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).
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.
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 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: 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
