Causes of Constipation

The major identifiable causes of constipation are listed in below. Despite the many different possible causes of constipation, most cases seen in clinical practice are functional in origin, and they are often made worse by such factors as inadequate water or fiber intake, or the use of constipating medications. Many cases of constipation may in fact have several contributing factors.

“Functional” means the primary abnormality is in the way the body works.

Constipation can be broadly divided into 3 classes based upon the underlying physiologic cause;

  • normal-transit constipation,
  • slow transit constipation, and
  • pelvic floor dysfunction.

Normal-Transit Constipation (NTC)

In normal-transit constipation, colonic motility (the way muscles contract and relax to move contents through the colon) is unaltered. NTC, as its name implies, indicates that BMs move at a normal speed through the colon. However, patients with NTC may experience other difficulties in stool passage, such as harder stools. Most individuals with NTC have symptoms consistent with irritable bowel syndrome with constipation (IBS-C). 

Learn more about IBS

Slow-transit (STC)

STC, as its name implies, indicates that BMs move more slowly through the colon. This is caused by gut dysmotility. This form of constipation is often treated with fiber and laxatives. However, if this does not help, a healthcare provider can discuss other options for relief.

Pelvic floor dysfunction

The pelvic floor is a group of muscles that supports the organs within the pelvis and lower abdomen and also plays an important role in defecation. Persons with pelvic floor dysfunction have a functional outlet obstruction, a defect in the coordination necessary for stool evacuation. This usually occurs due to the failure of the pelvic floor muscles (including the anal sphincter) to relax appropriately during evacuation efforts. When this happens it makes stool passage much more difficult, regardless of whether stool transit in the colon is normal or delayed.

Dyssynergic Defecation:

In some cases, individuals contract their pelvic muscles instead of relaxing them. This condition is known variously as “dyssynergic defecation,” “pelvic floor dyssynergia,” “paradoxical pelvic floor/puborectalis contraction,” or “anismus.”

Dyssynergic defecation is a common cause of chronic constipation – but one that is often unrecognized. Find out more by clicking the image below to watch short videos about dyssynergic defecation.

cause of constipation

The majority of persons seen by a doctor have normal-transit constipation, followed by pelvic floor dysfunction, and slow-transit constipation.

As noted, some patients can have a combination of slow transit and pelvic floor dysfunction (functional outlet obstruction).

Medical Conditions Associated with the Development of Chronic Constipation

Potential Secondary Causes Examples
Mechanical ObstructionStrictures, Inflammation, Tumors, External compression
Endocrine/Metabolic DisordersDiabetes, Hypothyroidism, Hyper/Hypocalcemia, Hypokalemia, Hypomagnesemia, Cystic Fibrosis, Uremia, Heavy Metal Poisoning
Neuropathies/MyopathiesScleroderma, Parkinson’s Disease, ALS, Stroke, Spinal Cord injuries or congenital defects, Multiple Sclerosis, Dysautonomia
Pregnancy

Medications Associated with Constipation

Note: Many medications list constipation as a side effect and not all are listed here. Be sure to tell your doctor about any drugs or supplements being taken, both prescription and over-the-counter.

Medications Associated with the Development of Chronic Constipation*:

Prescription Drug FamilyCommon UsageExamples
Opioids (narcotics)Pain reliefHydrocodone, Oxycodone,
Fentanyl, Morphine, Codeine
AnticholinergicsRelief of muscle spasms/cramps of
the bowel/bladder
Hyoscyamine, Dicyclomine, Belladonna
Tricyclic antidepressantsDepression/Functional Bowel DisordersAmitriptyline, Imipramine
AntihypertensivesReduce Blood Pressure, Betablockers, Calcium channel blockers, ACE inhibitorsMetoprolol, Nifedipine,
Enalapril
DiureticsReduce fluid retentionFurosemide, Bumetanide
Bile acid sequestrantReduce cholesterolCholestyramine, Colestipol
AnticonvulsantsReduce potential for seizuresPhenytoin, Valproic Acid
*This list is NOT all-inclusive. It represents common categories of drugs known to cause constipation. Other families of drugs and drugs within these families may also cause constipation. Some categories include both prescription and non-prescription treatments. If you are concerned that a medication you are taking may be causing constipation, please consult your healthcare provider, pharmacist, or the medication’s package insert.
Non-prescription DrugsCommon UsageExamples
Antacids (calcium &
aluminum containing)
Relieve heartburn and stomach discomfortMaalox, Mylanta, Gaviscon,
Tums, Rolaids
Iron supplements Iron deficiency anemiaIron sulfate
Calcium supplementsCalcium deficiency Calcium carbonate, Calcium citrate
Antidiarrheal agentsreduce diarrheaLoperamide, Bismuth
Nonsteroidal anti-inflammatory agents (NSAIDs)Reduce inflammationAspirin, Ibuprofen, Naproxen, Diclofenac, Meloxicam
AntihistaminesControl allergiesDiphenhydramine
*This list is NOT all-inclusive. It represents common categories of drugs known to cause constipation. Other families of drugs and drugs within these families may also cause constipation. Some categories include both prescription and non-prescription treatments. If you are concerned that a medication you are taking may be causing constipation, please consult your healthcare provider, pharmacist, or the medication’s package insert.

Adapted from IFFGD Publication: Chronic Constipation: From Evaluation to Treatment by Robert D. Madoff, MD, FACS, Division of Colon and Rectal Surgery, University of Minnesota, Minneapolis, MN.

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