What Causes Constipation — and Why It Keeps Coming Back

What are the most common reasons for constipation?

For most people, constipation traces to lifestyle factors 1Ref 1Chang L, Chey WD, Imdad A, et al. (2023).American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.Opioids as a leading cause of medication-induced constipation; dietary fiber and fluid intake as primary lifestyle factors; pelvic floor dysfunction as an underdiagnosed cause; stimulant laxative overuse; breaking the chronic constipation cycle2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2018).Constipation.Calcium channel blockers, anticholinergics, and iron supplements as constipating medications; diabetes and autonomic neuropathy as causes; guidance on when not to stop medications without clinician input:

Low fiber intake. Fiber draws water into stool and adds bulk, keeping it soft and moving through the colon efficiently. A diet low in fruits, vegetables, and whole grains produces stools that move more slowly and become harder.

Inadequate fluid intake. When the body is short on fluids, the colon absorbs extra water from stool, making it dry and difficult to pass.

Inactivity. Physical movement stimulates gut motility; prolonged inactivity tends to slow it.

Disrupted routine. Travel, stress, or schedule changes can slow the bowel because the gut is sensitive to the nervous system and routine.

Which medications commonly cause constipation?

Medication is one of the most underrecognized causes. Opioid pain medications slow gut motility significantly and are a leading cause of medication-induced constipation 1Ref 1Chang L, Chey WD, Imdad A, et al. (2023).American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.Opioids as a leading cause of medication-induced constipation; dietary fiber and fluid intake as primary lifestyle factors; pelvic floor dysfunction as an underdiagnosed cause; stimulant laxative overuse; breaking the chronic constipation cycle. Other frequent contributors include:

• Iron supplements
• Certain antacids containing aluminum or calcium
• Some blood pressure medications (calcium channel blockers)
• Anticholinergic medications (some bladder drugs, antihistamines, certain antidepressants)

If constipation started or worsened around the time a medication was added or the dose changed, mention this to your clinician. Never stop a prescribed medication without guidance, but flagging it as a side effect is appropriate 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2018).Constipation.Calcium channel blockers, anticholinergics, and iron supplements as constipating medications; diabetes and autonomic neuropathy as causes; guidance on when not to stop medications without clinician input.

What health conditions can cause constipation?

Several conditions slow the bowel:

Hypothyroidism (underactive thyroid). A low thyroid slows nearly every body process, including gut motility 3Ref 3Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Hypothyroidism as a cause of constipation through slowed gut motility, alongside fatigue, cold intolerance, and weight gain. Fatigue, feeling cold, weight gain, dry skin, and hair changes alongside constipation suggest thyroid testing is worthwhile.

Irritable bowel syndrome with constipation (IBS-C). A functional gut disorder where the bowel is structurally normal but moves sluggishly or irregularly, often with bloating and cramping that ease after a bowel movement 4Ref 4Lacy BE, Pimentel M, Brenner DM, Chey WD, Keefer LA, Long MD, Moshiree B (2021).ACG Clinical Guideline: Management of Irritable Bowel Syndrome.IBS-C as a functional cause of chronic constipation with abdominal cramping relieved by bowel movement and associated bloating.

Diabetes. Long-standing diabetes can cause autonomic neuropathy — nerve damage affecting involuntary functions including gut movement 2Ref 2National Institute of Diabetes and Digestive and Kidney Diseases (2018).Constipation.Calcium channel blockers, anticholinergics, and iron supplements as constipating medications; diabetes and autonomic neuropathy as causes; guidance on when not to stop medications without clinician input.

Pelvic floor dysfunction. Difficulty coordinating the muscles needed to pass stool is underdiagnosed, particularly in women with a history of vaginal childbirth or pelvic surgery. People with this condition often describe straining, incomplete emptying, or needing to press on the perineum to complete a bowel movement 1Ref 1Chang L, Chey WD, Imdad A, et al. (2023).American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.Opioids as a leading cause of medication-induced constipation; dietary fiber and fluid intake as primary lifestyle factors; pelvic floor dysfunction as an underdiagnosed cause; stimulant laxative overuse; breaking the chronic constipation cycle.

Structural causes. Less commonly, colorectal narrowing, polyps, or cancer can cause constipation — which is why new-onset constipation after age 45 to 50 deserves evaluation 5Ref 5Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.New-onset constipation after age 45 to 50 as a reason for colonoscopy to rule out structural causes including colorectal cancer.

Why does constipation become chronic?

Constipation can become self-reinforcing. Straining leads to painful hemorrhoids or anal fissures, which cause people to avoid the urge to defecate, which worsens constipation 6Ref 6Wald A, Bharucha AE, Limketkai B, Malcolm A, Remes-Troche JM, Whitehead WE, Zutshi M (2021).ACG Clinical Guidelines: Management of Benign Anorectal Disorders.Straining leading to hemorrhoids and fissures, creating a self-reinforcing cycle of constipation avoidance. Repeatedly suppressing the urge over time can reduce the bowel's responsiveness. Overuse of stimulant laxatives may reduce the colon's natural ability to contract. Breaking the cycle usually means addressing the root cause, not just managing symptoms 1Ref 1Chang L, Chey WD, Imdad A, et al. (2023).American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.Opioids as a leading cause of medication-induced constipation; dietary fiber and fluid intake as primary lifestyle factors; pelvic floor dysfunction as an underdiagnosed cause; stimulant laxative overuse; breaking the chronic constipation cycle.

When should you see a clinician about constipation?

Contact a clinician if:

• Constipation is new and has persisted more than three weeks without a clear cause
• You notice blood in the stool or unexplained weight loss
• You are over 45 to 50 and have a new pattern of constipation 5Ref 5Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.New-onset constipation after age 45 to 50 as a reason for colonoscopy to rule out structural causes including colorectal cancer
• Dietary changes and increased fluid intake have not helped
• You suspect a medication is responsible
• You have symptoms that suggest hypothyroidism, pelvic floor dysfunction, or IBS 3Ref 3Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Hypothyroidism as a cause of constipation through slowed gut motility, alongside fatigue, cold intolerance, and weight gain4Ref 4Lacy BE, Pimentel M, Brenner DM, Chey WD, Keefer LA, Long MD, Moshiree B (2021).ACG Clinical Guideline: Management of Irritable Bowel Syndrome.IBS-C as a functional cause of chronic constipation with abdominal cramping relieved by bowel movement and associated bloating

A clinician can check thyroid function, review medications, and decide whether a colonoscopy is warranted 5Ref 5Shaukat A, Kahi CJ, Burke CA, Rabeneck L, Sauer BG, Rex DK (2021).ACG Clinical Guidelines: Colorectal Cancer Screening 2021.New-onset constipation after age 45 to 50 as a reason for colonoscopy to rule out structural causes including colorectal cancer. Referral to a pelvic floor physical therapist or gastroenterologist is available when first-line approaches are not sufficient 1Ref 1Chang L, Chey WD, Imdad A, et al. (2023).American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation.Opioids as a leading cause of medication-induced constipation; dietary fiber and fluid intake as primary lifestyle factors; pelvic floor dysfunction as an underdiagnosed cause; stimulant laxative overuse; breaking the chronic constipation cycle.