Functional Constipation

What is functional constipation?

Functional constipation is a disorder of gut-brain interaction characterized by persistently difficult, infrequent, or incomplete defecation that cannot be explained by a structural abnormality (like a tumor or stricture) or other medical condition. It is a very common problem, affecting up to 20% of adults in North America. The diagnosis is based on specific symptom criteria, known as the Rome IV criteria, and requires at least two of the following for the last 3 months: straining, lumpy or hard stools, a sensation of incomplete evacuation, a sensation of blockage, the need for manual maneuvers to pass stool, and/or fewer than three bowel movements per week.

Functional constipation is broadly divided into two main subtypes, which can overlap:

• Slow-Transit Constipation (STC): This is a disorder of colonic motility, where the colon contracts poorly and stool moves through it very slowly, leading to infrequent and hard stools.
• Functional Outlet Obstruction (Obstructed Defecation): This is a disorder of the pelvic floor and anorectal muscles. The colon transit may be normal, but the patient is unable to effectively coordinate the muscles needed to evacuate stool from the rectum. This includes conditions like dyssynergic defecation, where the pelvic floor muscles paradoxically contract instead of relaxing during attempted defecation.

Common Symptoms

The symptoms of functional constipation can be broad and vary between individuals. Common complaints include:

• Infrequent bowel movements: Having fewer than three bowel movements per week.
• Hard, lumpy stools: Stools that are difficult to pass (Bristol Stool Types 1-2).
• Straining: Significant effort is required to pass a bowel movement.
• Sensation of incomplete evacuation: A feeling that the rectum is not empty even after a bowel movement.
• Abdominal bloating and discomfort.
• Manual maneuvers: The need to use fingers to help pass stool or support the perineum.

What causes functional constipation?

The causes of functional constipation are not fully understood and are likely multifactorial. It is a 'functional' disorder, meaning there is a problem with how the gut and nervous system work together, rather than a structural problem.

• Slow-Transit Constipation: This is thought to be caused by a problem with the nerves that control the colon's muscle contractions (myenteric plexus), leading to reduced propulsive activity.
• Functional Outlet Obstruction: This is often a learned behavioral problem where a person loses the ability to coordinate the abdominal, rectal, and pelvic floor muscles to defecate. It can be initiated by painful bowel movements (like from an anal fissure) or other pelvic floor trauma.
• Dietary and Lifestyle Factors: While not the primary cause, low fiber intake, inadequate fluid consumption, and a sedentary lifestyle can contribute to and worsen constipation.
• Medications: Many medications can cause constipation as a side effect, including opioids, some antidepressants, and calcium channel blockers.

How is functional constipation diagnosed?

Diagnosis begins with a thorough history and physical exam to rule out secondary causes and to identify the predominant symptoms. If first-line treatments like fiber and over-the-counter laxatives fail, specialized testing may be recommended to determine the underlying subtype.

• Colonoscopy: To rule out any mechanical obstruction or other structural abnormalities within the colon.
• Colonic Transit Study (Sitz Marker Study): The patient swallows a capsule containing small radiopaque markers. An abdominal X-ray is taken several days later (usually day 5) to see how many markers remain in the colon. Retention of more than 20% of the markers suggests slow-transit constipation.
• Anorectal Manometry: A small catheter is placed in the rectum to measure the pressures of the anal sphincter muscles and to assess rectal sensation and reflexes. It is the key test to diagnose dyssynergic defecation.
• Balloon Expulsion Test: A small, water-filled balloon is placed in the rectum, and the patient is asked to expel it. An inability to expel the balloon within a certain time frame (usually 1-2 minutes) suggests a defecatory disorder.
• Defecography: A dynamic imaging study (X-ray or MRI) that visualizes the defecation process. It can identify structural problems like a large rectocele and functional problems like dyssynergic defecation or internal rectal prolapse.

How is functional constipation treated?

Treatment is tailored to the underlying subtype and the severity of symptoms.

General Measures and Medical Therapy:

• Fiber and Fluids: The first step for all types is to ensure adequate intake of dietary fiber (20-30 grams/day) and fluids.
• Laxatives: If fiber is not sufficient, over-the-counter osmotic laxatives like polyethylene glycol (PEG) are safe and effective for long-term use. Stimulant laxatives (e.g., senna, bisacodyl) can be used for more severe symptoms.
• Prescription Medications: For more refractory constipation, several prescription medications are available:
  • Secretagogues (e.g., lubiprostone, linaclotide, plecanatide): These drugs work by increasing fluid secretion into the colon.
  • Serotonin Agonists (e.g., prucalopride): These drugs stimulate colonic motility.

Specific Treatments for Subtypes:

• Dyssynergic Defecation (Outlet Obstruction): The most effective treatment is pelvic floor biofeedback. This is a specialized form of physical therapy where a therapist uses sensors to give the patient real-time feedback on their muscle activity, teaching them how to properly relax the pelvic floor and coordinate their muscles to defecate effectively.
• Slow-Transit Constipation: For patients who fail aggressive medical management, surgery may be an option. A total abdominal colectomy with ileorectal anastomosis can be very effective in highly selected patients who have confirmed slow transit and no evidence of a significant outlet obstruction.

Self-Care for Constipation

• Establish a Routine: Try to have a bowel movement at the same time each day, often after a meal, to take advantage of the natural colonic contractions.
• Proper Toileting Posture: Using a small footstool to elevate your feet while on the toilet can help to straighten the anorectal angle and make evacuation easier.
• Do Not Ignore the Urge: Go to the bathroom as soon as you feel the urge to have a bowel movement.
• Regular Exercise: Physical activity can help to stimulate bowel function.

Is it harmful to use laxatives long-term?
For many years, there was concern that long-term use of stimulant laxatives could damage the nerves of the colon. However, there is no good evidence to support this belief. Osmotic laxatives like polyethylene glycol are considered very safe for long-term daily use. It is always best to discuss your laxative regimen with your doctor.

What is the difference between functional constipation and IBS-C?
The main difference is the presence of abdominal pain. According to the Rome IV criteria, to be diagnosed with Irritable Bowel Syndrome with Constipation (IBS-C), abdominal pain must be a prominent symptom, occurring at least one day per week on average and related to defecation. In functional constipation, abdominal pain is not a primary complaint.

When is surgery a good option for constipation?
Surgery is a last resort for constipation and is only considered for the most severe cases of slow-transit constipation that have failed all other medical treatments. It is not an effective treatment for outlet obstruction or IBS-C. Patient selection is critical, and a full workup including transit studies and tests to rule out outlet obstruction is mandatory before considering surgery.

• Garrett KA, Ogilvie Jr JW. Evaluation of Constipation and Treatment of Abdominal Component. In: Steele SR, Hull TL, Hyman N, Maykel JA, Read TE, Whitlow CB, eds. The ASCRS Textbook of Colon and Rectal Surgery. 4th ed. Springer; 2022:995-1004.
• Zutshi M, Oliveira LCC. Treatment of Difficult/Obstructive Defecation. In: Steele SR, Hull TL, Hyman N, Maykel JA, Read TE, Whitlow CB, eds. The ASCRS Textbook of Colon and Rectal Surgery. 4th ed. Springer; 2022:1007-1017.
• National Institute of Diabetes and Digestive and Kidney Diseases. Constipation. Published May 2018. Accessed October 12, 2025. https://www.niddk.nih.gov/health-information/digestive-diseases/constipation
• Mayo Clinic. Constipation. Accessed October 12, 2025. https://www.mayoclinic.org/diseases-conditions/constipation/symptoms-causes/syc-20354253