Skip to content

Constipation-predominant pharmacotherapy (IBS-C)

TL;DR — IBS-C has the best-regulated drug class in the condition: four licensed secretagogues or secretagogue-like agents tested against the FDA composite responder endpoint in trials of 500–2,200 patients each. All beat placebo; none beats another. The network meta-analysis of 15 RCTs and 8,462 patients ranked linaclotide 290 µg once daily first on the FDA endpoint, each trial's own primary endpoint, abdominal pain and complete spontaneous bowel movements, with tenapanor 50 mg twice daily first for bloating — but "efficacy was similar among individual drugs and dosages for most end points" (Black 2018, PMID 30144426). Absolute responder rates are modest and placebo rates are high: linaclotide 33.7% vs 13.9% (NNT 5.1, 3.9–7.1) over 26 weeks (Chey 2012, PMID 22986437); tenapanor 36.5% vs 23.7% (p<0.001) over 26 weeks (Chey 2021, PMID 33337659); plecanatide 30.2%/29.5% vs 17.8% and 21.5%/24.0% vs 14.2% in two identical phase 3 trials (Brenner 2018, PMID 29545635); lubiprostone 17.9% vs 10.1% (p=0.001) on a global relief question (Drossman 2009, PMID 19006537). The AGA's 2022 guideline makes only one strong recommendation — linaclotide (high certainty) — with conditional recommendations for tenapanor, plecanatide, tegaserod and lubiprostone (moderate certainty), PEG laxatives, tricyclics and antispasmodics (low certainty), and a conditional recommendation against SSRIs (Chang 2022, PMID 35738724). Harms are dominated by diarrhoea; the number needed to harm for discontinuation is 16 for tenapanor, 35 for linaclotide, 53 for lubiprostone, 58 for tegaserod, 59 for plecanatide (Busam 2026, PMID 40471839). Osmotic laxatives improve bowel frequency but not abdominal pain versus placebo (Chapman 2013, PMID 23835436) — the clearest demonstration that in IBS-C the pain and the constipation are separable problems.

The regulated agents

Drug Mechanism Pivotal evidence Responder rate vs placebo NNH (discontinuation)
Linaclotide 290 µg od Minimally absorbed guanylate cyclase-C agonist 26-week phase 3, n=804 (Chey 2012, PMID 22986437) 33.7% vs 13.9% on FDA composite (NNT 5.1, 3.9–7.1); pain criterion 48.9% vs 34.5% (NNT 7.0); CSBM criterion 47.6% vs 22.6% (NNT 4.0) 35 (p<0.01)
Tenapanor 50 mg bd First-in-class minimally absorbed inhibitor of intestinal sodium/hydrogen exchanger 3 (NHE3) T3MPO-2, 26-week phase 3, NCT02686138, n=593 ITT (Chey 2021, PMID 33337659) 36.5% vs 23.7% (p<0.001) on 6/12-week combined responder 16 (p<0.01) — highest risk of the class
Plecanatide 3 or 6 mg od Guanylate cyclase-C agonist (uroguanylin analogue) Two identical 12-week phase 3 trials, n=2,189 randomised (Brenner 2018, PMID 29545635) Study 1: 30.2% (3 mg) / 29.5% (6 mg) vs 17.8%; Study 2: 21.5% / 24.0% vs 14.2% 59 (p<0.01)
Lubiprostone 8 µg bd Type-2 chloride channel activator Combined analysis of two 12-week phase 3 trials, n=1,171 Rome II (Drossman 2009, PMID 19006537) 17.9% vs 10.1% (p=0.001) overall responders on a 7-point global relief scale 53 (p=0.59)
Tegaserod 5-HT4 receptor agonist Withdrawn 2007, reintroduced after external adjudication; licensed for women <65 without cardiovascular ischaemic history See safety section 58 (p=0.03)
PEG 3350 + electrolytes Osmotic laxative 28-day RCT, n=139 (Chapman 2013, PMID 23835436) SBMs/week 4.40±2.58 vs 3.11±1.94 (95% CI of difference 1.17–1.95, p<0.0001); no improvement in abdominal discomfort/pain vs placebo —

Note the endpoint heterogeneity that makes cross-column comparison unsafe: linaclotide, tenapanor and plecanatide were judged on the FDA composite (≥30% worst-abdominal-pain reduction and ≥1 additional CSBM/week in the same week for ≥6 of 12 weeks); lubiprostone's registration used a patient-rated 7-point global relief question in a Rome II population. Placebo rates ranged from 10.1% to 23.7% across the same drug class, which alone can move an apparent NNT by a factor of two — see placebo-response-and-trial-design.

The comparative ranking

Fifteen RCTs, 8,462 patients, search to June 2018, all data extracted at 12 weeks (Black 2018, PMID 30144426):

Endpoint First-ranked
FDA composite responder Linaclotide 290 µg od
Each trial's own primary endpoint Linaclotide 290 µg od
Abdominal pain Linaclotide 290 µg od
Complete spontaneous bowel movements Linaclotide 290 µg od
Bloating Tenapanor 50 mg bd
Safety (fewest total adverse events) Plecanatide 6 mg od

Total adverse events were significantly greater than placebo for linaclotide (290 and 500 µg) and plecanatide 3 mg; diarrhoea was significantly more common with every drug except lubiprostone 8 µg bd; nausea was significantly more common with lubiprostone. The authors' own bottom line — "efficacy was similar among individual drugs and dosages for most end points" and "the long-term relative efficacy of these drugs is unknown" — is the correct reading of the ranking, which reflects P-scores rather than demonstrated superiority. Tenapanor was included and found superior to placebo; a 2025 systematic review of tenapanor trials examined FDA composite response, durability and risk of bias specifically (Al-Juhani 2025, PMID 41158898), and post-hoc analyses report abdominal-symptom improvement independent of change in CSBM frequency (Lembo 2024, PMID 38294158; Brenner 2025, PMID 39701047) — a claim that, if it holds, separates tenapanor's analgesic from its laxative action.

Uncoupling pain relief from secretion: the MD-7246 experiment

A phase 2b dose-ranging study randomised 532 IBS-C patients to placebo or one of seven linaclotide formulations — delayed-release targeting the ileum (DR1) or the ileocaecal junction and caecum (MD-7246, formerly DR2) at 30/100/300 µg, or immediate-release 290 µg — for 12 weeks. All DR1 and MD-7246 groups improved abdominal pain versus baseline and versus placebo. DR1 and IR improved CSBM frequency and composite responder rates; MD-7246 results for bowel endpoints were similar to placebo, and its diarrhoea rate matched placebo. The authors' interpretation: altering the site of intestinal delivery "might uncouple linaclotide's pain relief from secretory effects" (Chey 2021, PMID 33065589). This is the most direct evidence in the IBS-C literature that abdominal pain and constipation are pharmacologically separable — and it is consistent with the PEG result below, from the opposite direction.

Mechanistically, linaclotide accelerates colonic transit and raises caecal pH (Farmer 2019, PMID 30353623), so the secretory and motor effects are real; the question is whether they are what relieves pain.

Laxatives: bowel frequency without pain relief

PEG 3350 plus electrolytes beat placebo on spontaneous bowel movements in week 4 (4.40 ± 2.58 vs 3.11 ± 1.94/week; 95% CI 1.17–1.95, p<0.0001), on complete spontaneous bowel movements, responder rates, stool consistency and straining. Abdominal discomfort/pain improved versus run-in but not versus placebo (Chapman 2013, PMID 23835436). AGA gives PEG laxatives a conditional recommendation at low certainty (Chang 2022, PMID 35738724), and their place is essentially as a cheap first step that fixes the bowel habit and leaves the pain. Broader laxative guidance for chronic constipation is covered in dietetic guidelines (Dimidi 2025, PMID 41081513).

Tegaserod: withdrawal, adjudication, reintroduction

Tegaserod, a 5-HT4 agonist, was voluntarily withdrawn in 2007 on the basis of an internal adjudication of pooled placebo-controlled data suggesting a cardiovascular ischaemic signal. Two subsequent independent external adjudications of 18,645 patients (tegaserod 11,614; placebo 7,031) reported:

  • First adjudication: 14 events (0.075%) — tegaserod 13 (0.11%), placebo 1 (0.014%). All patients had ≥1 cardiovascular risk factor; 11 had ≥2.
  • Second adjudication: of 390 events reviewed, 24 (0.13%) classified as probable new or worsening — tegaserod 18 (0.16%), placebo 6 (0.09%). Coronary or cerebrovascular ischaemic events: 7 (0.06%) vs 1 (0.01%); OR 4.24, 95% CI 0.52–34.74, p=0.273.
  • Women <65 with no ischaemic history and ≤1 risk factor had no major adverse cardiovascular events (Lacy 2022, PMID 34048937).

The drug is now licensed in that restricted population. Two things are worth holding simultaneously: the point estimate for ischaemic events is a fourfold increase, and the confidence interval spans 0.52 to 34.74 — the data are compatible with substantial harm and with none. The episode is also a case study in regulatory decision-making under uncertainty, debated at the time (Brandt 2008, PMID 18477347; reviewed in Sayuk 2022, PMID 35123085).

Guideline positions

AGA's 2022 IBS-C guideline reviewed tenapanor, plecanatide, linaclotide, tegaserod, lubiprostone, PEG laxatives, tricyclics, SSRIs and antispasmodics and issued nine recommendations (Chang 2022, PMID 35738724):

Strength Certainty Agents
Strong for High Linaclotide
Conditional for Moderate Tenapanor, plecanatide, tegaserod, lubiprostone
Conditional for Low PEG laxatives, tricyclic antidepressants, antispasmodics
Conditional against Low SSRIs

ACG's guideline (Lacy 2021, PMID 33315591) and the BSG guideline (Vasant 2021, PMID 33903147) reach broadly compatible positions; divergences are catalogued on guidelines.

Safety, quantified

The 2026 safety meta-analysis (54 trials) converts adverse-event dropout into numbers needed to harm (Busam 2026, PMID 40471839):

Drug NNH for discontinuation due to adverse event p
Tenapanor 16 <0.01
Linaclotide 35 <0.01
Lubiprostone 53 0.59
Tegaserod 58 0.03
Plecanatide 59 <0.01
(Tricyclics, for comparison) 24 <0.01
(Rifaximin, for comparison) negative, non-significant —

Set against linaclotide's NNT of 5.1 (Chey 2012, PMID 22986437) and NNH of 35, the risk–benefit ratio for the best-evidenced agent is roughly 7:1 in favour — the most favourable ratio of any drug in this condition. Tenapanor's NNT-to-NNH ratio is much tighter. Diarrhoea caused discontinuation in 4.5% of linaclotide versus 0.2% of placebo patients (Chey 2012, PMID 22986437) and 6.5% versus 0.7% for tenapanor (Chey 2021, PMID 33337659). Long-term lubiprostone safety data extend to 52 weeks (Chey 2012, PMID 22251419).

What is missing

  • No head-to-head trial was retrieved between any two secretagogues in targeted PubMed and registry searches on 2026-09-02; the ranking is entirely indirect (Black 2018, PMID 30144426).
  • No placebo-controlled efficacy trial beyond 26 weeks was retrieved for the newer agents as of 2026-09-02. A 52-week open-label safety study exists for lubiprostone (Chey 2012, PMID 22251419), and a prospective observational study followed 202 adults starting linaclotide for 52 weeks; only 76 had paired 52-week IBS-SSS data, which improved by a mean −70.7 points (95% CI −95.0 to −46.5), without a randomized comparator (Yiannakou 2018, PMID 30302125). Long-term comparative efficacy therefore remains unresolved rather than wholly unstudied.
  • No validated predictor of response was retrieved in a targeted PubMed search on 2026-09-02. Baseline abdominal pain and bloating have been examined as modifiers for lubiprostone (Chang 2016, PMID 27669680), but they do not constitute a validated selection rule.
  • No drug-specific comparison against diet was retrieved in targeted PubMed and registry searches on 2026-09-02. CARIBS put "optimised medical treatment" at 58% response versus 76% for low-FODMAP plus dietary advice (Nybacka 2024, PMID 38643782), but did not report a secretagogue-specific comparison.

Open questions

  • Can pain relief be pharmacologically separated from secretion? MD-7246 improved pain without improving bowel endpoints (Chey 2021, PMID 33065589) and PEG improved bowel endpoints without improving pain versus placebo (Chapman 2013, PMID 23835436). No agent has been developed on that principle to registration.
  • Is linaclotide genuinely first, or first by P-score in a network where nothing differs (Black 2018, PMID 30144426)?
  • Is tegaserod safe? The adjudicated OR is 4.24 with a 95% CI of 0.52–34.74 (Lacy 2022, PMID 34048937); the restriction to low-risk women <65 is a precaution, not a demonstrated safety threshold.
  • Why does tenapanor rank first for bloating (Black 2018, PMID 30144426), and does that reflect its NHE3 mechanism or its higher discontinuation rate selecting tolerant responders?
  • What happens after 26 weeks (Chey 2012, PMID 22986437; Chey 2021, PMID 33337659)?
  • Should any secretagogue be started before a dietary trial, given CARIBS (Nybacka 2024, PMID 38643782)?

References

  1. Chang L, Sultan S, Lembo A, Verne GN, Smalley W, Heidelbaugh JJ. AGA Clinical Practice Guideline on the Pharmacological Management of Irritable Bowel Syndrome With Constipation. Gastroenterology. 2022;163(1):118-136. PMID 35738724
  2. Black CJ, Burr NE, Quigley EMM, Moayyedi P, Houghton LA, Ford AC. Efficacy of Secretagogues in Patients With Irritable Bowel Syndrome With Constipation: Systematic Review and Network Meta-analysis. Gastroenterology. 2018;155(6):1753-1763. PMID 30144426
  3. Chey WD, et al. Linaclotide for irritable bowel syndrome with constipation: a 26-week, randomized, double-blind, placebo-controlled trial. Am J Gastroenterol. 2012;107(11):1702-12. PMID 22986437
  4. Chey WD, Lembo AJ, Yang Y, Rosenbaum DP. Efficacy of Tenapanor in Treating Patients With Irritable Bowel Syndrome With Constipation: A 26-Week, Placebo-Controlled Phase 3 Trial (T3MPO-2). Am J Gastroenterol. 2021;116(6):1294-1303. PMID 33337659
  5. Brenner DM, et al. Efficacy, safety, and tolerability of plecanatide in patients with irritable bowel syndrome with constipation: results of two phase 3 randomized clinical trials. Am J Gastroenterol. 2018;113(5):735-745. PMID 29545635
  6. Drossman DA, Chey WD, Johanson JF, Fass R, Scott C, Panas R, Ueno R. Clinical trial: lubiprostone in patients with constipation-associated irritable bowel syndrome. Aliment Pharmacol Ther. 2009;29(3):329-41. PMID 19006537
  7. Chey WD, et al. Randomized Trial of 2 Delayed-Release Formulations of Linaclotide in Patients With Irritable Bowel Syndrome With Constipation. Am J Gastroenterol. 2021;116(2):354-361. PMID 33065589
  8. Chapman RW, Stanghellini V, Geraint M, Halphen M. Randomized clinical trial: macrogol/PEG 3350 plus electrolytes for treatment of patients with constipation associated with irritable bowel syndrome. Am J Gastroenterol. 2013;108(9):1508-15. PMID 23835436
  9. Lacy BE, Brenner DM, Chey WD. Re-evaluation of the Cardiovascular Safety Profile of Tegaserod: A Review of the Clinical Data. Clin Gastroenterol Hepatol. 2022;20(4):e682-e695. PMID 34048937
  10. Sayuk GS, Waldman SA, Brenner DM. Tegaserod: What's Old Is New Again. Clin Gastroenterol Hepatol. 2022;20(10):2175-2184.e19. PMID 35123085
  11. Brandt LJ. The FDA's decision-making process: isn't it time to temper the principle of protective paternalism? Am J Gastroenterol. 2008;103(5):1226-7. PMID 18477347
  12. Busam JA, et al. The Safety of Pharmacotherapy for Irritable Bowel Syndrome: A Systematic Review and Meta-Analysis. Am J Gastroenterol. 2026;121(3):745-753. PMID 40471839
  13. Chey WD, Drossman DA, Johanson JF, Scott C, Panas RM, Ueno R. Safety and patient outcomes with lubiprostone for up to 52 weeks in patients with irritable bowel syndrome with constipation. Aliment Pharmacol Ther. 2012;35(5):587-99. PMID 22251419
  14. Chang L, et al. Effects of baseline abdominal pain and bloating on response to lubiprostone in patients with irritable bowel syndrome with constipation. Aliment Pharmacol Ther. 2016;44(11-12):1114-1122. PMID 27669680
  15. Farmer AD, et al. Linaclotide increases cecal pH, accelerates colonic transit, and increases colonic motility in irritable bowel syndrome with constipation. Neurogastroenterol Motil. 2019;31(2):e13492. PMID 30353623
  16. Lembo AJ, et al. Abdominal Symptom Improvement During Clinical Trials of Tenapanor in Patients With Irritable Bowel Syndrome With Constipation: A Post Hoc Analysis. Am J Gastroenterol. 2024;119(5):937-945. PMID 38294158
  17. Brenner DM, et al. Tenapanor Improves Abdominal Symptoms Irrespective of Changes in Complete Spontaneous Bowel Movement Frequency in Adults with Irritable Bowel Syndrome with Constipation. Dig Dis. 2025;43(2):146-157. PMID 39701047
  18. Al-Juhani A, et al. Tenapanor for Irritable Bowel Syndrome With Constipation (IBS-C): A Systematic Review of Randomized Trials Assessing FDA Composite Response, Durability, and Risk-of-Bias. Cureus. 2025;17(9):e93337. PMID 41158898
  19. Markham A. Tenapanor: First Approval. Drugs. 2019;79(17):1897-1903. PMID 31677150
  20. Lacy BE, Pimentel M, Brenner DM, Chey WD, Keefer LA, Long MD, Moshiree B. ACG Clinical Guideline: Management of Irritable Bowel Syndrome. Am J Gastroenterol. 2021;116(1):17-44. PMID 33315591
  21. Vasant DH, et al. British Society of Gastroenterology guidelines on the management of irritable bowel syndrome. Gut. 2021;70(7):1214-1240. PMID 33903147
  22. Dimidi E, et al. British Dietetic Association Guidelines for the Dietary Management of Chronic Constipation in Adults. J Hum Nutr Diet. 2025;38(5):e70133. PMID 41081513
  23. Nybacka S, et al. A low FODMAP diet plus traditional dietary advice versus a low-carbohydrate diet versus pharmacological treatment in irritable bowel syndrome (CARIBS). Lancet Gastroenterol Hepatol. 2024;9(6):507-520. PMID 38643782
  24. Yiannakou Y, et al. UK clinical experience up to 52 weeks with linaclotide for irritable bowel syndrome with constipation. Therap Adv Gastroenterol. 2018;11:1756284818798791. PMID 30302125