Evidence Grade A — Regulatory approved. 458 published studies. 58 registered clinical trials.
Medically reviewed by a licensed medical professional
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Linaclotide (sold as Linzess) is a daily oral capsule for irritable bowel syndrome with constipation (IBS-C) and chronic constipation. It works directly in the gut to increase fluid secretion (softening stool) and reduce the abdominal pain and bloating that characterise IBS. Because it barely enters the bloodstream, it acts almost entirely within the intestine with minimal whole-body side effects.
Linaclotide is also known by these brand and alternate names:
458 published studies: 321 human, 16 animal, 14 in-vitro, 184 reviews
Linaclotide is marketed as Linzess (approved August 2012). It is taken as a daily oral capsule on an empty stomach, at least 30 minutes before the first meal. The recommended dose is 290 mcg for IBS-C and 72 or 145 mcg for chronic constipation.
In clinical trials, approximately 34% of IBS-C patients met the composite improvement endpoint compared to 17% on placebo. Diarrhoea is the most common side effect (approximately 20%) and the leading reason for discontinuation. Linaclotide has a boxed warning against use in children under 6 years due to deaths in young mice, though no such events have been reported in humans. It competes with plecanatide (which targets the same pathway) and other IBS-C treatments.
Linaclotide works on the inner lining of the intestine in two ways. First, it activates receptors (GC-C) that trigger chloride and water secretion into the gut, softening stool and accelerating transit. Second, the same signalling pathway reduces the sensitivity of pain-sensing nerves in the gut wall, decreasing the visceral hypersensitivity that causes abdominal pain in IBS. Because the peptide is broken down in the gut and barely enters the bloodstream, systemic side effects are minimal — the main side effect is diarrhoea, which is essentially the intended mechanism working too effectively.
Clinical trials showed that about 34% of IBS-C patients met the combined improvement endpoint (reduced pain and improved bowel function) compared to 17% on placebo. The dual mechanism — both increasing fluid secretion and reducing visceral pain sensitivity — distinguishes linaclotide from simple laxatives. Diarrhoea is the most common side effect (approximately 20%) and the main reason patients stop treatment — essentially, the intended mechanism sometimes works too well. The drug carries a boxed warning against use in children under 6 after deaths in young mice, though no such events have occurred in humans. It must be taken on an empty stomach at least 30 minutes before the first meal of the day. Generic availability has improved access. A paediatric approval for functional constipation was recently granted, and there is ongoing research into whether GC-C pathway activation might help prevent colorectal cancer.
PeptideTrace tracks 58 registered clinical trials for Linaclotide sourced from ClinicalTrials.gov.
Proof of Principle Study for an Efficacy Trial of Linaclotide for Cystic Fibrosis
"Efficacy and Safety of Linaclotide in Chronic Constipation"
Linaclotide for Colonoscopy Bowel Prep
Clinical Study on the Application of Lactulose Combined with Linaclotide in Bowel Preparation for Colonoscopy
A Study of Virtual Reality and Linaclotide for IBS-C
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Linaclotide is a 14-amino-acid peptide with 3 intramolecular disulfide bonds (Cys1-Cys6, Cys2-Cys10, Cys5-Cys13), making it structurally rigid and resistant to proteolytic degradation. It is structurally related to the endogenous guanylin/uroguanylin peptides that regulate intestinal fluid secretion.
Linaclotide has a dual mechanism of action. (1) Secretory: It binds guanylate cyclase-C (GC-C) receptors on the luminal surface of intestinal epithelial cells, increasing intracellular cGMP production. cGMP activates the CFTR chloride channel, driving chloride, bicarbonate, and water secretion into the intestinal lumen, accelerating transit. (2) Analgesic: Extracellular cGMP released into the submucosa inhibits colonic nociceptor firing, reducing visceral hypersensitivity—this addresses the pain component of IBS. Minimal systemic absorption occurs; it acts locally in the GI tract.
Linaclotide is marketed as Linzess (Ironwood/AbbVie, approved August 30, 2012). Indicated for IBS-C (290 mcg daily) and CIC (72 mcg or 145 mcg daily). In pooled IBS-C trials, the FDA composite responder rate was 33.7% versus 17.4% for placebo (P<0.0001). The most common adverse event is diarrhea (~20% in IBS-C trials). Linaclotide must be taken on an empty stomach (30 minutes before first meal). Generic linaclotide became available in 2023.
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Octreotide is marketed as Sandostatin (approved 1988), Sandostatin LAR monthly depot (approved 1998), and Mycapssa oral capsules (approved June 2020 — the first oral somatostatin analogue). It is used for acromegaly, carcinoid syndrome, VIPomas, and gastroenteropancreatic neuroendocrine tumours (GEP-NETs). The PROMID trial demonstrated that octreotide LAR significantly delayed tumour progression in patients with neuroendocrine tumours of the midgut, establishing somatostatin analogues as a standard treatment for these cancers. The approval of Mycapssa as an oral formulation was a significant advance for patients who had been receiving monthly injections for years. Octreotide has been on the market for over 35 years and has one of the longest safety track records of any peptide medication.
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