What causes constipation, and why do some people get it more than others?

What it is

Constipation is a symptom picture rather than a single disease. The Rome IV criteria define functional constipation by symptoms - infrequent stools, hard or lumpy stools, straining, a feeling of incomplete evacuation and the need for digital assistance - present for at least a quarter of bowel movements over months, not days. Reviews separate primary (functional) constipation, which is classified by colonic transit and anorectal function into normal transit, slow transit and defecatory or pelvic floor disorders, from secondary constipation caused by a medicine or another condition.

What the research says

The evidence is strongest for the definition and for who is affected: pooled prevalence of functional constipation by Rome IV criteria is about 10% of adults, roughly twice as common in women, about a third of pregnancies, and clearly higher with age, diabetes, stroke with paralysis, Parkinson's disease and opioid use. The evidence for individual lifestyle causes is much weaker and mostly observational: higher physical activity is associated with lower risk in cohort studies, while the claim that drinking more water fixes constipation in people who are not dehydrated is not supported. Government bodies list travel, routine change, ignoring the urge to go, pregnancy and ageing as causes; those are positions built on clinical experience rather than trials.

Evidence grade: Well established.

What goes wrong

A review of laxative safety reports that chronic constipation itself has been linked to colon cancer risk, though it treats this as a reported possibility rather than an established effect. (Source 1)

• Expert review, not systematic, Very low certainty.
• Size: not applicable - critical narrative review of existing studies.
• Who: people with chronic constipation.
• How long: long term, not quantified.
• Result: no effect size reported for the constipation-cancer link; the review says many studies of laxative harm failed to adjust for neurological disease, metabolic disorders and age.
• Funding: not stated in the text we read.

chronic constipation itself has been reported to potentially increase the risk of colon cancer

What the evidence supports

Rome IV defines functional constipation by a cluster of symptoms, not by stool frequency alone. (Source 2)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - expert review for the American Gastroenterological Association.
• Who: adults with chronic constipation.
• How long: not applicable.
• Result: requires 2 or more of the listed symptoms affecting more than 25% of bowel movements for at least 6 months, with active symptoms in the past 3 months.
• Funding: not stated.

The Rome IV criteria are predominantly symptom-based and as such require that patients with a diagnosis of FC have 2 or more of these symptoms, which affect >25% of bowel movements for at least 6 months and active symptoms for the past 3 months.

The symptoms patients actually report include straining, incomplete evacuation and hard or lumpy stools, not only fewer than three bowel movements a week. (Source 2)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - expert review.
• Who: adults with chronic constipation.
• How long: not applicable.
• Result: fewer than 3 bowel movements per week is one component; straining, incomplete evacuation, digital assistance, bloating and hard or lumpy stools are described as more important.
• Funding: not stated.

Patients with constipation have infrequent stools (fewer than 3 bowel movements per week) and, more importantly, straining at stool, a feeling of incomplete evacuation, a need for digital assistance to evacuate stool, bloating, and hard or lumpy stools.

Primary constipation is classified into three mechanisms - normal transit, slow transit and pelvic floor dysfunction or defecatory disorders - on the basis of colonic transit and anorectal function tests. (Source 3)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - expert review.
• Who: adults with chronic constipation.
• How long: not applicable.
• Result: three classifications: normal transit constipation, slow transit constipation and pelvic floor dysfunction or defecatory disorders.
• Funding: not stated.

the classifications are normal transit constipation (NTC), slow transit constipation (STC), and pelvic floor dysfunction or DDs

Functional constipation affects about one adult in ten when Rome IV criteria are used, and is about twice as common in women. (Source 4)

• Meta-analysis, Low certainty.
• Size: 275,260 participants across 45 studies and 80 populations.
• Who: general adult populations worldwide.
• How long: cross-sectional surveys.
• Result: pooled prevalence 10.1% (95% CI 8.7-11.6) with Rome IV; odds ratio for women 2.40 (95% CI 2.02-2.86) with Rome I, 1.94 (1.46-2.57) Rome II, 2.32 (1.85-2.92) Rome III; I-squared 98.2% for Rome IV.
• Funding: funding stated as None.

and 10·1% (8·7–11·6; I 2 =98·2%) when Rome IV criteria were used. Prevalence of functional constipation was higher in women, irrespective of the Rome criteria used

Constipation is common in pregnancy, with about a third of pregnancies affected across pooled studies. (Source 5)

• Meta-analysis, Low certainty.
• Size: 13 studies.
• Who: pregnant women.
• How long: across all three trimesters.
• Result: pooled global prevalence 32.4% overall; 21.1% first trimester, 34% second trimester, 30.3% third trimester.
• Funding: Deputy for Research and Technology, Kermanshah University of Medical Sciences.

The results show that the global prevalence of constipation throughout pregnancy is 32.4%, with the first trimester at 21.1%, the second trimester at 34%, and the third trimester at 30.3%.

Constipation is associated with Parkinson's disease, and is reported more often in the prodromal stage than in controls. (Source 6)

• Meta-analysis, Low certainty.
• Size: not stated in the abstract passage; pooled across studies with I-squared 90%.
• Who: people with Parkinson's disease and controls.
• How long: varied by study design and disease duration.
• Result: pooled OR 2.36 (95% CI 1.93-2.88), I-squared 90%, p < 0.01; prevalence 20% in prodromal PD versus 11% in controls (p < 0.01)
• Funding: not stated.

The pooled OR for the association between constipation and PD was 2.36 (95% confidence interval: 1.93–2.88), although strong heterogeneity was observed (I2 = 90%, p < 0.01).

Among patients attending a single Japanese centre for colonoscopy, diabetes, chronic renal failure, stroke with paralysis, older age, female sex and several medicines were independently associated with constipation symptoms. (Source 7)

• Survey study, Low certainty.
• Size: 8,621 patients undergoing colonoscopy.
• Who: patients undergoing colonoscopy at a single Japanese centre - a clinic population selected for bowel investigation, not a general-population sample.
• How long: single time point survey.
• Result: constipation symptoms in 33.3% of this colonoscopy cohort, which is a figure for people attending for colonoscopy and not a general-population prevalence; diabetes OR 1.4 (p<0.001), chronic renal failure OR 2.6 (p<0.001), cerebral stroke with paralysis OR 1.7 (p=0.009), opioid use OR 2.1 (p=0.002), antiparkinsonian medication OR 1.9 (p=0.030), benzodiazepine OR 1.7 (p<0.001); IBS predicted refractory symptoms OR 3.1 (p<0.001)
• Funding: not stated.

chronic renal failure (OR 2.6, p < 0.001), ischemic heart disease (OR 1.3, p = 0.008), diabetes (OR 1.4, p < 0.001)

Across 13 cohort studies, higher physical activity was associated with a lower risk of constipation; this is an association rather than proof of cause, and the paper's headline confidence interval is printed in a form that cannot be correct. (Source 8)

• Systematic review, Low certainty.
• Size: 119,426 participants and 63,713 cases across 13 cohort studies.
• Who: adults in community cohorts, with subgroups by region and sex.
• How long: cohort follow-up, durations not stated in the abstract.
• Result: higher versus lower physical activity RR=0.69, with the paper printing its interval as "95% CI=0.88-0.83", which is impossible as printed; moderate versus lower activity RR=0.87 (95% CI=0.79-0.95); adherence to international activity guidelines RR=0.87 (95% CI=0.81-0.93); men and women collectively RR=0.66 (95% CI=0.55-0.80), described as a 34% lower risk.
• Funding: National Natural Science Foundation of China (82374610 and 82105038)

Limit of this finding: The paper prints the headline comparison as "RR=0.69; 95% CI=0.88-0.83". That interval cannot be right as printed: the lower figure is larger than the upper one, and 0.69 does not lie between them. This is an error in the published paper, not in our transcription. Read it as showing the direction of the association only - lower constipation risk in more active people - and do not treat 0.69 or that interval as a reliable size of effect. The paper's other intervals, such as RR=0.87 (95% CI=0.81-0.93) for meeting international activity guidelines, are internally consistent.

The results indicated that higher levels of PA were associated with a decreased risk of constipation compared with lower levels of PA

A United States government body lists pregnancy, ageing, travel, ignoring the urge to go and changes in medicines or diet among the causes of constipation. (Source 9)

• Official position, Certainty not rated.
• Size: not applicable - agency health information page.
• Who: general public.
• How long: current at the date of the page.
• Result: no effect size given; causes listed include pelvic floor disorders and colon surgery, irritable bowel syndrome, and life or routine changes.
• Funding: United States government agency.

Constipation can happen when your life or daily routine changes.

The same body lists the conditions it regards as causes of secondary constipation, including hypothyroidism, diabetes, neurological disease, spinal cord or brain injury and intestinal obstruction. (Source 10)

• Official position, Certainty not rated.
• Size: not applicable - agency health information page.
• Who: general public.
• How long: current at the date of the page.
• Result: no effect size given; conditions listed include celiac disease, disorders of brain and spine such as Parkinson's disease, spinal cord or brain injuries, diabetes, hypothyroidism, diverticular disease or proctitis, obstruction and anatomic problems.
• Funding: United States government agency.

conditions that affect your hormones, such as hypothyroidism

Clinical reviews list alarm features in a constipated patient that they say warrant endoscopic evaluation. (Source 11)

• Expert review, not systematic, Certainty not rated.
• Size: not applicable - clinical review.
• Who: adults presenting with chronic constipation.
• How long: not applicable.
• Result: red flags listed as hematochezia, unintended weight loss of 10 lb (4.5 kg) or more, family history of colon cancer, iron deficiency anaemia, positive faecal occult blood test, or acute onset in an older patient.
• Funding: not stated.

Physicians should also be alert for red flags, such as hematochezia, unintended weight loss of 10 lb (4.5 kg) or more, a family history of colon cancer, iron deficiency anemia, positive fecal occult blood tests, or acute onset of constipation in an older patient.

A US government body states the symptoms that should prompt urgent medical attention alongside constipation. (Source 12)

• Official position, Certainty not rated.
• Size: not applicable - agency health information page.
• Who: general public.
• How long: current at the date of the page.
• Result: no effect size; listed features are rectal bleeding, blood in stool, constant abdominal pain, inability to pass gas, vomiting, fever, lower back pain and unintentional weight loss, plus family history of colon or rectal cancer.
• Funding: United States government agency.

You should see a doctor if your symptoms do not go away with self-care or you have a family history of colon or rectal cancer.

Medicines are among the causes a government body lists, which matters when a tracker has to flag what someone is taking. (Source 10)

• Official position, Certainty not rated.
• Size: not applicable - agency health information page.
• Who: general public.
• How long: current at the date of the page.
• Result: no rates given; the list names aluminium- and calcium-containing antacids, anticholinergics and antispasmodics, anticonvulsants, calcium channel blockers, diuretics, iron supplements, Parkinson's medicines, narcotic pain medicines and some antidepressants.
• Funding: United States government agency.

Medicines and dietary supplements that can make constipation worse include

What the evidence does not support

Drinking more water than public health recommendations has not been shown to improve constipation, which weakens the common claim that low fluid intake is a general cause. (Source 13)

• Expert review, not systematic, Low certainty.
• Size: one RCT in 141 people is the trial evidence cited for water supplementation.
• Who: people with chronic constipation.
• How long: trial not stated beyond the comparison described.
• Result: the review's water-supplementation paragraph reports one RCT in 141 people given 2 l/day versus ad libitum 1.1 l/day, both on a 25 g/day fibre diet, with 4.2 (sd 1.3) versus 3.3 (sd 1.8) bowel movements per week, P < 0.001, and the same paragraph closes by stating there is no evidence that increasing total water intake beyond public health recommendations improves constipation outcomes.
• Funding: author declares education and research grants from Alpro, Almond Board of California, International Nut and Dried Fruit Council and Nestec, and consultancy for Puratos and Danone.

There is however no evidence suggesting that increasing total water intake beyond public health recommendations improves constipation outcomes.

Where the research disagrees

Whether increasing fluid intake is a cause of, and a fix for, constipation in people who are not dehydrated

• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), United States, page read 2026-09-23, position: not drinking enough liquids, or dehydration (Source 10)
• Dimidi, Proceedings of the Nutrition Society 2025, narrative-review of trial evidence: There is however no evidence suggesting that increasing total water intake beyond public health recommendations improves constipation outcomes. (Source 13)

A common belief, and what the research shows

The belief: Constipation means going less than once a day, and it is caused by not drinking enough water.

What the research shows: The clinical definition is not about a daily bowel movement: the Rome IV criteria need two or more symptoms affecting more than a quarter of bowel movements over months, and reviews say that beyond frequency, "straining at stool, a feeling of incomplete evacuation, a need for digital assistance to evacuate stool, bloating, and hard or lumpy stools" matter more. On fluid, a 2025 review of the trial evidence states plainly that "There is however no evidence suggesting that increasing total water intake beyond public health recommendations improves constipation outcomes."

Questions and answers

What is constipation, exactly - is it just not going every day?

No. Clinically it is a pattern of symptoms rather than a missed day. The Rome IV criteria, which reviews for the American Gastroenterological Association describe, need two or more symptoms - hard or lumpy stools, straining, incomplete evacuation, needing to help with a finger, blockage, or fewer than three bowel movements a week - affecting more than a quarter of bowel movements, present for months. Stool form and straining carry as much weight as frequency. (Source 2)

What is actually going on in my body when I am constipated?

Reviews describe three different mechanisms. In normal transit constipation stool moves through the colon at a normal speed but the person still has symptoms; in slow transit constipation the colon moves stool too slowly; in a defecatory or pelvic floor disorder the muscles of the pelvic floor and anus do not coordinate to let stool out. Which one a person has is worked out with colonic transit and anorectal function tests, not from symptoms alone. (Source 3)

Is being constipated actually harmful, or just uncomfortable?

The literature treats it as a symptom that is usually benign but sometimes signals something serious, and one that can be hard to shift. In a study of 8,621 people attending for colonoscopy - a clinic group, not a general population sample - a third had constipation symptoms and 61.4% of those already taking something for it still had refractory symptoms. A review of laxative safety notes that chronic constipation itself has been reported as a possible colon cancer risk factor, which is a reported association rather than an established effect. Memios does not diagnose and does not give medical advice. (Source 7)

What makes constipation more likely?

Pooled and single-study evidence points to being female, older age, pregnancy, diabetes, chronic kidney failure, stroke with paralysis, Parkinson's disease, irritable bowel syndrome, and several medicine groups - opioids, antiparkinsonian drugs and benzodiazepines among them. Government bodies add travel, routine change, ignoring the urge, and changes in what you eat. Most of this is observational, so it shows what travels with constipation rather than proving cause. (Source 7)

If something I am doing or taking is causing it, what reduces it?

Where a medicine is the cause, the literature on drug-induced constipation is about the drug, its dose and its alternatives - for example hospital data show the risk of severe constipation differs between opioids and rises with daily dose. Where inactivity is part of the picture, cohort studies associate higher physical activity with lower risk. This is a report of what studies found, not advice about your own medicines. (Source 14)

Why do some people get constipated and others do not?

Prevalence work shows it clusters: about 10% of adults by Rome IV criteria, about twice as often in women, and much more in pregnancy at roughly a third. It rises with age and with conditions that affect nerves, hormones, metabolism or the bowel wall, and with medicines that slow the gut. The same reviews report large unexplained differences between countries even when identical criteria are used. (Source 4)

Which foods and drinks are linked to constipation?

The dietary signal in the literature is mostly about what is missing rather than what is eaten: a US government body lists not eating enough fibre and not drinking enough liquids among causes. On the trial side, fibre supplements raise response rates and stool frequency, with psyllium the most consistent, while polydextrose and galacto-oligosaccharides did not improve outcomes. There is no evidence that drinking more water than public health recommendations helps someone who is not dehydrated. (Source 10)

What happens if constipation is just left alone?

The literature does not give a single answer, and long-term natural history studies are thin. What it does say is that symptoms often persist despite treatment - 61.4% of treated people in one large study still had refractory symptoms - and that certain features alongside constipation are treated as reasons for prompt investigation rather than watchful waiting. (Source 12)

How is constipation tested for, and how good are those tests?

There is no blood test for constipation itself. Diagnosis is symptom-based using the Rome IV criteria, and the subtype is worked out with colonic transit studies and anorectal function testing. Clinical reviews say endoscopy is used when alarm features are present, to look for malignancy rather than to diagnose constipation. (Source 11)

What counts as a red flag that means I should see a clinician?

Both a clinical review and a US government body name the same short list: rectal bleeding or blood in the stool, unintentional weight loss, iron deficiency anaemia or a positive faecal occult blood test, a family history of colon or rectal cancer, and new or sudden onset of constipation in an older person. The government page adds constant abdominal pain, inability to pass gas, vomiting, fever and lower back pain as reasons to be seen right away. Memios reports these as recorded positions and does not diagnose. (Source 12)

What is the difference between primary and secondary constipation?

Primary, or functional, constipation is defined by symptoms with no other disease driving it, and is subdivided by how fast the colon moves stool and how well the pelvic floor coordinates. Secondary constipation is caused by something identifiable - a medicine, or a condition such as hypothyroidism, diabetes, Parkinson's disease, spinal cord injury or an obstruction. A US government body lists those conditions explicitly. (Source 10)

Does being pregnant or getting older make constipation more likely?

For pregnancy, a meta-analysis of 13 studies put the global prevalence at 32.4% across pregnancy, highest in the second trimester at 34%. For age, a cross-sectional study of 8,621 people found older age independently associated with constipation symptoms (OR 1.3, p < 0.001), and a US government body lists getting older among the routine changes that alter bowel habit. (Source 5)

Is it true that not drinking enough water causes constipation?

A government body lists not drinking enough liquids, or dehydration, among causes. A 2025 review of the trial evidence is more cautious: a single RCT in 141 people found that 2 litres a day of water on a 25 g fibre diet raised stool frequency compared with about 1.1 litres, but the review states there is no evidence that increasing total water intake beyond public health recommendations improves constipation outcomes. (Source 13)

References

1. Therapeutic Advances in Gastroenterology. Review article: do stimulant laxatives damage the gut? A critical analysis of current knowledge. 2024. PMID 38887508, DOI 10.1177/17562848241249664. Read the source
2. Gastroenterology. Mechanisms, Evaluation, and Management of Chronic Constipation. 2020. PMID 31945360, DOI 10.1053/j.gastro.2019.12.034. Read the source
3. Gastroenterology. Mechanisms, Evaluation, and Management of Chronic Constipation. 2020. PMID 31945360, DOI 10.1053/j.gastro.2019.12.034. Read the source
4. The Lancet Gastroenterology & Hepatology. Global prevalence of functional constipation according to the Rome criteria: a systematic review and meta-analysis. 2021. PMID 34090581, DOI 10.1016/S2468-1253(21)00111-4. Read the source
5. BMC Pregnancy and Childbirth. Global prevalence of constipation during pregnancy: a systematic review and meta-analysis. 2024. PMID 39707279, DOI 10.1186/s12884-024-07057-y. Read the source
6. European Neurology. Constipation in Parkinson's Disease: A Systematic Review and Meta-Analysis. 2023. PMID 36470230, DOI 10.1159/000527513. Read the source
7. Digestion. Prevalence and Risk Factors of Constipation Symptoms among Patients Undergoing Colonoscopy: A Single-Center Cross-Sectional Study. 2024. PMID 38754395, DOI 10.1159/000539366. Read the source
8. Journal of Global Health. Physical activity and constipation: A systematic review of cohort studies. 2024. DOI 10.7189/jogh.14.04197. Read the source
9. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health. Symptoms & Causes of Constipation. 2026. Read the source
10. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health. Symptoms & Causes of Constipation. 2026. Read the source
11. American Family Physician. Diagnostic Approach to Chronic Constipation in Adults. 2011. Read the source
12. National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health. Symptoms & Causes of Constipation. 2026. Read the source
13. Proceedings of the Nutrition Society. Dietary management of chronic constipation: a review of evidence-based strategies and clinical guidelines. 2025. DOI 10.1017/S0029665125100694. Read the source
14. BMC Medicine. Comparative risk of severe constipation in patients treated with opioids for non-cancer pain: a retrospective cohort study in Northwest England. 2025. PMID 40518524, DOI 10.1186/s12916-025-04118-7. Read the source