Constipation in Adults
Clinical Snapshot
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.
Recognize the Condition
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]
The 3 pathophysiological types of chronic constipation
Slow-transit constipation
Delayed movement of stool through the colon from impaired colonic motility. Infrequent urge to defecate is typical, and response to fibre alone is often poor.
Defecatory disorders (pelvic floor dysfunction / dyssynergia)
Impaired coordination of the rectoanal and pelvic floor muscles during attempted defecation, producing straining and a sensation of incomplete evacuation despite normal colonic transit. Responds poorly to fibre and laxatives alone — needs anorectal testing and biofeedback therapy, not laxative escalation.
Normal-transit (functional) constipation
The most common type. Colonic transit and pelvic floor function are both normal, but the patient perceives infrequent, hard, or difficult-to-pass stool. Generally responds well to fibre, fluid, and standard laxative therapy.
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.
Risk Factors
- 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.
Red Flags & Refer
Rule out these features before labeling constipation as functional/idiopathic. Any of the following warrants further investigation (colonoscopy, sigmoidoscopy, or urgent referral as clinically indicated) rather than a trial of laxative therapy alone:
- Rectal bleeding or evidence of GI bleeding.
- Unintentional weight loss.
- Unexplained iron-deficiency anemia.
- Family history of colorectal cancer.
- New onset of symptoms at or after 50 years of age (screening colonoscopy is separately recommended starting at this age regardless of symptoms).
- Palpable abdominal mass.
- Sudden or acute onset of a change in bowel habits.
- Severe symptoms that do not respond to pharmacologic management and adversely affect normal daily activities.
- Acute severe abdominal pain, distension, vomiting, or other signs suggesting bowel obstruction — this needs emergency assessment, not outpatient laxative titration.
Assessment & Diagnosis
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
| 2 or more of the following, present for the last 3 months, with symptom onset at least 6 months before diagnosis | |
|---|---|
| Lumpy or hard stools in more than 1 in 4 defecations | |
| Straining in more than 1 in 4 defecations | |
| Fewer than 3 spontaneous bowel movements per week | |
| A sensation of incomplete evacuation in more than 1 in 4 defecations | |
| A sensation of anorectal obstruction or blockage in more than 1 in 4 defecations | |
| Manual manoeuvres needed to facilitate more than 1 in 4 defecations (e.g., digital evacuation, support of the pelvic floor) | |
| Loose stools are rarely present without the use of laxatives | |
| Criteria for irritable bowel syndrome are not met |
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]
Treatment Targets
- 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.
Choose Initial Treatment
Two different pathways: functional/chronic idiopathic constipation vs. opioid-induced constipation
Functional / chronic idiopathic constipation
A stepwise escalation from lifestyle measures through osmotic laxatives, then stimulant laxatives, reserving secretagogues and prokinetics for patients who fail laxatives from at least 2 classes.
Opioid-induced constipation (OIC)
Managed proactively from the moment an opioid is started, using a stimulant or osmotic laxative — not a bulk-forming agent alone — with escalation to a peripherally acting mu-opioid receptor antagonist (PAMORA) if laxatives remain inadequate.
Functional / chronic idiopathic constipation
Confirm the diagnosis first — exclude red-flag features and, when the history suggests it, perform a digital rectal examination before committing to a functional diagnosis.
1st line, all patients a supervised trial of dietary fibre, adequate fluid intake, and behavioural measures (see Non-Pharmacologic Treatment) before starting drug therapy, continued alongside any drug therapy that follows.[5]
1st-line pharmacotherapy — use when nonpharmacologic measures alone are inadequate an osmotic laxative, preferring polyethylene glycol (PEG) over lactulose: PEG produces greater improvements in stool frequency and form, relieves abdominal pain, and reduces the need for additional laxatives.[5]
2nd line — use when an osmotic laxative alone is inadequate add or switch to a stimulant laxative (bisacodyl or sennosides). Stimulant laxatives are effective for both acute and chronic constipation and are appropriate for regular use in patients who need it, including long-term use in patients on chronic opioid therapy.[5]
Refractory — use when laxatives from at least 2 different classes (osmotic and stimulant), at an adequate dose and duration, have failed a secretagogue (linaclotide or plecanatide) or a prokinetic (prucalopride). Prucalopride initiation is best done by, or in consultation with, a clinician experienced in treating chronic constipation.[5]
Bulk-forming fibre supplements (e.g., psyllium) are a reasonable adjunct for normal-transit/mild functional constipation and are safe for long-term use, but patients with a defecatory disorder or slow-transit constipation often respond poorly to fibre alone — persistent symptoms despite an adequate fibre trial should prompt escalation rather than further fibre increases.
Do not rely on docusate as primary constipation therapy for any type of constipation, including opioid-induced constipation — current evidence does not support its efficacy.
Opioid-induced constipation
1st line, started proactively at the time an opioid is prescribed a stimulant laxative (bisacodyl or sennosides) or an osmotic laxative (PEG or lactulose) in any patient starting an opioid, or with a history of OIC — do not wait for constipation to develop before treating it.[6]
Do not rely on a bulk-forming agent alone for OIC — bulk-forming agents will not overcome the reduction in colonic peristalsis caused by opioid receptor agonism and may worsen bloating without benefit.
2nd line — use when scheduled laxative therapy remains inadequate add a peripherally acting mu-opioid receptor antagonist (PAMORA): naloxegol for non-palliative populations, or methylnaltrexone specifically in patients receiving palliative care.[6]
Where clinically appropriate, consider opioid dose de-escalation or switching to an equianalgesic dose of a less-constipating opioid — transdermal fentanyl is less constipating than sustained-release oral morphine at an equivalent analgesic dose.
Non-Pharmacologic Treatment
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.
Special Populations
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.
Monitoring & Follow-Up
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.
Common Errors to Avoid
- 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.
Clinical Decision Algorithm
Drug Tables
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.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Psyllium | Adults: 3.4 g PO once daily to TID | Bloating, flatulence, abdominal discomfort; rare esophageal/colonic obstruction, rare allergic reaction | May reduce or delay absorption of other oral drugs (e.g., digoxin, lithium, carbamazepine, warfarin) — separate dosing by at least 2 hours | Onset 12-72 h. Take with at least 250 mL fluid. Do not take within 2 h of other medications. Suitable for long-term use. |
Osmotic and saline laxatives
PEG is preferred over lactulose and the magnesium/phosphate salts for routine chronic use, given fewer electrolyte concerns.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Polyethylene glycol (PEG) 3350 | Adults: 17 g PO once daily, may increase to BID if needed | Nausea, cramping, diarrhea; rare hives/skin rash | None significant — not absorbed | Onset 2-4 days. Dissolve in 250 mL water, juice, soda, coffee, or tea. Contains no electrolytes — a reasonable choice in renal or cardiac dysfunction. |
| Lactulose | Adults: 15-30 mL PO once daily to BID | Bloating, flatulence, cramps, diarrhea | None significant | Onset 24-48 h. Also used at different dosing for hepatic encephalopathy — confirm the intended indication before adjusting the dose. |
| Magnesium citrate | Adults: 3.75-7.5 g (75-150 mL) PO once daily, with 250 mL water | Cramping, bloating, diarrhea, nausea; hypermagnesemia in renal dysfunction | Decreases absorption of quinolone and tetracycline antibiotics — separate by at least 2 h | Onset 30 min-6 h. Useful when a rapid response is required (e.g., before colonoscopy or surgery). Avoid in renal failure. |
| Magnesium hydroxide | Adults: 2.4-4.8 g (30-60 mL) PO once daily or in divided doses | Diarrhea, cramping; hypermagnesemia in renal dysfunction | Decreases absorption of quinolone and tetracycline antibiotics — separate by at least 2 h | Onset 30 min-6 h. Also used as an antacid at lower, more frequent doses. Avoid in renal failure. |
| Magnesium sulfate (oral) | Adults: 10-30 g dissolved in 240 mL water or juice, PO once daily or divided | Cramping, diarrhea, nausea; hypermagnesemia in renal dysfunction | Decreases absorption of quinolone and tetracycline antibiotics — separate by at least 2 h | Onset 30 min-6 h. Oral laxative use only — distinct from the topical soak and from intravenous magnesium sulfate. Avoid in renal failure. |
| Sodium phosphates, oral | Adults: 20 mL diluted in 120 mL cool water/clear liquid PO as a single dose, followed by 240 mL water/clear liquid | Hyperphosphatemia and hypocalcemia (especially in renal dysfunction); acute phosphate nephropathy; arrhythmia with excess dosing | Additive kidney-injury risk with ACE inhibitors, ARBs, diuretics, NSAIDs | Onset 30 min-6 h. No longer recommended as a bowel-cleansing/prep agent given phosphate-nephropathy risk — reserve for occasional use only, in patients without renal risk factors. Avoid in renal failure. |
| Sodium phosphates, enema | Adults: 118 mL (1 bottle) PR as a single dose | Rectal discomfort, cramping; hyperphosphatemia and hypocalcemia if retained or used repeatedly | Additive kidney-injury risk with ACE inhibitors, ARBs, diuretics, NSAIDs | Onset 2-15 min. Do not use more than once in 24 hours. Use the pediatric-strength product, not the adult product, in children. Avoid in renal failure. |
| Glycerin suppository | Adults: 1 suppository (2.6 g) PR once daily to BID or PRN | Rectal discomfort or burning | None significant — minimal systemic absorption | Onset 15 min-1 h. Insert high into the rectum and retain 15 minutes if possible. Use the pediatric strength, not the adult strength, in children. |
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.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Bisacodyl | Oral: 5-10 mg PO once daily or PRN Rectal: 10 mg suppository once daily or PRN | Abdominal cramping; rectal microscopic mucosal changes with suppository/enema use | None significant | Onset 6-12 h (oral), 15-60 min (rectal). Usually short-term, but long-term use may be necessary in patients on chronic opioid therapy. |
| Sennosides | Adults: 8.6-32.4 mg (1-4 tablets) PO once daily or at bedtime | Abdominal cramping, diarrhea; melanosis coli (benign, reversible) with chronic use | Chronic/excessive use may increase potassium loss, potentiating digoxin toxicity and adding to diuretic/corticosteroid-induced hypokalemia | Onset 6-12 h. Bedtime dosing is common. Long-term use may be necessary 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.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Docusate sodium | Adults: 100-200 mg PO daily | Mild cramping; generally well tolerated | May increase systemic absorption (and toxicity risk) of mineral oil or danthron-type stimulant laxatives if combined | Do not substitute for an osmotic or stimulant laxative. Limit to short-term use if used at all. |
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.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Linaclotide | Adults, standard dose: 145 mcg PO once daily Adults, if diarrhea/intolerance at standard dose: 72 mcg PO once daily | Diarrhea, upper abdominal pain | None significant — minimal systemic absorption | Onset about 1 week. Take at least 30 min before the first meal. Contraindicated under 6 years of age; avoid ages 6-17. |
| Plecanatide | Adults: 3 mg PO once daily | Diarrhea | None significant — minimal systemic absorption | May be taken with or without food; may be crushed for patients with swallowing difficulty per product labelling. Contraindicated under 6 years of age; avoid ages 6-17. |
Serotonin 5-HT4 receptor agonist (prokinetic)
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Prucalopride | Women 65 y or younger: 2 mg PO once daily Women over 65 y: 1 mg PO once daily, may increase to 2 mg if needed | Abdominal pain, diarrhea, headache, nausea | None significant | Onset within 4 weeks; discontinue if ineffective after 4 weeks. Health Canada's approved indication is for adult women; best initiated by a clinician experienced in treating chronic constipation. |
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.
| Drug | Dosage | Adverse effects | Drug interactions | Comments |
|---|---|---|---|---|
| Naloxegol | Adults, standard renal function: 25 mg PO once daily Adults, moderate/severe/end-stage renal impairment: 12.5 mg PO once daily, may increase to 25 mg if tolerated | Abdominal pain, back pain, diarrhea, flatulence, headache, hyperhidrosis, nausea, vomiting | Contraindicated with strong CYP3A4 inhibitors (clarithromycin, ketoconazole, ritonavir, voriconazole); not recommended with other CYP3A4 inhibitors/inducers | Onset about 12 h. Take on an empty stomach. Stop maintenance laxatives before starting; may resume if response inadequate after 3 days. |
| Methylnaltrexone | 33-37 kg: 6 mg SC every 2 days 38-61 kg: 8 mg SC every 2 days 62-114 kg: 12 mg SC every 2 days 115-126 kg: 18 mg SC every 2 days Other weights: 0.15 mg/kg SC every 2 days | Abdominal pain, flatulence, nausea, increased body temperature, dizziness; rare bowel perforation | None significant | Onset about 4 h. For OIC in patients receiving palliative care with inadequate response to laxatives. Consider discontinuing after 4 doses (about 1 week) without response. Use with extreme caution in patients at increased perforation risk (tumor infiltration, acute intestinal inflammation, concurrent corticosteroid/NSAID/biologic therapy). |
References
- The pathophysiology of chronic constipation — Canadian Journal of Gastroenterology (Andrews CN, Storr M). Can J Gastroenterol 2011;25(Suppl B):16B-21B
- Bowel Disorders — Gastroenterology (Lacy BE, Mearin F, Chang L, et al.). Gastroenterology 2016;150(6):1393-1407
- Stool form scale as a useful guide to intestinal transit time — Scandinavian Journal of Gastroenterology (Lewis SJ, Heaton KW). Scand J Gastroenterol 1997;32(9):920-924
- AGA Clinical Practice Update on Evaluation and Management of Refractory Constipation: Expert Review — Clinical Gastroenterology and Hepatology (Staller K, et al.). Clin Gastroenterol Hepatol 2026
- American Gastroenterological Association-American College of Gastroenterology Clinical Practice Guideline: Pharmacological Management of Chronic Idiopathic Constipation — American Journal of Gastroenterology (Chang L, Chey WD, Imdad A, et al.). Am J Gastroenterol 2023;118(6):936-954
- American Gastroenterological Association Institute Guideline on the Medical Management of Opioid-Induced Constipation — Gastroenterology (Crockett SD, Greer KB, Heidelbaugh JJ, et al.). Gastroenterology 2019;156(1):218-226
- Nutrients in food: Fibre — Health Canada. Health Canada, Nutrients in Food
Professional reference only. Apply clinical judgment and verify patient-specific decisions against current authoritative guidance and product information.