Is linaclotide FDA-approved, and what does the research show?

What is linaclotide?

Linaclotide is a peptide of 14 amino acids ¹. A peptide is a short chain of amino acids, the building blocks of proteins. The label says it is "structurally related to human guanylin and uroguanylin," two peptides the body makes itself ¹.

It belongs to a drug class called guanylate cyclase-C agonists ¹. Guanylate cyclase-C, or GC-C, is a receptor on the surface of the cells that line the intestine, and an agonist is a drug that switches a receptor on ¹. AbbVie and Ironwood Pharmaceuticals market it in the United States as Linzess, a capsule taken by mouth ¹. It is a digestive medicine, not a wellness, weight or performance peptide. The label's uses are bowel conditions, and it lists nothing for weight, muscle, aging or performance ¹.

Is linaclotide FDA-approved?

Yes. FDA approved linaclotide as Linzess, a prescription medicine, with initial U.S. approval in 2012 ¹. FDA approved NDA 202811, the new drug application filed by Forest Laboratories and now held by AbbVie, on August 30, 2012, with marketing status "Prescription" for all three capsule strengths ². The 2012 approval covered "irritable bowel syndrome with constipation" and "chronic idiopathic constipation," and the first label limited both uses to adults ², ³.

"Idiopathic" means the cause of the constipation is unknown, the Medication Guide explains ¹. In the label's adult trials, IBS-C meant abdominal pain with fewer than three complete bowel movements a week ¹. Chronic idiopathic constipation meant fewer than three spontaneous bowel movements a week, with straining, hard stools or a sense of incomplete emptying ¹.

FDA then added three uses for children, each by a supplement with its own approval letter ². Functional constipation in children aged 6 to 17 was added on June 12, 2023 ². Irritable bowel syndrome with constipation in children aged 7 and older followed on November 4, 2025 ². Functional constipation was extended down to age 2 on May 21, 2026 ². Drugs@FDA also lists three generic applications for linaclotide capsules as of November 9, 2026, one with marketing status "Prescription" and two "Discontinued" ².

The current label, revised in October 2026, and FDA's own copy of May 2026 list three uses: "irritable bowel syndrome with constipation (IBS-C) in adults and pediatric patients 7 years of age and older," "chronic idiopathic constipation (CIC) in adults," and "functional constipation (FC) in pediatric patients 2 years of age and older" ¹, ⁷. The label does not define functional constipation; in its pediatric trials it meant fewer than three spontaneous bowel movements a week with stool withholding, painful or hard stools, or soiling ¹. A clinician's prescription is the only route to it ², ¹.

See the FDA status of every peptide, updated weekly.

How does linaclotide work?

Linaclotide, and the active form the gut breaks it into, bind to GC-C ¹. They "act locally on the luminal surface of the intestinal epithelium," the label says, meaning on the inner lining of the gut ¹. Switching on GC-C raises a messenger molecule, cyclic GMP, inside and outside the lining cells ¹. The rise inside the cells makes them secrete chloride and bicarbonate into the bowel ¹. That draws in fluid and speeds the passage of stool ¹.

In an animal model of visceral pain, the label adds, linaclotide also reduced abdominal muscle contraction and the activity of pain-sensing nerves ¹. It attributes that effect to cyclic GMP outside the cells ¹.

The drug barely enters the blood. The label calls it "minimally absorbed with negligible systemic availability," and neither linaclotide nor its active form could be measured in plasma after the recommended doses ¹. It is broken down inside the gut into smaller peptides and amino acids ¹. The label, not a trial, is the source of this account; the pain effect rests on an animal model, the bowel effect on trials in people ¹. Plecanatide, sold as Trulance, is the other approved drug in this class and has its own page.

What does the research show?

FDA approved linaclotide on randomized, placebo-controlled trials in adults and then in children, the top of the evidence scale ¹, ². A placebo-controlled trial compares the drug with an identical dummy capsule. The difference between the groups is then the drug's effect. The trials below enrolled people with a diagnosed bowel disorder ⁴, ⁵, ⁸, ⁶. Their results belong to those populations.

Studied in people with IBS-C: two phase 3, double-blind, placebo-controlled trials, both published in November 2012 ⁴, ⁸. Phase 3 is the last stage of testing before approval, and double-blind means neither patients nor doctors knew who had the drug. Each randomized about 800 adults, and both used FDA's responder endpoint, the trial's measure of success ⁴, ⁸.

A patient met it by reporting at least a 30 percent fall in worst abdominal pain and at least one more complete spontaneous bowel movement a week ⁴. Both had to fall in the same week, for at least 6 of 12 weeks ⁴. A complete spontaneous bowel movement is one passed without a laxative that leaves a sense of complete emptying ¹.

In the 26-week trial, 804 patients were evaluated, mean age 44 and 90 percent women ⁴. Over the first 12 weeks, 33.7 percent on linaclotide met the FDA endpoint against 13.9 percent on placebo ⁴. That is a number needed to treat of 5.1, about five patients treated for one extra responder ⁴. Its 95 percent confidence interval, the range the true figure most likely lies in, was 3.9 to 7.1 ⁴.

The pain criterion was met by 48.9 percent against 34.5 percent, and the bowel-movement criterion by 47.6 percent against 22.6 percent ⁴. The differences from placebo held across the full 26 weeks, and diarrhea led 4.5 percent on linaclotide to stop treatment against 0.2 percent on placebo ⁴.

In the 12-week trial of 800 patients, 136 of 405 on linaclotide (33.6 percent) met the FDA endpoint against 83 of 395 on placebo (21.0 percent) ⁸. When patients on linaclotide were switched to placebo for a further four weeks, symptoms returned but did not worsen beyond baseline ⁸. FDA's label reports the same two trials as Trials 1 and 2 ¹. It adds a stricter bar of response in 9 of 12 weeks with at least three complete bowel movements a week ¹. On that bar, 12 percent responded against 5 percent in one trial, and 13 against 3 in the other ¹.

A third adult trial in the label, Trial 6, randomized 614 adults with IBS-C for 12 weeks with a combined score of bloating, discomfort and pain as its primary endpoint ¹. On a 0-to-10 scale, the score fell by 1.9 points on linaclotide and 1.2 on placebo, a difference of 0.7 (95 percent confidence interval 0.4 to 1.0) ¹.

Studied in people with chronic constipation: two randomized, 12-week, double-blind, placebo-controlled trials, published in August 2011 ⁵. They enrolled 1,276 adults between them ⁵.

The primary endpoint was at least three complete spontaneous bowel movements a week, and at least one more than at baseline, in at least 9 of the 12 weeks ⁵. The lower-dose arms reached it in 21.2 and 16.0 percent of patients, and the higher-dose arms in 19.4 and 21.3 percent ⁵. The placebo arms reached it in 3.3 and 6.0 percent ⁵. Diarrhea led 4.2 percent of patients in both linaclotide groups to stop ⁵. The authors wrote that "additional studies are needed to evaluate the potential long-term risks and benefits" ⁵.

FDA's label reports these as Trials 3 and 4 and presents only the approved dose ¹. The higher dose, it says, "did not consistently offer additional clinically meaningful treatment benefit" over the lower one ¹.

A fifth adult trial, Trial 5, randomized 1,223 adults with chronic idiopathic constipation to a still lower dose, the approved dose or placebo for 12 weeks ¹. Responder rates were 13 percent against 5 percent ¹. In the label's open-label extension trials, where everyone knew who had the drug, 2,147 patients with IBS-C and 1,129 with chronic constipation took linaclotide for up to 18 months ¹. About 29 and 27 percent of them had the dose reduced or suspended for adverse reactions, most of them diarrhea or other gut effects ¹.

Studied in children with functional constipation: a phase 3, double-blind, placebo-controlled trial, published online in January 2024 ⁶. It randomized 330 children aged 6 to 17 at 64 sites in seven countries ⁶. Efficacy and safety were analyzed in 164 per group ⁶.

Spontaneous bowel movements rose by 2.22 a week on linaclotide and 1.05 on placebo, from about 1.2 a week at baseline ⁶. The paper reports the gain over placebo as 1.17 a week, with a 95 percent confidence interval of 0.65 to 1.69 ⁶. FDA's label, reporting the same trial as Trial 7, gives its own figures: a difference of 1.3 a week (0.7 to 1.8) ¹.

Stool consistency also improved, and 89 percent of the children completed the 12 weeks ⁶. The trial was funded by AbbVie and Ironwood Pharmaceuticals, the drug's makers ⁶.

Two smaller pediatric trials sit in the label. In children aged 7 to 17 with IBS-C, Trial 8 randomized 108 patients to the approved dose or a higher one, with no placebo arm described ¹. Of the 53 evaluated on the approved dose, 16 (30 percent) met the combined responder endpoint ¹. In children aged 2 to 5 with functional constipation, Trial 9 compared 62 on linaclotide with 61 on placebo over 12 weeks ¹. Bowel movements rose by 2.1 a week against 1.4, a difference of 0.7 (95 percent confidence interval 0.03 to 1.31) ¹.

No trial among this page's sources, as of November 10, 2026, studied linaclotide for anything but constipation and IBS-C ⁴, ¹, ⁵, ⁸, ⁶. None ran a blinded comparison beyond 26 weeks ⁴, ¹, ⁵, ⁸, ⁶.

What are the side effects?

Diarrhea leads, and the label documents it in every population. In the two pooled adult IBS-C trials, 807 patients took linaclotide and 798 took placebo ¹. Diarrhea was reported by 20 percent against 3 percent, abdominal pain by 7 against 5, and flatulence by 4 against 2 ¹. Abdominal distension, or bloating, was reported by 2 against 1, viral gastroenteritis by 3 against 1, and headache by 4 against 3 ¹.

Severe diarrhea occurred in 2 percent against less than 1, and 5 percent stopped treatment because of diarrhea against less than 1 percent on placebo ¹. Most cases began within the first two weeks ¹. In all, 9 percent on linaclotide and 3 percent on placebo stopped for adverse reactions ¹.

In the two chronic constipation trials, with 430 on the approved dose and 423 on placebo, diarrhea was reported by 16 percent against 5 ¹. In Trial 5, at the lowest dose, it was 19 percent against 7 ¹.

In children aged 6 to 17 with functional constipation, diarrhea was reported by 4 percent against 2 percent on placebo ¹. One 17-year-old on linaclotide had severe diarrhea with dehydration and was admitted to hospital; the case resolved with intravenous fluids ⁶. In children aged 7 to 17 with IBS-C, 7 percent of those on the approved dose reported diarrhea ¹. Among 62 children aged 2 to 5, one had mild diarrhea that resolved on treatment ¹.

Since approval, the label says, "severe diarrhea associated with dizziness, syncope, hypotension and electrolyte abnormalities (hypokalemia and hyponatremia) requiring hospitalization or intravenous fluid administration have been reported" ¹. Syncope is fainting, hypotension low blood pressure, and hypokalemia and hyponatremia low potassium and low sodium in the blood. Post-marketing reports also include anaphylaxis and angioedema, severe allergic reactions and swelling beneath the skin, as well as rash, nausea, blood in the stool and rectal bleeding ¹. If severe diarrhea occurs, the label tells prescribers to suspend the drug and rehydrate the patient ¹.

The label carries a boxed warning at its head, "RISK OF SERIOUS DEHYDRATION IN PEDIATRIC PATIENTS LESS THAN 2 YEARS OF AGE" ¹. It reads: "LINZESS is contraindicated in patients less than 2 years of age; in nonclinical studies in neonatal mice, administration of a single, clinically relevant adult oral dose of linaclotide caused deaths due to dehydration" ¹. The 2012 label had set that line at "pediatric patients up to 6 years of age" ³. The line moved to 2 in August 2021, when a revised label listed the boxed warning among its recent major changes ⁹. By the current label the line stands at 2 ¹.

The label's two contraindications are children under 2 and "known or suspected mechanical gastrointestinal obstruction," a physical blockage of the gut ¹. It also warns that accidental ingestion by a child, above all one under 2, "may result in severe diarrhea and dehydration" ¹. Patients are told to store the capsules out of children's reach ¹.

On pregnancy, the label says linaclotide is "negligibly absorbed," so maternal use "is not expected to result in fetal exposure" ¹. The human data, it adds, are too few to judge the risk of birth defects or miscarriage ¹. It was not detected in the breast milk of mothers taking it ¹. In two-year studies it did not cause tumors in rats or mice ¹.

In sport

Linaclotide is not named on WADA's 2026 Prohibited List, and neither are guanylate cyclase-C agonists as a class ¹⁰. WADA is the World Anti-Doping Agency. Its list covers peptide hormones and their mimetics in section S2 and hormone and metabolic modulators in S4, and names neither linaclotide nor its brand in either ¹⁰.

What JumpstartMD offers

JumpstartMD does not prescribe linaclotide. Our peptide library covers it so you have the facts on its FDA status and the evidence, current as of November 10, 2026.

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Compounded medications are not FDA-approved, and FDA does not review their safety, effectiveness, or quality before they are marketed. A licensed clinician decides after an evaluation whether a peptide is appropriate for you, and not every patient will qualify.