Chronic constipation rarely has a single cause. It develops when one or more factors slow the movement of stool through your colon, make it harder to pass, or disrupt the coordination your body needs to have a bowel movement. Roughly 12% of adults worldwide meet the formal diagnostic criteria, and the condition is nearly twice as common in women as in men.
To qualify as chronic, constipation symptoms need to have been present for at least three months, with the pattern starting six months or more before diagnosis. That means fewer than three bowel movements per week, frequent straining, hard or lumpy stools, or a persistent feeling that you haven’t fully emptied. Most people with chronic constipation have two or more of these symptoms happening during at least a quarter of their bowel movements.
Low Fiber, Dehydration, and Inactivity
The most common starting point is diet. Adults need between 22 and 34 grams of fiber per day, depending on age and sex, and most people fall well short. Fiber adds bulk to stool and helps it retain water, which keeps it soft enough to move through the colon at a normal pace. When your diet is low in fruits, vegetables, whole grains, and legumes, stool dries out and slows down.
Not drinking enough water compounds the problem. Your colon absorbs water from stool as it passes through, so if you’re already mildly dehydrated, the colon pulls out more than it should, leaving stool hard and difficult to pass. Physical inactivity plays a role too. Regular movement stimulates the natural contractions of your intestinal muscles. Prolonged sitting or a sedentary lifestyle weakens those contractions over time.
Two Types of Motility Problems
When lifestyle factors don’t fully explain the problem, there are two main physiological patterns at work, and they often overlap.
Slow transit constipation means the muscles of your colon contract too slowly or too weakly, so stool takes longer than normal to travel its full length. The longer stool sits in the colon, the more water gets absorbed, making it progressively harder and more difficult to pass. People with this pattern may go many days between bowel movements and feel bloated or uncomfortable in the meantime.
Pelvic floor dyssynergia is a coordination problem. Normally, when you bear down to have a bowel movement, the muscles of your pelvic floor relax to let stool pass. In dyssynergia, those muscles tighten instead of relaxing, creating a functional blockage. You strain hard but feel like nothing is moving, or like you can never fully empty. About 60% of people diagnosed with pelvic floor dyssynergia also have slow transit, so the two frequently coexist and reinforce each other.
Medications That Slow the Gut
Several common drug classes cause constipation as a direct side effect, and when you take them long term, the constipation becomes chronic. Opioid pain medications are the most well-known culprits. They bind to receptors in your intestinal wall and dramatically slow contractions throughout the digestive tract.
Antidepressants and antipsychotics, particularly older ones with strong effects on the nervous system’s signaling chemicals, reduce gut motility in a similar way. Iron supplements are a frequent offender, especially at higher doses. Blood pressure medications in the calcium channel blocker class can also slow things down. Cancer treatments, including many chemotherapy drugs, are among the most commonly reported causes in side-effect databases. If your constipation started around the time you began a new medication, that connection is worth exploring with whoever prescribed it.
Hormonal and Metabolic Disruptions
Your thyroid gland has a surprisingly large influence on your gut. Hypothyroidism, where the thyroid produces too little hormone, slows gastrointestinal movement by weakening the neuromuscular signals that drive intestinal contractions. It can also cause physical changes in the intestinal wall itself, including thickening of the muscle layer and shortening of the tiny finger-like projections that line the intestine. These structural changes further impair motility. Constipation is one of the earliest and most common symptoms of an underactive thyroid, and it often improves once thyroid hormone levels are corrected.
Diabetes can damage the nerves that control gut movement over time, leading to sluggish transit. High blood calcium levels, which can result from overactive parathyroid glands or other conditions, also slow colonic contractions. Pregnancy is another hormonal state that commonly triggers constipation, both from rising progesterone levels and from the physical pressure of a growing uterus on the intestines.
Neurological Conditions
The gut has its own nervous system, sometimes called the “second brain,” containing hundreds of millions of nerve cells that coordinate the rhythmic contractions pushing stool forward. Diseases that damage the nervous system frequently disrupt this process.
Parkinson’s disease is one of the strongest examples. The same abnormal protein deposits that accumulate in the brain also build up in the nerve networks of the colon, often years before the tremor and movement symptoms appear. Constipation in Parkinson’s results from a combination of generally slowed body movement, reduced gut contractions, and paradoxical tightening of the pelvic floor during attempts to defecate.
Multiple sclerosis affects bowel function in over 50% of patients. The disease damages the nerve pathways running from the brain and spinal cord to the sacral nerves that control the colon and pelvic floor, leading to constipation, difficulty emptying, and sometimes fecal incontinence. Spinal cord injuries cause similar disruption. Between 27% and 62% of people with spinal cord injuries develop chronic bowel problems, primarily because the injury cuts off the brain’s ability to coordinate colonic contractions and sphincter relaxation.
Structural Abnormalities
Physical changes in the anatomy of the rectum and pelvic floor can create a mechanical barrier to passing stool, even when transit through the colon itself is normal.
A rectocele forms when the tissue separating the rectum from the vagina weakens, allowing the front wall of the rectum to bulge forward. Small rectoceles under 1 centimeter rarely cause symptoms, but those larger than 2 centimeters can trap stool in the bulging pocket, making evacuation difficult. Some people with rectoceles find they need to press on the back wall of the vagina to push stool out.
Internal rectal prolapse happens when the rectum folds in on itself, like a telescope, during straining. The folded tissue blocks the passage of stool and creates a sensation of incomplete emptying. This condition can be found on imaging in up to 40% of women without symptoms, so its presence alone doesn’t always explain constipation. But when the prolapse is significant, it acts as a real obstruction. About half of people with internal rectal prolapse also have a rectocele or other pelvic floor issue, making the outlet problem worse.
The Gut-Brain Connection and Stress
Chronic stress and anxiety don’t just make you feel tense. They alter the chemical environment of your gut through a communication network linking your brain, your gut’s own nervous system, and the trillions of bacteria living in your intestines. This network runs in both directions: your brain influences gut motility and secretion, and your gut sends signals back that affect mood and cognition.
A key chemical messenger in this system is serotonin. Most people associate it with mood, but roughly 95% of the body’s serotonin is produced in the gut, where it regulates intestinal contractions, fluid secretion, and the sensitivity of gut nerves. Chronic stress can disrupt serotonin signaling in the gut, slowing motility and contributing to constipation. This helps explain why constipation so often accompanies anxiety and depression, and why it can worsen during periods of high stress even when diet and activity haven’t changed.
Shifts in Gut Bacteria
People with chronic constipation tend to have a different bacterial makeup in their intestines compared to people with regular bowel habits. Specifically, they often have lower levels of beneficial bacteria like Bifidobacterium and higher levels of certain other bacterial groups in the lining of the colon. While no single bacterial “signature” has been confirmed, the pattern suggests that imbalances in gut bacteria play a role in how quickly stool moves through the intestines.
One of the more specific findings involves methane-producing microbes. People with chronic constipation harbor more of these organisms than average. Methane gas appears to directly slow intestinal contractions, and higher methane levels on breath tests correlate with slower transit times. Treatments that reduce methane-producing bacteria have shown improvements in bowel frequency, reinforcing the idea that these microbes are active contributors to the problem rather than just bystanders.