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).
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.
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 Obstruction | Strictures, Inflammation, Tumors, External compression |
| Endocrine/Metabolic Disorders | Diabetes, Hypothyroidism, Hyper/Hypocalcemia, Hypokalemia, Hypomagnesemia, Cystic Fibrosis, Uremia, Heavy Metal Poisoning |
| Neuropathies/Myopathies | Scleroderma, 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 Family | Common Usage | Examples |
| Opioids (narcotics) | Pain relief | Hydrocodone, Oxycodone, Fentanyl, Morphine, Codeine |
| Anticholinergics | Relief of muscle spasms/cramps of the bowel/bladder | Hyoscyamine, Dicyclomine, Belladonna |
| Tricyclic antidepressants | Depression/Functional Bowel Disorders | Amitriptyline, Imipramine |
| Antihypertensives | Reduce Blood Pressure, Betablockers, Calcium channel blockers, ACE inhibitors | Metoprolol, Nifedipine, Enalapril |
| Diuretics | Reduce fluid retention | Furosemide, Bumetanide |
| Bile acid sequestrant | Reduce cholesterol | Cholestyramine, Colestipol |
| Anticonvulsants | Reduce potential for seizures | Phenytoin, Valproic Acid |
| Non-prescription Drugs | Common Usage | Examples |
| Antacids (calcium & aluminum containing) | Relieve heartburn and stomach discomfort | Maalox, Mylanta, Gaviscon, Tums, Rolaids |
| Iron supplements | Iron deficiency anemia | Iron sulfate |
| Calcium supplements | Calcium deficiency | Calcium carbonate, Calcium citrate |
| Antidiarrheal agents | reduce diarrhea | Loperamide, Bismuth |
| Nonsteroidal anti-inflammatory agents (NSAIDs) | Reduce inflammation | Aspirin, Ibuprofen, Naproxen, Diclofenac, Meloxicam |
| Antihistamines | Control allergies | Diphenhydramine |
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.
