel and air-fluid levels, but CT provides far more detail and has largely become the standard first-line imaging study for suspected obstruction.
Treatment: What to Expect
Initial treatment in the hospital focuses on stabilizing you and relieving pressure. You’ll receive IV fluids to replace what your body has been losing into the swollen intestine (the bowel can sequester surprisingly large volumes of fluid). A thin, flexible tube is typically placed through your nose and down into your stomach to suction out accumulated gas and liquid, which usually provides significant relief from nausea and bloating. You won’t eat or drink anything by mouth during this time.
For many partial blockages, especially those caused by adhesions, this conservative approach is enough. The bowel gradually opens up, and you’ll know it’s working when you start passing gas again. Once that happens, the medical team slowly reintroduces clear liquids and then solid food.
Surgery becomes necessary when conservative treatment fails, when the blockage is complete and won’t resolve on its own, or when there’s concern about strangulation (the intestine’s blood supply being cut off). During surgery, the cause of the blockage is addressed directly: adhesions are cut, a hernia is repaired, or a section of damaged intestine is removed. Research has shown that delays in getting to surgery are directly linked to higher rates of postoperative complications and longer hospital stays. For blockages caused by hernias in particular, surgical delays have been associated with increased mortality.
When a Blockage Becomes Dangerous
The most feared complication is strangulation, where the blockage also cuts off blood flow to the affected segment of intestine. Without blood supply, the tissue begins to die (necrosis), which can lead to perforation, where the intestinal wall breaks open and spills bacteria-laden contents into the abdominal cavity. This causes peritonitis and sepsis, both life-threatening conditions.
Warning signs that a blockage may be progressing toward strangulation include a shift from crampy, intermittent pain to constant, severe pain; fever; a rapid heart rate; and a rigid, extremely tender abdomen. At this stage, emergency surgery is necessary. If a patient becomes hemodynamically unstable, meaning their blood pressure drops and doesn’t respond to aggressive fluid replacement, they go directly to the operating room for emergency exploration.
Risk Factors to Know
The single biggest risk factor for a bowel blockage is previous abdominal or pelvic surgery. Adhesions form in an estimated 90% or more of people who undergo open abdominal surgery, though only a fraction of those adhesions ever cause a blockage. The risk persists for life, and a person can develop an adhesion-related obstruction 20 or 30 years after their original operation.
Other risk factors include a history of Crohn’s disease or other inflammatory bowel conditions, abdominal or pelvic cancers, prior radiation therapy to the abdomen, and hernias that haven’t been repaired. Older adults face higher overall risk because they’re more likely to have had prior surgeries, use medications that slow gut motility, and have conditions like colon cancer. Reduced physical activity and chronic constipation can also contribute, particularly in people who are already taking medications that slow the bowel.