Constipation in Adults

Constipation is broadly defined as unsatisfactory defecation, characterized by infrequent stools, difficult stool passage, or both.^[1] On the basis of pathophysiology, there are 3 primary types — slow-transit constipation, defecatory disorders (pelvic floor dysfunction/dyssynergia), and normal-transit (functional) constipation — and functional constipation can be precisely defined using the Rome IV criteria.^[2] Constipation-predominant irritable bowel syndrome (IBS-C) is closely related but is a distinct diagnosis, distinguished by abdominal pain that is specifically related to bowel movements. Constipation is a symptom, not a disease — identifying a potential underlying or reversible cause (including the very common scenario of a constipating medication) and correcting it is the primary objective of assessment, not simply reaching for a laxative.

Typical presentation

Patients describe some combination of: infrequent bowel movements (fewer than 3 per week), hard or lumpy stools, excessive straining, a sensation of incomplete evacuation, a sensation of anorectal blockage, the need for manual manoeuvres to complete defecation (digital evacuation, splinting/support of the perineum), bloating, and abdominal discomfort. A patient's own definition of "normal" varies widely — some believe a daily bowel movement is required for health when it is not — so history should establish each patient's baseline rather than assuming a fixed frequency threshold. Stool form can be objectively characterized using the 7-point Bristol Stool Form Scale, where types 1-2 indicate constipation, types 3-4 are ideal consistencies, and types 5-7 suggest diarrhea or urgency.^[3]

Constipation-predominant IBS is a related but distinct diagnosis

IBS-C shares the stool-frequency and stool-form features of functional constipation but requires abdominal pain that is specifically associated with defecation — pain is not a Rome IV feature of functional constipation itself. A patient whose dominant complaint is pain tied to bowel movements, rather than the mechanical symptoms above, needs the distinct IBS management approach rather than straightforward constipation therapy.

• Older age and physical inactivity or immobilization.
• Low dietary fibre and fluid intake.
• Female sex; pregnancy.
• Neurologic disease — Parkinson disease, multiple sclerosis, spinal cord injury/dysfunction, stroke.
• Endocrine/metabolic disease — hypothyroidism, diabetes mellitus, hypercalcemia.
• Connective tissue disease — progressive systemic sclerosis (scleroderma).
• Structural abnormalities or prior pelvic/anorectal surgery.
• Painful anorectal conditions (fissure, thrombosed hemorrhoid) that lead to voluntary stool retention.
• Psychological factors — depression, a history of abuse, eating disorders.

Medications are a common and correctable cause — always review the drug list

A thorough medication review is one of the highest-yield steps a pharmacist can take, since many constipating drugs have a viable alternative. Constipating drug classes include:

• Opioids, e.g., codeine, morphine — the single most important class to identify, since it warrants its own proactive management pathway rather than reactive laxative use (see Choose Initial Treatment).
• Antacids containing aluminum or calcium.
• Bismuth preparations.
• Anticonvulsant agents.
• Diuretics that cause hypokalemia.
• Resins, e.g., cholestyramine.
• Antiparkinsonian agents.
• Drugs with anticholinergic properties, e.g., amitriptyline and other tricyclic antidepressants, first-generation antihistamines.
• Serotonin receptor antagonists, e.g., ondansetron.
• Antipsychotic agents.
• Drugs with neurotoxicity, e.g., checkpoint inhibitors, vincristine.
• Sucralfate.
• Antispasmodics.
• Iron-containing products.
• Verapamil and other non-dihydropyridine calcium channel blockers.

Discontinuing or switching a constipating medication, when clinically feasible, should always be attempted before or alongside starting laxative therapy — treating the symptom while leaving an easily correctable cause in place is a common, avoidable error.

History

• The patient's own definition and baseline of "normal" bowel habit, and the duration of the current change.
• The most distressing feature specifically — infrequency, straining, hard stool, unusual toilet postures, need for digital manipulation, sensation of incomplete evacuation, bloating, or pain.
• Previous laxative use and response.
• Dietary fibre and fluid intake, physical activity level.
• A complete medication review for constipating drugs (see Risk Factors).
• Structural abnormalities or previous relevant surgery.
• Symptoms suggesting an alternative or secondary cause — obstructive symptoms (concern for colonic neoplasm or stricture, anal stricture), painful hemorrhoid or fissure, pregnancy, neuromuscular disease, endocrine disorder, connective tissue disorder.

Physical examination

Perform an abdominal, perineal, and rectal examination, looking for abdominal or rectal masses, anorectal fissures, and hemorrhoids. A digital rectal examination — including assessment of pelvic floor motion during simulated evacuation — should be performed before a patient is labeled as having functional constipation. A normal digital rectal exam does not exclude a defecatory disorder, so a suggestive history still warrants further anorectal testing even when the exam is unremarkable.^[4]

Rome IV diagnostic criteria for functional constipation

Rome IV criteria for functional constipation.^[2]

Laboratory testing

Reserve laboratory testing for patients whose history suggests systemic disease — routine bloodwork is not indicated for uncomplicated functional constipation. When indicated: CBC, serum electrolytes (including calcium), creatinine, and TSH.

When lower endoscopy is — and is not — indicated

Routine use of colonoscopy or sigmoidoscopy is not recommended for uncomplicated constipation. Consider sigmoidoscopy, colonoscopy, or (less commonly) CT colonography when any of the following are present: new onset of symptoms at or after 50 years of age, severe symptoms that do not respond to pharmacologic management, any red-flag/alarm feature (see Red Flags & Refer), or a family history of colorectal cancer.

Testing reserved for refractory or specialist-directed workup

Before a patient is formally labeled as having refractory constipation, confirm an adequate trial of nonpharmacologic measures plus laxatives from at least 2 different classes, exclude a correctable secondary cause (including medications), and confirm the presence of slow colonic transit or a defecatory disorder using dedicated testing.^[4] These tests are typically ordered by, or in consultation with, a gastroenterologist rather than as first-line primary-care investigations:

• Anorectal manometry with balloon expulsion testing — the recommended first anorectal test to identify a defecatory disorder before further imaging.
• Colonic transit study — radiopaque marker study or a wireless motility capsule, to confirm slow-transit constipation.
• Defecography — barium or dynamic MR defecography, considered when clinical features suggest a structural abnormality or when anorectal manometry and balloon expulsion testing are inconclusive.

A course of pelvic floor biofeedback therapy, when a defecatory disorder is confirmed, should generally be completed before a patient is considered to have failed all available treatment.^[4]

• Establish regular, patient-appropriate bowel function.
• Eliminate the need to strain, preventing straining-related complications — hernia, gastroesophageal reflux, hemorrhoidal prolapse, aggravation of bladder or uterine prolapse, and cardiac or cerebrovascular strain in older adults.
• Prevent constipation-related complications — hemorrhoids, anal fissure, rectal prolapse, stercoral ulcer, fecal impaction, fecal incontinence.
• Treat any complication that has already occurred, e.g., fecal impaction, intestinal obstruction.
• Identify and correct or remove a reversible underlying cause — including a constipating medication — rather than treating the symptom in isolation.
• For opioid-induced constipation specifically: prevent it proactively from the time an opioid is started, rather than treating it only once established.

Dietary measures

• Encourage adequate dietary fibre intake — a target of approximately 25 g/day for women and 38 g/day for men^[7] — from legumes, whole grains, vegetables, fruits, flaxseed, psyllium, and unprocessed bran.
• Increase fibre intake gradually to minimize flatulence, bloating, and cramping.
• Recommend increased fluid intake (approximately 2.2 to 3 L/day) to complement a high-fibre diet.

Behavioural measures

• Encourage a regularly scheduled toilet time to develop a conditioned gastrocolic reflex, e.g., after breakfast.
• Advise against ignoring the urge to defecate.
• Advise against prolonged straining.
• Advise raising the legs while defecating (squatting, or using a footstool), which straightens the anorectal angle and may facilitate defecation.
• Encourage regular physical exercise.

Medication review

Discontinue or switch a constipating medication whenever clinically feasible (see Risk Factors for the full list of constipating drug classes) — this is often the single highest-yield intervention available and should be revisited at every follow-up, not just at diagnosis.

Dyssynergic defecation

For constipation due to dyssynergic defecation (pelvic floor dysfunction), pelvic floor physiotherapy — relaxation exercises for the pelvic floor and external anal sphincter — combined with biofeedback therapy (neuromuscular retraining to restore normal defecation) is the appropriate treatment, not further laxative escalation.

Digital stimulation and suppositories in spinal cord dysfunction

Digital stimulation of the anal sphincter, including insertion of a glycerin suppository, can help trigger evacuation as part of a scheduled bowel program in patients with spinal cord injury or dysfunction.

Pregnancy

A greater proportion of pregnant patients experience constipation during the first 2 trimesters than the third; in later pregnancy it is attributed to rising progesterone reducing GI motility, and iron supplementation can also contribute. Encourage nonpharmacologic measures first. 1st line in pregnancy bulk-forming agents (psyllium) — not systemically absorbed. If constipation persists, a magnesium-containing liquid antacid can help and also relieves heartburn, which is common in the third trimester. Senna or bisacodyl may be used short-term. Reserve PEG or lactulose for constipation refractory to fibre and a short stimulant-laxative trial. Do not use docusate (not effective), linaclotide or plecanatide (insufficient pregnancy data), prucalopride (not recommended in pregnancy), castor oil (can induce premature uterine contractions), or mineral oil (can impair fat-soluble vitamin absorption with chronic use and cause lipoid pneumonia if aspirated). Avoid routine use of magnesium- or phosphate-containing saline laxatives at bowel-prep-type doses in pregnancy given the electrolyte load and limited safety data — prefer PEG or lactulose if an osmotic agent beyond fibre is required.

Breastfeeding

Bulk-forming agents are preferred — not systemically absorbed, lower cost, favourable side-effect profile. Magnesium hydroxide is considered 2nd line. Senna and bisacodyl are acceptable but recommended only for short-term use. Do not use docusate (not effective), linaclotide or plecanatide (insufficient breastfeeding data), prucalopride (not recommended while breastfeeding), or other laxatives lacking breastfeeding safety data.

Older adults

PEG is safe and effective in geriatric patients and is often preferred given its favourable tolerability and lack of electrolyte content. Use magnesium- or phosphate-containing saline laxatives with particular caution, since age-related decline in renal function increases the risk of accumulation. Some older patients benefit from a combination of laxatives with different mechanisms (e.g., a bulk-forming agent plus a stimulant laxative) when monotherapy is inadequate. Reinforce that straining itself carries real risk in this population — cardiac and cerebrovascular strain, hemorrhoidal or pelvic organ prolapse — reinforcing the importance of adequate treatment rather than under-treating constipation as a minor complaint.

Renal impairment

Avoid magnesium-containing (magnesium citrate, magnesium hydroxide, magnesium sulfate) and phosphate-containing (oral or enema sodium phosphates) laxatives — accumulation risk in reduced renal clearance. PEG is preferred in this population since it is not absorbed and contains no electrolytes. Naloxegol requires a reduced starting dose (12.5 mg once daily) in moderate, severe, or end-stage renal impairment.

Palliative care / advanced illness

A scheduled combination of a stimulant and an osmotic laxative is standard for a bowel regimen in patients on chronic opioid therapy. Methylnaltrexone is specifically indicated for OIC in patients receiving palliative care who have had an inadequate response to laxatives.

Pediatrics

Constipation in children is assessed and managed differently, with its own red flags, dosing, and diagnostic thresholds, and is addressed as a separate condition — this chapter is for adults only. Note, however, that several adult drugs discussed here carry specific pediatric contraindications relevant to a caregiver's medicine cabinet: linaclotide and plecanatide are both contraindicated under 6 years of age because of a risk of serious dehydration seen in juvenile animal studies, and should be avoided from ages 6 to 17 as well, since safety and effectiveness have not been established in that age group.

Reassess response after an adequate trial of the current step before escalating: allow several days for an osmotic or stimulant laxative, and a full 4 weeks before declaring a secretagogue, plecanatide, or prucalopride ineffective. For methylnaltrexone, reconsider continued use if there has been no response after 4 doses (about 1 week). Track bowel frequency, stool form (Bristol scale), and the patient's most bothersome symptom at each visit rather than relying on a single global "better or worse" impression. Monitor electrolytes in patients on chronic or higher-dose osmotic-saline laxative therapy, particularly those with renal impairment. Revisit the medication list at every follow-up for any newly added constipating drug. In patients on opioids, proactively reassess the bowel regimen at every opioid dose change or opioid switch, rather than waiting for the patient to report new symptoms. Long-term laxative use is not an absolute indication to stop — when a patient wants to try stopping, taper gradually over 3-4 weeks while reinforcing nonpharmacologic measures, and use an osmotic laxative intermittently as needed until bowel regularity is re-established.

1. Confirm adherence to nonpharmacologic measures and to the current pharmacotherapy at the correct dose, formulation, and duration before assuming the drug itself has failed.
2. Repeat the medication review for any newly started or missed constipating drug.
3. Escalate by adding or switching to a different mechanism rather than repeatedly increasing the dose of the same laxative class — osmotic to stimulant, or stimulant/osmotic combination to a secretagogue or prokinetic.
4. Reconsider red-flag features and the need for colonic investigation if not already performed, especially with new or worsening symptoms.
5. Before labeling constipation as refractory, confirm an adequate trial of laxatives from at least 2 classes plus nonpharmacologic measures, then refer for anorectal manometry with balloon expulsion testing (± colonic transit study or defecography) rather than continuing to escalate laxative doses indefinitely.
6. If a defecatory disorder is confirmed, complete a course of pelvic floor biofeedback therapy before considering further pharmacologic escalation.
7. For opioid-induced constipation refractory to a scheduled stimulant/osmotic regimen, escalate to a PAMORA (naloxegol or methylnaltrexone as appropriate to the care setting) rather than adding further conventional laxatives alone.
8. If constipation remains refractory after a complete workup and adequate trials across all these steps, refer to gastroenterology for consideration of a colonic transit study (if not already done) and possible surgical evaluation in select cases of confirmed slow-transit constipation.

• Labeling constipation "functional" without a digital rectal examination or without excluding red-flag features first.
• Relying on docusate as primary therapy — current evidence does not support its efficacy for any constipation type.
• Recommending a bulk-forming fibre supplement as the primary therapy for opioid-induced constipation — it does not address the underlying mechanism and will not adequately relieve OIC.
• Using an oral sodium phosphate product as a routine bowel-cleansing agent before colonoscopy — this is no longer recommended given the risk of acute phosphate nephropathy; other bowel-prep agents are preferred.
• Not starting a prophylactic laxative at the time an opioid is initiated, and instead waiting for constipation to develop.
• Escalating the dose of the same laxative class indefinitely instead of adding or switching to a different mechanism.
• Missing a reversible medication-induced cause during a routine medication review.
• Assuming a daily bowel movement is required for "normal" bowel function — the patient's own baseline matters more than a fixed frequency.
• Starting prucalopride or a secretagogue before an adequate trial of laxatives from at least 2 conventional classes.
• Recommending a magnesium- or phosphate-containing laxative without first checking renal function.
• Using an adult-strength rectal product (glycerin suppository, sodium phosphate enema) in a child, or vice versa — pediatric-strength formulations exist specifically to avoid this.

How to use this table: doses are adult doses and require patient-specific confirmation, including renal adjustment. Select any drug name to open its complete Pharmasist Drug Database page.

Bulk-forming agents

Effective and safe for long-term use, but must be taken with adequate fluid; poor response is common in defecatory disorders and slow-transit constipation.

Osmotic and saline laxatives

PEG is preferred over lactulose and the magnesium/phosphate salts for routine chronic use, given fewer electrolyte concerns.

Stimulant laxatives

Effective for acute and chronic constipation; commonly associated with cramping, but long-term use is appropriate when needed, e.g., in patients on chronic opioid therapy.

Stool softener — evidence does not support efficacy

Included for completeness since it remains widely used; current evidence does not support recommending it as primary therapy for any constipation type, including opioid-induced constipation.

Guanylate cyclase-C agonists (secretagogues)

Reserve for chronic idiopathic constipation or IBS-C refractory to laxatives from at least 2 classes; minimal systemic absorption for both agents.

Serotonin 5-HT4 receptor agonist (prokinetic)

Peripherally acting mu-opioid receptor antagonists (PAMORAs)

For opioid-induced constipation refractory to a scheduled stimulant/osmotic laxative regimen — not for constipation unrelated to opioid use.