4 Common Causes of Constipation Explained.

Our content is not intended nor recommended as a substitute for medical advice by your doctor. Use for informational purposes only.

Summary of the causes of constipation:

Cause of Constipation.
1. Chronic idiopathic Constipation.
Normal colonic transit
Slow transit constipation (colon inertia)
Dyssynergic defecation
2. Irritable Bowel Syndrome (IBS)
3. Drugs.
Analgesics (NSAIDs)
Iron supplements
Aluminum (antacids, sucralfate)
Ganglionic blockers
Vinca alkaloids
Calcium channel blockers
5HT3 antagonists
4-A. Neurogenic disorders
Peripheral (affecting the peripheral nerves)
Diabetes mellitus
Autonomic neuropathy
Hirschsprung disease
Chagas disease
Intestinal pseudoobstructionCentral (affecting the brain and the spinal cord):
Multiple sclerosis
Spinal cord injury
Parkinson disease
4-B. Non-neurogenic disorders
Anorexia nervosa
Systemic sclerosis
Myotonic dystrophy

1. Chronic idiopathic constipation (functional constipation).

Severe chronic idiopathic (functional) constipation is more common in females. However, we don’t fully understand why it is more common in women.

Unlike IBS constipation, there is little or no abdominal pain with functional constipation. However, functional constipation is less common than IBS-C.

In one study, IBS-C was responsible for 71% of the cases of chronic constipation; only 29% of the cases of chronic constipation were due to functional constipation (reference).

functional constipation vs ibs constiaption

Symptoms and characteristics of chronic idiopathic constipation:

  • More common in females.
  • Doesn’t improve on mild laxatives or fiber supplements.
  • No significant abdominal pain (unlike IBS-C).
  • Fewer than three bowel movements a week OR
  • Straining during bowel movements.
  • Passing lumpy or hard stool most of the time.
  • Feeling like something is blocking the passage of the poop.
  • The need for help to empty the rectum (using your fingers or pressing on your abdomen).

How does functional constipation occur?

We don’t fully understand the mechanism of functional constipation. However, Defecation studies helped us identify distinct types and mechanisms of chronic idiopathic constipation (reference).

  • Slow motility of the colon (slow transit constipation or colon inertia): occurs when your colon fails to move and propel the poop after eating. Researchers think it is due to defects in the nerves supplying the colon (myenteric nerve plexus).
  • Abnormal defecation (dyssynergic defecation): This occurs when your pelvic muscle and anal sphincters fail to relax or abnormally contract to prevent you from defecation. The colon motility is often normal in dyssynergic defecation (normal colon transit).
  • Abnormal feeling of defecation (Normal colon transit): colon motility and defecation process are expected in such a case. In such a case, psychological factors may play a role. The defect is in how your brain perceives defecation.

How can doctors diagnose you with functional constipation?

Your doctor often requires a thorough examination and evaluation of your medical history. Then, he will repeatedly need advanced tests to exclude organic causes of constipation. Examples of the investigations used to diagnose functional constipation:

  • Laboratory data such as complete blood count, thyroid function, and serum glucose exclude secondary causes of constipation.
  • Colonoscopy: If your age is >50 years with new-onset constipation, your doctor often will require a colonoscopy. Also, your doctor will perform a colonoscopy if you have alarm signs such as anemia, weight loss, blood in stool, or a family history of colorectal cancer.
  • X-ray on the abdomen in the erect position. Also, an X-ray with barium (contrast) helps diagnose the cause.
  • Radiopaque marker study: the measurement of the movement of a radiopaque substance through the gut.
  • Wireless motility capsule: a capsule that you swallow to measure your gut’s motility. It is safer than the radiopaque marker study but less expensive.
  • Defecography: detects the abnormalities in the function and the structure of the pelvic muscles and the anorectal area during defecation.
  • Anorectal manometry: measures the pressure of the anal sphincters at rest and during defecation.
  • Colon manometry: a particular device that measures the pressure inside the colon’s lumen.
  • Ballon Expulsion test: A balloon is passed into the rectum and filled with water (about 50 CC). Then, you will be asked to expel the balloon (as you defecate). Patients with functional constipation may have delayed expulsion of the balloon.
  • Rectal barostat test: a specific balloon connected to a computerized device is used to assess rectal tone, pressure, and rectal sensation.

2. Irritable bowel syndrome with constipation (IBS-C).

Irritable bowel syndrome is another cause of chronic constipation. Irritable bowel syndrome is a more common cause of chronic constipation than functional constipation.

IBS is a common disease affecting 10-15% of people worldwide (reference). IBS is a functional bowel disease, so the main feature of IBS is recurrent abdominal pain (at least one day per week).

IBS has four subtypes:

  • IBS with prominent diarrhea.
  • IBS with prominent constipation.
  • IBS with Mixed Bowel habits.
  • Unclassified IBS (no prominent change in bowel habits).

IBS constipation and mixed IBS may present with recurrent attacks of severe constipation. IBS is also a functional disease.

The exact mechanism of constipation in IBS is also still not understood. Therefore, we diagnose IBS on clinical criteria (no specific test diagnoses IBS).

The most widely used criteria are the ROME IV criteria for the diagnosis of functional bowel diseases:

1- Onset: 6 months
your abdominal pain started to occur for six months or longer. If you started experiencing abdominal pain for fewer than six months, it is probably not IBS.
2- frequency of symptoms:
At least one day per week for the last three months
3- The main symptom: abdominal pain
Abdominal pain occurs anywhere in your abdomen; no IBS without abdominal pain.
4- The abdominal pain must be associated with at least 2:
1- change in stool frequency: together with the onset of the abdominal pain, there may be diarrhea or constipation or alternating diarrhea and constipation.
 2- the pain is associated with defecation: which means that abdominal pain is relieved by defecation. Or increased during defecation.
 3- the pain is associated with a change in stool form (appearance): stool becomes harder or softer (even without diarrhea or constipation.

IBS constipation occurs when your stool becomes hard or your strain in more than 25% of the bowel movements.

3. Medications.

This is an important and significantly underestimated cause of constipation. Too many medications can lead to chronic constipation.

If you and your doctor fail to identify drugs as a cause of constipation,  you may continue to suffer constipation for years. Drug-induced constipation is simply curable only by removing the causative drug.

Moreover, many medications are widely used, especially if you are a poly-medicated patient. Revise your list of medications (especially antihypertensive and analgesic medications) for any of the below drugs:

Drugs That cause constipation.Analgesics (NSAIDs)
Iron supplements
Aluminum (antacids, sucralfate)
Ganglionic blockers
Vinca alkaloids
Calcium channel blockers
5HT3 antagonists

4. Neurogenic diseases:

Your nervous system regulates your colon motility. Therefore, nervous system diseases are one of the commonest causes of constipation. Common neurogenic disorders that cause constipation include:

  • Diabetes mellitus: long-term uncontrolled diabetes destroys the nerves supplying your gut. Constipation is one of the common complications of diabetes mellitus.
  • Autonomic neuropathy: the autonomic nerves are nerves that control involuntary body activities such as heartbeats and the motility of your digestive system. Any damage to the autonomic nerves can lead to constipation.
  • The hirschsprung disease develops in childhood due to the failure to develop the sets of nerves responsible for colon motility. This leads to severe constipation and extreme colon dilation (congenital megacolon).
  • Multiple sclerosis (MS): a disease of unknown cause affecting any part of your nervous system causing damage to the brain, spinal cord, and other nerves.
  • Parkinson’s disease: Parkinson’s disease is common in older ages. It causes certain types of nerve cells inside your brain. It causes progressive tremors and limb rigidity. About 40-50% of patients with Parkinson’s disease have chronic constipation (reference).
  • Spinal cord injuries: by trauma, tumors, or operations.
  • Other less common diseases such as Chaga’s disease and intestinal pseudoobstruction.

5. Non-neurogenic diseases.

  • Hypothyroidism: decreased function of the thyroid gland.
  • Hypokalemia: decreased body levels of potassium
  • Pregnancy: pregnancy itself is a risk factor for constipation. About one in every four pregnant women experiences constipation (reference).
  • Anorexia Nervosa: a psychological eating disorder with complete loss of appetite, weight loss, and constipation.
  • Panhypopituitarism: decreased function of the pituitary gland. The pituitary gland is a small structure inside your brain that regulates most of your endocrinal system activity.
  • System sclerosis (scleroderma):  an autoimmune disease that causes fibrosis of the skin and internal organs (including your gut). Constipation affects 65% of patients with systemic sclerosis (reference).

6. Other risk factors for constipation.

  • Dehydration: Failing to drink enough water or losing fluids (as with vomiting) leads to constipation.
  • Older ages: 24-50% of older adults suffer from occasional or chronic constipation (reference1, reference2).
  • Being a female.
  • Low fiber diet: fibers form a build that helps stimulate colon motility and fights constipation. A low-fiber diet is a risk factor for constipation.
  • Lack of physical activity (reference).
  • Decreased overall caloric intake: this is a significant risk factor for constipation in the elderly (reference).
  • Depression (reference).
  • Having multiple diseases (such as diabetes, hypertension, etc.) simultaneously or taking various medications.