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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)

Normal Transit Constipation (NTC), as its name implies, indicates that bowel movements move at a normal speed through the colon. Most individuals with NTC have symptoms consistent with irritable bowel
syndrome with constipation (IBS-C). 

Learn more about IBS

Slow-transit (STC)

Slow Transit Constipation (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.

Functional Defecation Disorders

Evacuation disorders are causes of constipation linked to the pelvic floor, a group of muscles supporting the organs in the lower part of the abdomen, located between the hip bones. These muscles help bowel movements. Anatomical (or structural) abnormalities in the pelvic floor can affect your bowel movements. Some people are born with such abnormalities; others experience them after changes to the pelvic floor, such as surgery. However, functional defecation disorders (FDDs) are the most common form of evacuation ailment.

FDDs occur when the colon’s muscles do not appropriately allow the passage of BMs out of the last part of the colon. In many instances, this causes dyssynergic defecation (DD)—an inability to relax your pelvic floor muscles to have a BM and/or spasms in the pelvic floor muscles which lead to difficulty passing BMs. Imagine there is a closed door at the bottom of the colon: when we receive the urge to have a BM and bear down or push to have a BM, the muscles in the pelvic floor should relax so that the door opens to allow the BMs to pass. With FDDs, however, the door does not open enough or tightens even further. It is important to identify this condition early because the treatment is different than the treatments for NTC and STC.

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).

Secondary Constipation: Causes associated with another condition or medication

Secondary implies that the constipation is caused by, or associated with, another medical condition or use of a medication known to cause constipation. 

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: Constipation Overview by Darren Brenner , M.D., AGAF, FACG, Associate Professor and Director of the Neurogastromotility Program, Division of Gastroenterology, Northwestern University Feinberg School of Medicine, Chicago, IL

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