Larazotide

AT-1001 · INN-202 · Larazotide acetate · Octapeptide zonulin inhibitor

"The most studied tight-junction regulator in the peptide space. Originally a celiac-disease adjunct (Phase 3 discontinued 2022). Now investigated in gut-barrier dysfunction, post-COVID inflammation, and MIS-C. Excellent safety record across thousands of trial subjects."

Type

8-amino-acid synthetic peptide · oral

Origin

Fasano group · derived from V. cholerae Zot toxin

Status

UK: not illegal to buy or possess · WADA: not specifically listed · US FDA: Phase 3 celiac discontinued 2022 · Phase 2 ongoing other indications

Primary use

Gut barrier / tight junction integrity

Protocol summary

Trial dose

0.5 mg before meals (3× daily)

Route

Oral capsule · pre-meal

Cycle

Continuous · symptom-driven

Clinical-trial

0.25–1 mg three times daily, taken 15 min before meals containing gluten or known triggers

Phase 2/3 dosing in celiac trials. Oral bioavailability is low — that's by design (acts in gut lumen, not systemic).

How we read the evidence

Largest safety dataset of any zonulin-pathway peptide · Phase 3 celiac program discontinued 2022 (efficacy threshold not met) · newer Phase 2 data in MIS-C and post-COVID inflammation · genuinely strong mechanistic foundation

Phase 3 celiac program (discontinued 2022) — what actually happened

9 Meters Biopharma ran the CeDLara Phase 3 trial of Larazotide in non-responsive celiac disease (patients with persistent symptoms despite a gluten-free diet). In June 2022, the company announced discontinuation after the trial did not meet the primary efficacy endpoint at the planned interim analysis. Safety was not the issue — the compound's tolerability profile was strong throughout. The discontinuation reflects efficacy in that specific patient population at the doses tested, not a broader failure of the zonulin-antagonist mechanism. Several Phase 2 programs in other indications continued.

Phase 2a MIS-C trial (Sci Transl Med, 2024) — positive proof-of-concept

Mass General published a Phase 2a randomized, double-blind, placebo-controlled trial in 12 children with post-COVID Multisystem Inflammatory Syndrome (MIS-C). Adjuvant Larazotide four times daily for 3 weeks showed faster clearance of circulating SARS-CoV-2 spike protein (within 1 day vs 10 days for controls) and shorter time to recovery. Small sample, but the proof-of-concept is meaningful: a gut-permeability regulator improving a systemic post-viral inflammatory syndrome supports the broader "leaky gut → systemic inflammation" hypothesis at clinical-trial level for the first time.

Mechanistic + preclinical foundation — substantial

Larazotide is a synthetic octapeptide (H-Gly-Gly-Val-Leu-Val-Gln-Pro-Gly-OH) derived from the active region of Vibrio cholerae's zonula occludens toxin. It acts as a zonulin antagonist, blocking zonulin-induced opening of intestinal tight junctions. More recent work links its activity to inhibition of myosin light chain kinase, which reduces actin filament tension and facilitates tight junction closure. Animal models (rodent and porcine) consistently show reduced gut permeability, improved barrier function, and reduced systemic inflammation. The mechanism is biologically coherent and the preclinical base is reproducible across multiple groups — not single-source.

Convergence

Larazotide has the cleanest safety record of any peptide in this category — thousands of trial subjects across Phase 1 / 2 / 3, mild headache the most-reported event. The mechanism is well-characterised and reproducible. The Phase 3 celiac efficacy miss matters for that specific indication; it doesn't invalidate the broader mechanism. The MIS-C Phase 2a result is small but suggests the zonulin pathway is a real clinical target beyond celiac. For Pep IQ's audience — gut barrier dysfunction, IBS, post-viral inflammation, leaky-gut protocols — Larazotide is the most evidence-grounded tool currently available, with the strongest tolerability data of any option in this lane.

Origin & Background

From cholera toxin to zonulin antagonist

Larazotide (AT-1001) was developed by the Alessio Fasano group, originally at the University of Maryland and later through Alba Therapeutics, Innovate Biopharmaceuticals, and 9 Meters Biopharma. Its origin is unusual: the active sequence was derived from the zonula occludens toxin (Zot) produced by Vibrio cholerae, the bacterium responsible for cholera. Zot disrupts intestinal tight junctions to facilitate fluid loss — Fasano's group identified the receptor-binding region and engineered an antagonist version that occupies the same receptor without opening junctions.

That receptor pathway is the zonulin pathway. Zonulin is an endogenous human protein involved in regulating intestinal barrier permeability. Elevated zonulin signalling has been documented in celiac disease, type 1 diabetes, and a growing list of autoimmune and inflammatory conditions where compromised gut barrier function appears to play an upstream role. Larazotide blocks this signalling — without crossing into systemic circulation in any meaningful quantity. It acts in the gut lumen and gets eliminated.

The clinical development arc: Phase 1 and 2 trials demonstrated excellent tolerability across hundreds of subjects. The Phase 3 CeDLara program in non-responsive celiac disease ran until 2022, when 9 Meters Biopharma announced discontinuation following an interim efficacy analysis. The mechanism was not the issue — the dose-response in that specific patient population did not reach the regulatory threshold. Phase 2 programs in other indications (MIS-C, IBS) continued and have produced positive proof-of-concept data.

Why this compound matters beyond celiac: The Phase 3 celiac result was specific to non-responsive celiac and the doses tested. The zonulin pathway itself is a credible upstream regulator in many inflammatory conditions where gut barrier dysfunction precedes systemic inflammation. The 2024 Mass General MIS-C trial demonstrated this at small scale — gut-permeability modulation shortening clearance of a viral antigen circulating in blood. The broader hypothesis (leaky gut → systemic inflammation → autoimmunity / chronic disease) gets clinical-trial support from results like this.

Science & Mechanism

A tight junction regulator, not a destroyer

Mechanism of Action

Zonulin receptor antagonism: Larazotide competes with endogenous zonulin for binding to the EGFR / PAR2 receptor complex on intestinal epithelium. By occupying the receptor without triggering it, larazotide blocks zonulin's downstream signal to disassemble tight junctions.

Myosin light chain kinase inhibition: More recent mechanistic work links larazotide to inhibition of MLCK, which reduces actin filament contraction at the apical pole of epithelial cells. This relaxes the tension that pulls tight junction proteins apart and allows them to reseal.

Tight junction protein redistribution: Imaging studies show larazotide treatment promotes the relocalisation of claudin-4 and other sealing tight junction proteins back into proper junctional positions following barrier insult. The barrier is restored, not just held in place.

Local action, minimal systemic absorption: Larazotide's oral bioavailability is deliberately low — it's designed to act in the gut lumen on luminal-facing receptors, not enter circulation. This is why side effects are minimal: there's almost no systemic exposure.

Brush-border degradation: Larazotide is degraded by aminopeptidase M on the intestinal brush border, producing peptide fragments. Some of these fragments retain partial activity, which extends the effective duration beyond the parent compound's residence time.

The mechanism is structurally distinct from BPC-157 (which works through growth factor receptor mechanisms in connective tissue and gut), from butyrate (which feeds colonic epithelium metabolically), and from glutamine (which fuels small-intestinal enterocytes). Larazotide is the only compound in this space that acts at the specific receptor regulating tight junction state — not downstream of it, not upstream, but at the regulatory checkpoint itself.

Things to know

Safety & considerations

Mild

Headache — most-reported event across Phase 1 healthy-volunteer studies. Typically mild, transient, no dose-relationship established. Did not cause withdrawal in any participants.

Mild

Gastrointestinal discomfort — occasionally reported (nausea, mild abdominal discomfort, change in bowel pattern). Lower rate than placebo in some celiac trials. Likely not dose-limiting at any tested dose up to 36mg.

Unknown

Long-term safety beyond 6 months — most trial data covers 6–12 week treatment periods. The longest controlled exposure in published trials is ~6 months. Open-label extension data extends further but is less rigorous. Long-term continuous use beyond a year has not been formally studied.

Unknown

Use during pregnancy and lactation — not studied. Avoid. The same conservative position applies as for any peptide compound without specific pregnancy safety data.

⚠ Key Considerations

Larazotide is not approved by the MHRA, FDA, or any other regulatory agency for any indication as of May 2026. The Phase 3 program for non-responsive celiac was discontinued in 2022. Phase 2 trials continue in other indications.

Available through research-peptide vendors. Sourcing quality varies significantly — third-party testing (HPLC purity + mass spec identity) is the meaningful quality signal, not vendor marketing claims.

For celiac specifically: not a substitute for a gluten-free diet. The clinical trials all studied larazotide as an adjunct, not a replacement.

Timing matters. The pharmacology dictates pre-meal dosing — taken with or after the trigger meal, the barrier insult has already begun. Consistent pre-meal timing is the main protocol discipline.