Linaclotide and Plecanatide: How the Guanylate Cyclase-C Peptides Treat Chronic Constipation and IBS-C

Linaclotide and plecanatide are two of the few peptide drugs that you swallow rather than inject, and they work precisely because they barely leave your gut. Both are guanylate cyclase-C (GC-C) agonists, which means they copy your body's own intestinal peptides guanylin and uroguanylin, switch on a receptor lining the intestine, and pull salt and water into the bowel. Linaclotide is sold as Linzess and plecanatide as Trulance, and both are FDA approved for chronic idiopathic constipation (CIC) and irritable bowel syndrome with constipation (IBS-C) in adults.

That makes the GC-C peptides a useful case study if you are interested in how peptide drugs really work. They show how an oral peptide can succeed when its target sits on the inside surface of the intestine, and their large phase 3 programs give a far clearer picture of benefit and side effects than most peptides you will read about online. This article explains the mechanism, what the main trials found, how the two drugs compare and what the labels warn about. It is educational content about published research, not medical advice, and these are prescription medicines that belong with a clinician who knows your history.

Linaclotide and plecanatide are short synthetic peptides that activate guanylate cyclase-C, a receptor on the cells lining your intestine. The Linzess label describes linaclotide as structurally related to human guanylin and uroguanylin and as a GC-C agonist, while the Trulance label calls plecanatide a structural analog of human uroguanylin (Linzess prescribing information (DailyMed, revised 5/2026); Trulance prescribing information (DailyMed, updated April 2024)).

Guanylin and uroguanylin are peptides your gut makes for itself to regulate fluid balance, and linaclotide and plecanatide borrow that signaling system and turn it up. Because you take them by mouth as a capsule or tablet, they are an exception to the usual rule that peptide drugs need an injection, which our guide to oral vs injectable peptides explains in more depth.

The two drugs share the same adult indications but differ in children. The current Linzess label lists IBS-C in adults and in children 7 years of age and older, CIC in adults, and functional constipation in children 2 years of age and older, whereas the Trulance label lists CIC and IBS-C in adults only.

Guanylate cyclase-C agonists work by raising a messenger molecule called cyclic GMP (cGMP) inside intestinal cells, which pushes chloride and bicarbonate out into the gut and draws water after them. Both labels describe the same chain of events: elevation in intracellular cGMP stimulates secretion of chloride and bicarbonate into the intestinal lumen, mainly through activation of the cystic fibrosis transmembrane conductance regulator (CFTR) ion channel.

The extra fluid softens stool and speeds its passage, which is why this drug class is sometimes grouped with other secretagogues, medicines that increase intestinal secretion rather than acting as bulk or stimulant laxatives.

Linaclotide's label suggests that cGMP may also influence pain signaling, but that evidence comes from animals. In an animal model of visceral pain, the label states, linaclotide reduced abdominal muscle contraction. The IBS-C trials in people measured pain directly, and those results are covered below, but the mechanism behind any pain benefit in humans has not been established in trials.

Minimal absorption matters because it keeps the drug's action inside your intestine. The Linzess label states that linaclotide is minimally absorbed with negligible systemic availability following oral administration, and the Trulance label says the same of plecanatide. GC-C receptors sit on the inner surface of the gut, so the peptide never needs to reach your bloodstream to work, and this is also why the main side effect is a local one: diarrhea.

Linaclotide clearly outperformed placebo in chronic constipation, although most patients did not reach the strict main endpoint. Lembo and colleagues reported two randomized 12 week trials (Trials 303 and 01) involving 1276 patients with chronic constipation, who took placebo or linaclotide 145 μg or 290 μg once daily (New England Journal of Medicine, 2011, doi.org/10.1056/NEJMoa1010863).

The primary endpoint was demanding, since it required three or more complete spontaneous bowel movements (CSBMs) per week plus an increase of at least 1 from baseline, during at least 9 of the 12 weeks.

For Trials 303 and 01 respectively, the endpoint was reached by 21.2% and 16.0% of patients on 145 μg and by 19.4% and 21.3% on 290 μg, compared with 3.3% and 6.0% on placebo. All secondary endpoints also improved more on linaclotide, and diarrhea was the one adverse event that stood out, leading to discontinuation of treatment in 4.2% of patients in both linaclotide groups.

In IBS-C, linaclotide improved both abdominal pain and bowel movements over 26 weeks. Chey and colleagues randomized IBS-C patients to placebo or linaclotide 290 μg once daily in a phase 3 trial that evaluated 804 patients, with a mean age of 44 and 90% female (American Journal of Gastroenterology, 2012, doi.org/10.1038/ajg.2012.254).

The trial used the FDA's IBS-C responder definition, which counts you as a responder only if you report at least 30% improvement in average daily worst abdominal pain and an increase of at least 1 CSBM from baseline, both in the same week, for at least 6 of 12 weeks.

On that combined endpoint, 33.7% of linaclotide patients responded versus 13.9% on placebo, which works out to a number needed to treat of 5.1. Looking at the two components separately, the pain criterion was met by 48.9% versus 34.5%, and the CSBM criterion by 47.6% versus 22.6%. Diarrhea caused discontinuation in 4.5% of linaclotide patients versus 0.2% on placebo.

Plecanatide produced results in the same range as linaclotide, again with diarrhea as the most common side effect. Miner and colleagues randomized 1,394 patients with CIC to plecanatide 3 mg, 6 mg or placebo once daily for 12 weeks (American Journal of Gastroenterology, 2017, doi.org/10.1038/ajg.2016.611), and durable overall CSBM responders were 21.0% on 3 mg and 19.5% on 6 mg, compared with 10.2% on placebo.

Mean weekly CSBMs rose by 2.5 and 2.2 per week on the two doses versus 1.2 per week on placebo, and spontaneous bowel movements rose by 3.2 and 3.1 per week versus 1.3. Diarrhea occurred in 1.3% on placebo, 5.9% on 3 mg and 5.7% on 6 mg. The trial was funded by the drug's developer, Synergy Pharmaceuticals, which also employed several of the authors.

Plecanatide also beat placebo in IBS-C across two separate trials. Brenner and colleagues ran two identical phase 3 trials that randomized 2189 adults with IBS-C to placebo or plecanatide 3 or 6 mg for 12 weeks, using the same FDA responder definition (American Journal of Gastroenterology, 2018, doi.org/10.1038/s41395-018-0026-7).

In Study 1, overall responders were 30.2% and 29.5% on 3 and 6 mg versus 17.8% on placebo, and in Study 2 they were 21.5% and 24.0% versus 14.2%. Diarrhea occurred in 4.3% on 3 mg, 4.0% on 6 mg and 1.0% on placebo, and discontinuation because of diarrhea was 1.2%, 1.4% and 0 respectively.

Nobody knows for certain, because no trial has compared the two drugs head to head. The best available evidence comes from network meta analyses, which compare drugs indirectly through their placebo controlled trials.

Black and colleagues pooled 15 randomized trials including 8462 patients with IBS-C (Gastroenterology, 2018, doi.org/10.1053/j.gastro.2018.08.021). Linaclotide 290 μg once daily ranked first for efficacy on the FDA endpoint, while plecanatide 6 mg once daily ranked first for safety. The authors concluded that efficacy was similar among individual drugs and dosages for most end points, and they noted that data were extracted at 12 weeks, so the long term relative efficacy of these drugs is unknown.

For chronic idiopathic constipation, Luthra and colleagues analyzed 33 randomized trials comprising 17 214 patients (Lancet Gastroenterology & Hepatology, 2019, doi.org/10.1016/S2468-1253(19)30246-8). Almost all drugs were superior to placebo, and prucalopride 2 mg ranked first at 12 weeks on one endpoint, while on another endpoint linaclotide 290 μg and prucalopride 2 mg had similar efficacy. That 290 μg dose is above the 145 mcg the current Linzess label recommends for adult CIC.

The labels do show lower diarrhea rates for plecanatide, but those figures come from separate trials and should not be read as a direct comparison. The Linzess label reports diarrhea in 20% of linaclotide patients versus 3% on placebo in the IBS-C trials, and 16% on 145 mcg versus 5% on placebo in the CIC trials. The Trulance label reports diarrhea of 5% versus 1% in CIC and 4.3% versus 1% in IBS-C, with severe diarrhea in 0.6% versus 0.3% in CIC and 1% versus 0.1% in IBS-C.

Different trial populations, endpoints and ways of collecting side effects all affect these numbers, so it is safest to treat the gap as a hypothesis rather than a settled difference.

Current guidelines treat both GC-C agonists as established options for chronic idiopathic constipation. The 2023 joint clinical practice guideline from the American Gastroenterological Association and the American College of Gastroenterology agreed on 10 recommendations and made strong recommendations for polyethylene glycol, sodium picosulfate, linaclotide, plecanatide and prucalopride for CIC in adults (Chang and colleagues, Gastroenterology, 2023, doi.org/10.1053/j.gastro.2023.03.214).

The guideline panel also emphasized shared decision making based on patient preferences, medication cost and availability. Over the counter options such as polyethylene glycol sit alongside the prescription peptides in that strong recommendation group, which is one reason the GC-C agonists are not automatically first in line.

The labeled doses are fixed once daily amounts that differ by drug and condition, and the table below sets them out as the labels state them. The right choice depends on your diagnosis, your other medications and how you tolerate the first weeks, which is a conversation for your prescriber, and our overview of peptide side effects for beginners covers how to think about tolerability more generally.

Both labels carry a boxed warning about serious dehydration in young children, but the age limits now differ. The Linzess label states that it is contraindicated in patients less than 2 years of age because, in nonclinical studies in neonatal mice, a single, clinically relevant adult oral dose of linaclotide caused deaths due to dehydration. The Trulance label contraindicates use in patients less than 6 years of age and advises avoiding it from 6 years to less than 18 years of age. Both labels also contraindicate use at any age in people with known or suspected mechanical gastrointestinal obstruction.

Linaclotide now has some pediatric trial data behind it. In a 4 week phase 2 study of 101 children aged 7 to 17 with IBS-C, linaclotide was tolerated well and showed numerical improvement in spontaneous bowel movement frequency compared with placebo (Di Lorenzo and colleagues, Journal of Pediatric Gastroenterology and Nutrition, 2024, doi.org/10.1002/jpn3.12103). That study was small and short, so its results should be treated as preliminary.

The GC-C agonists matter to peptide research because they prove a point that is often overlooked, which is that an oral peptide can be a thoroughly tested drug when its target is in the gut. Most peptides discussed online, from BPC-157 to the growth hormone secretagogues, have little or no phase 3 evidence, whereas linaclotide and plecanatide have several thousand trial participants behind them, published primary endpoints and labels reviewed by a regulator.

They also show the tradeoff that comes with real data. Responder rates that sit well short of a majority, against placebo responses that are not trivial, are what a proven gut peptide looks like in practice, and that is a useful benchmark to keep in mind when a less studied peptide is promised to do far more. If you are interested in the gut more broadly, our gut microbiome beginner's guide is a useful companion.

Linaclotide and plecanatide are prescription GC-C agonists that act locally in your intestine, and in large phase 3 trials both improved bowel movements, and in IBS-C abdominal pain, more often than placebo. No trial has compared them directly, network meta analyses find their efficacy broadly similar, and diarrhea is the side effect to expect with either. If constipation or IBS-C is affecting your life, these are well documented options to raise with a gastroenterologist or primary care clinician, alongside the over the counter treatments that guidelines rate just as highly.