Constipation usually comes down to one of a few things: not enough fiber, not enough movement, a medication side effect, or a coordination problem with the muscles involved in pooping. Less commonly, it signals an underlying health condition. The good news is that most causes are fixable once you identify them.
Clinically, constipation means you’re straining during more than a quarter of your bowel movements, passing hard or lumpy stools at least that often, or going fewer than three times per week. If that pattern has lasted two months or more, it’s considered chronic.
Your Colon Is Absorbing Too Much Water
Understanding the basic plumbing helps explain almost every cause on this list. Your colon receives about 1.5 liters of fluid from the small intestine each day and absorbs most of it, leaving only about 100 milliliters (a few tablespoons) in the stool. The longer stool sits in the colon, the more water gets pulled out of it. That’s why anything that slows transit, whether it’s diet, inactivity, or a medical condition, produces harder, drier stool that’s more difficult to pass.
You’re Not Eating Enough Fiber
Adults need 25 to 30 grams of fiber per day, and most people globally fall short. Fiber holds water in the stool and adds bulk, which stimulates the colon’s wave-like contractions. Without it, stool compacts and moves sluggishly.
The fix isn’t complicated, but it needs to be gradual. Adding a big spike of fiber all at once can cause bloating and gas. Increasing intake by a few grams every few days, through vegetables, whole grains, legumes, and fruit, gives your gut time to adjust. Soluble fiber (found in oats, beans, and apples) forms a gel that softens stool, while insoluble fiber (found in wheat bran, nuts, and leafy greens) adds bulk and speeds things along.
Dehydration Matters, but Only If You’re Actually Dehydrated
You’ve probably heard that drinking more water helps constipation. The reality is more nuanced. A study of healthy volunteers found that adding one to two extra liters of fluid per day, whether water or a sports drink, did not increase stool output at all. It just increased urine output. If you’re already reasonably hydrated, gulping extra water won’t soften your stool.
Where hydration does matter is when you’re genuinely low on fluids, from illness, heavy sweating, or simply not drinking much. In that case, your colon compensates by pulling more water from stool to maintain your body’s fluid balance, and things dry out. The takeaway: drink enough to keep your urine light yellow, but don’t expect water alone to cure constipation.
A Medication Could Be the Cause
Constipation is one of the most common drug side effects, and several widely prescribed medication classes are known culprits:
- Opioid painkillers slow the entire gut. Even short courses after surgery or dental work can cause significant backup.
- Antidepressants, particularly older types with anticholinergic effects, reduce the signals that tell your intestines to contract.
- Antipsychotic medications can have similar anticholinergic effects.
- Iron supplements are a frequent offender, especially the forms prescribed for anemia.
- Anticancer drugs commonly cause constipation as a side effect of treatment.
- Potassium binders, used for high potassium levels, list constipation as a serious side effect.
If your constipation started around the same time as a new prescription, that connection is worth raising with whoever prescribed it. Sometimes a different formulation, adjusted dose, or a scheduled stool softener can solve the problem without stopping the medication.
You’re Not Moving Enough
Physical activity stimulates the wave-like contractions that push stool through the colon. Research measuring colon transit time found that women with high activity levels had significantly faster total transit than those with low or moderate activity. The effect was consistent: more activity correlated with shorter transit at every segment of the colon. The data was less clear-cut in men, but the overall trend still favored movement.
You don’t need to train for a marathon. Regular walking, cycling, or any activity that gets your body moving for 20 to 30 minutes most days makes a measurable difference. Prolonged sitting, on the other hand, lets everything slow down.
Your Pelvic Floor Muscles Aren’t Cooperating
Sometimes the problem isn’t transit speed. Stool arrives in the rectum just fine, but you can’t get it out. This is called dyssynergic defecation, and it’s more common than most people realize.
Your pelvic floor is a group of muscles that helps control bowel movements. Normally, these muscles relax when you bear down to poop. In dyssynergic defecation, they fail to relax, or they actually tighten instead (called paradoxical contraction). Some people also can’t generate enough pushing force, and about half of those with this condition have a reduced ability to feel the urge to go.
This type of constipation feels different. You sense that stool is right there but it won’t come out, no matter how much you strain. Biofeedback therapy, which retrains the muscle coordination, is the primary treatment and has strong success rates.
An Underlying Health Condition
Several medical conditions slow the gut as a secondary effect. Hypothyroidism is one of the most common. Low thyroid hormone levels cause substances to accumulate in the smooth muscle and connective tissue of the GI tract, delaying bowel transit. People with untreated hypothyroidism can also have delayed stomach emptying. The constipation typically improves once thyroid levels are corrected with replacement therapy.
Diabetes, neurological conditions like Parkinson’s disease, and autoimmune disorders can also impair the nerves or muscles that drive gut motility. If your constipation is persistent and doesn’t respond to diet and lifestyle changes, these possibilities are worth investigating.
Positioning Can Make a Real Difference
The angle between your rectum and anal canal changes depending on how you sit. On a standard toilet, that angle sits around 100 degrees, creating a bend that requires more straining to push past. In a full squat, the angle opens to about 126 degrees, straightening the pathway. Research confirms that squatting also requires less abdominal pressure to defecate.
You can approximate this by placing a footstool under your feet while sitting on the toilet, raising your knees above hip level. Leaning forward slightly with your elbows on your knees gets you even closer to the optimal angle. It’s a simple change, but for people who strain regularly, it can make an immediate difference.
When Constipation Signals Something Serious
Most constipation is uncomfortable but not dangerous. It becomes an emergency if you haven’t had a bowel movement for a prolonged period and you’re also experiencing severe abdominal pain or major bloating, which could indicate a bowel obstruction. Other warning signs that need prompt attention: vomiting alongside constipation, blood in your stool, or unexplained weight loss. These don’t necessarily mean something dire, but they do need evaluation to rule out conditions like colorectal cancer or inflammatory bowel disease.