Recurring constipation almost always has an identifiable cause, and often more than one. Fewer than three bowel movements per week, hard or lumpy stools, and straining during more than a quarter of your bathroom visits are the hallmarks of functional constipation. When these symptoms persist for three months or longer, something in your diet, medications, pelvic floor function, or gut biology is likely driving the pattern. Here’s what to look at.
You’re Probably Not Getting Enough Fiber
This is the most common and most fixable cause. More than 90 percent of women and 97 percent of men in the U.S. fall short of the recommended fiber intake, which works out to about 14 grams for every 1,000 calories you eat. For most adults, that means roughly 25 to 35 grams a day. If your diet leans toward processed foods, white bread, cheese, and meat, you’re likely getting half that or less.
Not all fiber works the same way, though, and this matters if you’ve tried adding fiber and it didn’t help. Soluble fiber that forms a gel and resists fermentation (psyllium husk is the classic example) retains water throughout the colon, softening hard stool and making it easier to pass. Coarse insoluble fiber, like the kind in whole vegetables and bran flakes, can stimulate the intestinal lining to secrete mucus and water, which also helps move things along. But finely ground insoluble fiber, the kind found in many processed “high-fiber” products, adds bulk without adding water. It can actually make constipation worse by increasing the dry mass of your stool.
If you’re going to increase your fiber intake, do it gradually over a week or two and drink more water alongside it. A sudden jump in fiber without enough fluid can leave you more bloated and backed up than before.
Medications That Slow Your Gut
If your constipation started or worsened around the time you began a new medication, that’s probably not a coincidence. Several common drug classes directly slow intestinal movement.
- Opioid painkillers are the biggest offenders, causing constipation in up to 80 percent of people who take them. They bind to receptors in the gut wall and reduce both muscle contractions and fluid secretion.
- Anticholinergic drugs (used for overactive bladder, certain stomach problems, and allergies, among other things) cause constipation in about 27 percent of users by dampening the nerve signals that drive digestion forward.
- Antidepressants, especially older tricyclics like amitriptyline, have strong anticholinergic effects. Even some newer antidepressants like paroxetine and venlafaxine can slow the gut.
- Blood pressure medications in the calcium channel blocker family, particularly verapamil and diltiazem, relax smooth muscle throughout the body, including in your intestines. About 7 percent of users develop constipation.
- Iron supplements cause oxidative stress in the gut, disrupt the bacterial balance, and slow transit.
- Diuretics pull water out of your body, leaving less available for your stool. They can also lower potassium levels, which weakens the muscle contractions that push stool forward.
If you suspect a medication is contributing, don’t stop it on your own, but it’s worth raising with whoever prescribed it. There are often alternative formulations or complementary strategies that help.
Your Pelvic Floor Muscles Aren’t Coordinating
This is one of the most underdiagnosed causes of chronic constipation, especially in women. A condition called dyssynergic defecation means the muscles of your pelvic floor aren’t working together properly when you try to have a bowel movement. Normally, the muscles holding stool in should relax when you bear down. In people with this condition, those muscles fail to relax or even tighten instead (called paradoxical contraction). Some people also can’t generate enough coordinated force to push stool out effectively.
About half of people with dyssynergic defecation also have a reduced ability to sense stool in the rectum or feel the urge to go. When stool sits in the rectum too long, it dries out and hardens, creating a cycle where each bowel movement becomes more difficult than the last. The good news is that biofeedback therapy, which trains you to coordinate these muscles correctly, is highly effective for this condition. If you strain constantly, feel like you can never fully empty, or need to use your fingers to help stool pass, this is worth investigating.
Methane-Producing Gut Bacteria
Your gut microbiome may be working against you. Certain microorganisms in the large intestine produce methane gas during digestion, and methane directly slows intestinal transit. This isn’t a fringe theory: the association between methane production and delayed transit has been confirmed across studies in healthy people, people with irritable bowel syndrome, and people with chronic constipation alike.
Among people with slow-transit constipation specifically, 58 to 75 percent test positive for methane production on a breath test, compared to only 13 to 28 percent of healthy controls. Methane appears to act on the neuromuscular system of the gut, reducing the strength and frequency of the contractions that push stool forward. If standard dietary changes and laxatives haven’t resolved your constipation, a breath test for methane overproduction is something a gastroenterologist can offer.
Thyroid Problems and Other Medical Causes
An underactive thyroid (hypothyroidism) slows down nearly every system in the body, and the gut is no exception. Thyroid hormones influence intestinal muscle cells both directly and through their interaction with the nervous system. When levels drop, the rhythmic contractions that move food through your digestive tract weaken and slow. Constipation is one of the earliest and most common symptoms of hypothyroidism, often appearing before other signs like fatigue, weight gain, or cold sensitivity become obvious.
Diabetes can also cause constipation over time by damaging the nerves that control gut motility. Neurological conditions like Parkinson’s disease and multiple sclerosis affect these same nerve pathways. Even chronic dehydration, which many people don’t recognize in themselves, reduces the water content of stool and makes it harder to pass.
Toilet Posture and Habit
The standard sitting toilet positions your rectum at an angle that actually works against easy elimination. When you sit upright on a toilet, the pelvic floor muscles that close off the anal canal remain partially engaged, creating a bend in the rectum that requires more straining to push past. Raising your knees about 35 degrees above your hips (roughly achieved by placing your feet on a low stool) straightens the rectal angle, relaxes the pelvic floor, and reduces the force needed to pass stool.
Timing habits matter too. Your colon is most active in the morning and after meals, driven by a reflex triggered by eating. Ignoring the urge to go, whether because of a busy schedule or discomfort using public restrooms, trains the rectum to tolerate larger volumes of stool before signaling urgency. Over time, this blunts the urge entirely and allows stool to dry out further in the rectum.
What Laxatives Can and Can’t Do
Osmotic laxatives like polyethylene glycol (MiraLAX) work by drawing water into the colon. They typically produce a bowel movement within one to three days. They’re generally safe for short-term use and can break a cycle of hard, impacted stool, but they don’t fix the underlying reason you’re constipated. If you find yourself reaching for a laxative every week, that’s a signal to investigate the cause rather than keep managing the symptom.
Stimulant laxatives work faster but can cause cramping, and long-term daily use can make your colon less responsive over time. Fiber supplements, particularly psyllium, function differently from both. They normalize stool consistency by holding water in a gel matrix that resists dehydration as stool moves through the colon. For many people, a psyllium-based supplement taken daily with plenty of water is more effective than occasional laxative use.
Signs That Need Prompt Attention
Most recurring constipation is functional, meaning it’s driven by diet, habits, medications, or pelvic floor issues rather than something structurally wrong. But certain changes warrant prompt evaluation: blood in your stool (red or black), stools that become persistently thin or ribbon-shaped, unexplained weight loss, new abdominal pain you can’t account for, or a persistent feeling that you can’t finish passing stool. These can overlap with symptoms of colorectal conditions that benefit from early detection.