Is PN-943 FDA-approved, and what does the research show?

What is PN-943?

PN-943 is an investigational drug: a small peptide made to be swallowed and to act inside the gut ¹. A peptide is a short chain of amino acids, the building blocks of proteins. The paper on its first-in-human study calls it "a small disulfide-containing cyclic peptide" ¹. A first-in-human study is the first to give a drug to people. Cyclic means that the chain forms a ring, and a disulfide is a bond between two sulfur atoms.

Its target is the α4β7 integrin, said "alpha-4 beta-7." An integrin is a protein on a cell's surface. This one sits on certain white blood cells, called leukocytes, and is chiefly involved in recruiting them to the gut lining and its lymph tissue ¹. PN-943 "binds specifically to the α4β7 integrin on leukocytes," the paper's authors write ¹. They also call it gastrointestinal-restricted, meaning that it stays mostly in the gut and little of it enters the blood ¹.

The disease it has been studied for is ulcerative colitis ². The first-in-human paper describes that as "a chronic inflammatory bowel disease with a remitting and relapsing course, characterized by bloody diarrhea, abdominal cramps, and fatigue" ¹. Remitting and relapsing means that it eases and then flares again.

Protagonist Therapeutics sponsored the trial of PN-943 in patients and funded the first-in-human studies ², ¹. PN-943 is "a structural analog of PTG-100," an earlier peptide aimed at the same target, whose trial the same company sponsored ¹, ⁴. An analog is a close chemical relative.

PN-943 is not a weight-loss, wellness or performance product. The studies of it cited here enrolled healthy volunteers or adults with ulcerative colitis, and none measured weight loss as an outcome ¹, ².

Is PN-943 FDA-approved?

PN-943 is not FDA-approved: Drugs@FDA lists no approved PN-943 product as of November 9, 2026 ³. It is an investigational drug: ClinicalTrials.gov gives the status of its phase 2 trial in ulcerative colitis as "Completed," last update posted April 25, 2023 ². Investigational means still under study and not approved for sale. Drugs@FDA is FDA's public database of approved drug products, and ClinicalTrials.gov is the U.S. government's registry of clinical trials. Because no product is approved, PN-943 has no FDA-approved label, the document that sets out a drug's approved uses and warnings ³.

A phase 2 trial is a mid-stage study that tests a drug in people who have the disease. A ClinicalTrials.gov search for the intervention PN-943 on November 10, 2026 returned one study, that phase 2 trial ². The record gives a completion date of February 16, 2023, and no results had been posted to it at that reading ². Protagonist's annual report for 2024 says it completed the phase 2 trial in early 2023 and does not intend to dedicate further internal resources to PN-943's clinical development ⁵.

No source cited here shows a way to obtain PN-943 outside a clinical trial, and that one trial is "Completed" ². Compounding is the making of a medicine by a pharmacy for an individual patient. FDA's list of bulk substances nominated for compounding under section 503A of the drug law, updated May 14, 2026, does not name PN-943 ⁶. FDA's separate 503B list, for the compounders it calls outsourcing facilities, updated March 21, 2025, does not name it either ⁷. The phase 2 trial's registry record lists no expanded access program ².

See the FDA status of every peptide, updated weekly.

How does PN-943 work?

PN-943 is an antagonist of α4β7, meaning that it binds to the protein and blocks it ¹. The protein's main partner is a molecule called MAdCAM, which is found on the lining of the gut's blood vessels and in larger amounts in inflamed tissue ¹.

The proposed mechanism follows from that. By blocking the movement of white blood cells into the gut and their activation there, PN-943 "may inhibit colon inflammation," the authors write ¹.

Studied in people: in healthy volunteers, PN-943 reached its target on blood cells ¹. The measure was receptor occupancy, the share of α4β7 on a type of T cell in the blood that the drug had bound ¹. A T cell is a kind of white blood cell. After a single dose, mean peak occupancy rose from 61.8% at the lowest dose to 94.8% at the highest, against 8.6% with placebo ¹. The amount of α4β7 on those cells also fell as the dose rose ¹.

Very little of the drug entered the blood. Plasma concentrations were more than 6,000 times lower than concentrations in stool, and less than 0.1% of a dose left the body intact in urine ¹.

The same paper names another drug with the same target: vedolizumab, an antibody against α4β7 that is given into a vein ¹. The authors write that it "has been approved for the treatment of moderate to severe ulcerative colitis and Crohn disease in adult patients who are not responding to ≥1 conventional treatments" ¹. Crohn disease is another inflammatory bowel disease, and "≥1" means at least one. The paper does not name the regulator that approved it ¹. PN-943 is a different kind of molecule, taken by mouth, and no study cited here compares the two ¹.

What does the research show?

Studied in people: the registry record describes a randomized, double-blind, placebo-controlled phase 2 trial in 169 adults with moderate to severe active ulcerative colitis ². Randomized means assigned to a group by chance. Placebo-controlled means compared with a dummy treatment, and double-blind means that neither participants nor investigators knew who received which.

Participants were 18 to 75 years old ². Each had responded poorly to, stopped responding to or could not tolerate at least one standard treatment that the record lists ². The record lists four kinds of medicine: aminosalicylates, corticosteroids, immunomodulators and biologic drugs ². The first two reduce inflammation, immunomodulators damp the immune system, and biologic drugs are medicines made from living cells. Anyone previously treated with vedolizumab was excluded ².

They were assigned in equal proportions to a higher dose of PN-943, a lower dose or a matching placebo, each taken by mouth twice a day for 12 weeks ². Those who completed that period could be eligible for a further 40 weeks of treatment ². The record gives a start date of August 5, 2020 ².

The primary outcome the trial set out to measure, in the registry's words: "Proportion of subjects achieving clinical remission at Week 12 compared to placebo" ². Remission was to be judged with the Adapted Mayo score, the sum of three subscores: stool frequency, rectal bleeding and endoscopic findings ². Endoscopy is an examination of the bowel with a camera. Secondary outcomes compared the high dose and the low dose individually with placebo on endoscopic and tissue measures ².

The registry record carried no posted results when it was read on November 10, 2026, and the paper on PN-943 cited here was published before the record's completion date ², ¹. Protagonist's April 2022 release reports clinical remission in 27.5 percent on the lower dose against 14.5 percent on placebo in its modified intent-to-treat analysis (p = 0.08) ⁸. The higher dose did not meet the primary endpoint ⁸. The release says "159 patients" were randomized ⁸; the registry record describes a trial in 169 adults ².

Studied in people: a first-in-human study, 97 healthy men, safety, drug levels and target binding ¹. Forty took single doses and 57 took repeated doses, of PN-943 or placebo ¹. In the dose-escalation cohorts, groups that each took a higher dose than the last, eight men received PN-943 for every two on placebo, assigned at random and double-blind ¹. A second study enrolled 10 healthy men and women to compare a tablet with a liquid form, each taken in turn ¹. Both ran at one clinical center in Melbourne, Australia ¹.

These studies measured safety, how much drug reached the blood and how fully it bound its target; neither measured an effect on ulcerative colitis ¹. Blood levels rose roughly in step with the dose ¹. In the first study, a high-fat meal before the dose lowered them ¹. Twice-daily dosing held target binding steadier than once-daily dosing of the same daily total ¹.

The longest course in these studies was 14 days ¹. The authors concluded that the findings supported "further investigation in efficacy studies" ¹. All seven authors were employees and stockholders of Protagonist Therapeutics ¹.

Studied in animals: the same paper summarizes earlier work in rats with chemically induced colitis ¹. In those rats, PN-943 produced "a significantly lower mean colon histopathology score compared to rats treated with vehicle or PTG-100" ¹. A histopathology score grades tissue damage under the microscope, and vehicle is the inactive liquid without the drug.

PTG-100, the earlier peptide, was tested in a separate trial with its own registry record, and nothing in that record is a result for PN-943 ¹, ⁴. The record describes a randomized, double-blind, placebo-controlled phase 2 trial of PTG-100 in 98 adults with moderate to severe active ulcerative colitis ⁴. Participants took PTG-100 or placebo once a day for 12 weeks ⁹, ⁴. The registry gives the PTG-100 trial's status as "Terminated," last update posted August 21, 2025, and the reason: "Data Monitoring Committee discontinued the trial due to futility-based outcome" ⁴. A data monitoring committee is an independent group that reviews a trial's results while it runs, and futility means that the interim results made a positive finding unlikely.

Protagonist's April 2022 release reports clinical remission in 27.5 percent on the lower dose against 14.5 percent on placebo in its modified intent-to-treat analysis (p = 0.08) ⁸. The higher dose did not meet the primary endpoint ⁸. None of the sources cited here reports a trial comparing it with an approved treatment, or studies it for weight, wellness or athletic performance.

What are the side effects?

The safety results cited here come from healthy volunteers who took PN-943 for 14 days at most, not from patients ¹. In the single-dose part of the first-in-human study, 14 of 40 men reported 23 adverse events ¹. An adverse event is any health problem recorded during a study, whether or not the drug caused it. Twelve of the 32 men given PN-943 reported 21 events, and two of the eight given placebo reported two ¹, Supplemental Table 2. Investigators judged seven of the 21 events after PN-943 related to treatment, and both events after placebo ¹.

All were mild or moderate except one severe headache at the lowest dose, judged unrelated to treatment ¹. Events reported by two or more men given PN-943 were nausea, upper respiratory tract infections, headache, presyncope (feeling faint) and somnolence (sleepiness); one man on placebo had a headache ¹.

In the repeated-dose part, which enrolled 57 men, 30 men taking PN-943 reported 68 adverse events, all but two of them mild ¹. Four men on placebo reported six mild events, mostly in the gut ¹. In the repeated-dose part, 49 of the 57 men took PN-943 and eight took placebo ¹.

Of the two events after PN-943 that were not mild, one was an upper respiratory tract infection rated moderate ¹. The other was a case of influenza after the man had left the clinic, rated severe and counted as a serious adverse event ¹. That is the formal category for events such as those that threaten life or need hospital care.

Events reported by two or more men on repeated doses were abdominal discomfort, flatulence, upper respiratory tract infection, back pain, dizziness and headache, the most common ¹. Those events were counted among men on PN-943; two on placebo reported flatulence ¹. No participant in that study was withdrawn because of an adverse event ¹. In the second study, one of 10 participants left after tonsillitis that was judged unrelated to the drug ¹. The authors reported no clinically relevant changes in vital signs, laboratory tests or heart tracings in the first study ¹.

The record of the phase 2 trial carried no posted adverse-event data on November 10, 2026 ². Protagonist's release says only that safety on the lower dose was similar to placebo, and gives no counts ⁸. The trial's entry rules excluded people who were pregnant or breastfeeding, and people with a chronic recurrent or serious infection, a known immunodeficiency or a history of major neurological disorders ². Those are one trial's entry rules, not warnings established for the drug. FDA has approved no label for PN-943, so there are no FDA warnings to quote ³.

In sport

PN-943 is not named on the 2026 Prohibited List of WADA, the World Anti-Doping Agency ¹⁰. Section S0 of the list covers non-approved substances: "Any pharmacological substance which is not addressed by any of the subsequent sections of the List and with no current approval by any governmental regulatory health authority for human therapeutic use (e.g. drugs under pre-clinical or clinical development or discontinued, designer drugs, substances approved only for veterinary use) is prohibited at all times" ¹⁰. FDA's records were the only regulator's records read here, and Drugs@FDA lists no approved PN-943 product ³. Whether that clause covers PN-943 is for anti-doping authorities to decide, and no conclusion is offered here.

What JumpstartMD offers

JumpstartMD does not prescribe PN-943. 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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