CONDITION
Constipation and Megacolon
Constipation describes difficulty passing faeces, or passing them less often than usual. What an owner typically notices first is straining in the litter tray or on a walk, sometimes with only small, hard stools produced—or none at all. In some animals the problem resolves with minor change, but in others it persists or worsens, and the colon can become stretched and less able to move waste along. When that happens, the term megacolon may be used. Owners often arrive here wondering whether what they are seeing is constipation or something else, how long to wait, and what might be contributing. The signs can overlap with urinary straining, and the causes range from diet and dehydration to structural problems, pain, or disease elsewhere in the body. This page walks through what constipation and megacolon look like in practice, what may be happening beneath the surface, how the picture is built through history and examination, and the range of approaches—dietary, medical, and surgical—that may be considered depending on severity and cause.
Why this matters now
Constipation is one of the most common gastrointestinal problems in cats, particularly affecting middle-aged to older animals. Certain factors may increase susceptibility, including obesity, dehydration, reduced activity, and diets low in fibre. Male cats appear somewhat more prone to developing megacolon, and some cases have an underlying neuromuscular component.
Constipation often begins intermittently, with occasional episodes of straining or reduced defecation frequency. Without management, the colon may become increasingly stretched and weakened over time. In megacolon, the colon loses its ability to contract effectively, becoming permanently dilated and incapable of normal function. This progression from simple constipation to megacolon can occur over months to years.
Signals & patterns
Early signals
Straining in the litter tray
Cats may spend extended time attempting to defecate, sometimes with visible effort but little result.
Hard, dry faeces
Stools may appear smaller than normal, dry, or pellet-like when passed.
Reduced frequency of defecation
Going longer than two days without passing faeces may indicate developing constipation.
Decreased appetite
Cats with faecal retention often eat less, likely due to abdominal discomfort or nausea.
Later signals
Vomiting
Severe constipation can trigger vomiting due to abdominal pressure and discomfort.
Visible abdominal distension
The abdomen may appear enlarged due to an impacted, distended colon.
Passing small amounts of liquid faeces
Paradoxically, liquid stool may pass around an impaction, sometimes mistaken for diarrhoea.
Lethargy and withdrawal
Cats with chronic constipation often become quiet and less interactive.
Click to read about the biological mechanisms
How this is usually investigated
Assessment of constipation involves physical examination, imaging to evaluate colonic size and content, and tests to identify any underlying causes.
Physical examination
Abdominal radiographs
Blood tests
Thyroid testing
Options & trade-offs
Management depends on severity and chronicity. Approaches range from dietary modification to surgical intervention for refractory megacolon.
Dietary management
Increased fibre, adequate hydration, and sometimes wet food diets.
Trade-offs: Appropriate for mild cases. Some cats do better with higher fibre whilst others respond to lower-residue diets. Finding the right balance may take time.
Laxatives and stool softeners
Medications to increase water content of faeces or stimulate colonic movement.
Trade-offs: Various types work differently. May need regular or intermittent use depending on individual response. Some are given orally, others added to food.
Manual evacuation under anaesthesia
Removal of impacted faeces when severe obstipation is present.
Trade-offs: Provides immediate relief but does not address underlying cause. May need to be repeated in chronic cases. Requires anaesthesia.
Prokinetic medications
Drugs to enhance colonic contractions.
Trade-offs: May help cats with mild to moderate motility issues. Less effective once megacolon has developed.
Subtotal colectomy
Surgical removal of most of the colon.
Trade-offs: Considered for refractory megacolon when medical management fails. Most cats do well long-term, though initial loose stools are common.
Common misconceptions
"Cats that strain are always constipated"
Straining in the litter tray can also indicate urinary problems or colitis with small frequent stools. Distinguishing between straining to defecate versus urinate is important.
"Constipation is just a minor inconvenience"
Chronic constipation can cause significant discomfort, appetite loss, and may progress to megacolon if not managed. Early intervention often achieves better outcomes.
"Once a cat has megacolon, nothing can help"
Many cats with megacolon can be managed medically for extended periods, and surgery can offer good quality of life when medical management is insufficient.
Observing litter tray habits including frequency, stool consistency, and any straining provides valuable baseline information. Noting water intake, activity levels, and appetite changes may help identify patterns. Multiple water sources and encouraging hydration through wet food can support digestive health.
Last reviewed: 24 April 2026 · Dr Alastair Greenway MRCVS