Constipation or irregularity, is a condition of the digestive system where a person (or animal) experiences hard feces that are difficult to egest. It may be extremely painful, and in severe cases (fecal impaction) lead to symptoms of bowel obstruction. The term obstipation is used for severe constipation. Causes of constipation may be dietary, hormonal, anatomical, a side effect of medications (e.g. some painkillers), or an illness or disorder. Treatments consist of changes in dietary and exercise habits, the use of laxatives, and other medical interventions depending on the underlying cause.

The main causes of constipation include:

Hardening of the feces
Improper mastication (chewing) of food
Insufficient intake of dietary fiber
Dehydration from any cause or inadequate fluid intake
Medication, e.g. diuretics and those containing iron, calcium, aluminium
Paralysis or slowed transit, where peristaltic action is diminished or absent, so that feces are not moved along
Hypothyroidism (slow-acting thyroid gland)
Hypokalemia
Injured anal sphincter (patulous anus)
Medications, such as loperamide, opioids (e.g. codeine & morphine) and certain tricyclic antidepressants
Severe illness due to other causes
Acute porphyria (a rare inherited condition)
Lead poisoning
Dyschezia (usually the result of suppressing defecation)
Constriction, where part of the intestine or rectum is narrowed or blocked, not allowing feces to pass
Stenosis (Strictures)
Diverticula
Tumors, either of the bowel or surrounding tissues
Retained foreign body or a bezoar
Psychosomatic constipation, based on anxiety or unfamiliarity with surroundings.
Functional constipation
Constipation-predominant irritable bowel syndrome, characterized by a combination of constipation and abdominal discomfort and/or pain[4]
Smoking cessation (tobacco smoking has a laxative effect)[5]
Abdominal surgery, other types of surgery, childbirth