Functional constipation is constipation that does not have a physical (anatomical) or physiological (hormonal or other body chemistry) cause. It may have a neurological, psychological or psychosomatic cause. A person with functional constipation may be healthy, yet has difficulty defecating.

Functional constipation, as medically defined by the Rome III criteria, has many causes, including:

• Anismus
• Descending perineum syndrome
• Hirschsprung's disease
• Other inability or unwillingness to control the external anal sphincter, which normally is under voluntary control
• A bad diet
• an unwillingness to defecate
• nervous reactions, including prolonged and/or chronic stress and anxiety, that close the inner anal sphincter, a muscle that is not under voluntary control
• deeper psychosomatic disorders which sometimes affect digestion and the absorption of water in the colon

See also

• Functional symptom