TB-500 (Ac-LKKTETQ, thymosin beta-4 fragment 17-23)
TB-500: What The Studies Actually Say
No study has ever given TB-500 to a person. Its results come from rats, horses and lab dishes, and the human trials people point to used a different, bigger molecule. Here is what the research actually found.
Updated 22 September 2026
Before you read this
This page explains what published studies found. That is all it is. It is not medical advice, and it is not instructions for using anything. Nothing here is meant to find, treat, cure or stop any illness. The compounds discussed on this site, retatrutide included, are not approved by the FDA for use in people. Research compounds are sold for laboratory use only — not for use in humans or animals. A study tells you what happened to the people in it. It does not tell you what would happen to you. What you do with what you read here is your responsibility, so talk to a doctor first. This page is published by Ascend Vials, which sells research compounds.
Read the full guide
Confirm you have read the notice above and enter an email address. We will send you a link back to this guide, and sometimes an email when we publish a new one. You can unsubscribe any time.
You have probably heard that TB-500 helps injuries heal. FDA looked for a single study of it in a person. It found none.
Here is what the research actually found. Every claim has a link. Read them yourself.
The 30-second version
- TB-500 is a lab-made piece of a natural protein: 7 amino acids copied from thymosin beta-4, which is 43 long. Sellers often mix up the two names. They are not the same thing.
- No study has ever given TB-500 to a person. FDA found no human data at all.
- The human trials people point to used the whole protein. In the biggest of them, it showed no clear win over placebo.
- The TB-500 results come from rats, horses and lab dishes. The most positive: stronger repaired rat tendons, with 4 rats per group tested.
- In one lab test, TB-500 itself did not speed wound healing. One of its broken-down pieces did.
- It is not approved in the US, Europe, Canada, Australia or the UK, and it is banned in sport. A July 2026 FDA advisory vote is only advice.
- Nothing sold online has been shown to match what the studies used. No study has checked.
What it is
TB-500 is a lab-made peptide seven amino acids long, written Ac-LKKTETQ. It copies positions 17 to 23 of a natural protein called thymosin beta-4, with a small chemical tag, an acetyl group, added to the front. FDA review, 2026
It started in animal racing. According to FDA, a veterinary TB-500 product appeared in 2011 and was marketed to boost performance in racehorses and greyhounds. FDA review, 2026 When anti-doping labs took TB-500 products apart, the seven-piece fragment was the key ingredient. Drug Test Anal, 2012 · J Chromatogr A, 2012
"TB-500" is a nickname, not an official drug name. FDA has seen several salts and variants, including different active molecules, sold under that one name. FDA review, 2026
Two different things share one name
Thymosin beta-4 is a natural protein found in nearly every cell. Its main job is holding actin, the building blocks of a cell's inner skeleton, in reserve. Sosne, 2010 TB-500 is one small piece of it. FDA says websites often treat the two as the same thing. They are not. FDA review, 2026
| TB-500 | Thymosin beta-4 | |
|---|---|---|
| Size | 7 amino acids | 43 amino acids |
| Made by the body? | No | Yes, in nearly every cell |
| Given to people in a study? | Never | Yes: eye drops, skin gel, into a vein |
| Has the piece linked to less scarring? | No | Yes |
| FDA approved | No | No |
Sources: FDA review, 2026 · Sosne, 2010 · openFDA search for "thymosin" — no matches
Not one study in a person
FDA's 2026 review searched the big medical databases, the US trial registry and its own side-effect reports. It found no study, no case report and no blood measurement of TB-500 in any person. In FDA's words, its potential safety risks in humans "are unknown." FDA review, 2026
A rat or horse result tells scientists what to test next in people. It does not tell you what happens in a person.
The human trials used the whole protein
If you have read that "TB-500" was tested on wounds, eyes or hearts, those trials used the whole thymosin beta-4 protein. None used TB-500.
| Study | Form | People | Main result |
|---|---|---|---|
| Leg ulcers | Skin gel | 72 | Healed: 22%, against 24% on placebo |
| Pressure sores | Skin gel | 72 | Healed: 15%, against 17% on placebo |
| Blistering skin disease | Skin gel | 30 | No benefit shown. Stopped early |
| Severe dry eye | Eye drops | 9 | Less discomfort and surface damage than dummy drops |
| Dry eye | Eye drops | 72 | Missed both main goals |
| Dry eye, ARISE-2 | Eye drops | 601 | No clear difference from placebo |
| Dry eye, ARISE-3 | Eye drops | 699 | About the same as placebo |
| Nerve-damaged cornea | Eye drops | 18 | 6 of 10 healed, against 1 of 8. Not statistically significant |
| Heart attack, China | Lab-grown protein | 96 | No difference overall |
Read the size column. The only clear win had 9 people. The two biggest trials, with hundreds of people each, showed no clear difference from placebo. Those were late-stage trials, the kind that decide whether a drug gets approved.
To be fair: a later review says ulcer patients who did heal got there almost a month sooner. Treadwell, 2012 In the heart trial, damage was smaller only in a subgroup: 43 patients first treated within 8 hours of having the artery reopened. Cardiovasc Res, 2025 A 2025 Cochrane review rated the cornea result low-certainty. Cochrane, 2025
Employees of the companies developing the protein co-wrote the cornea and heart papers. Int J Mol Sci, 2022 · Cardiovasc Res, 2025
There is no human TB-500 number to chart, so there is no chart here.
What TB-500 itself was tested in: rats, horses and dishes
Rat tendons. In a 2026 study, rats had an Achilles tendon cut and stitched, then got daily TB-500, BPC-157, both, or nothing for about four weeks. The TB-500 tendons took more force to break: a median of 37.4 newtons, against 26.9 untreated. Adding BPC-157 added nothing. Jt Dis Relat Surg, 2026
The fine print: only 4 rats per group were strength-tested. The TB-500 came from a commercial seller, and the paper does not report its sequence or purity. Full text
Wounds in a dish. Skin-repair cells were scratched. Intact TB-500 closed the scratch no faster than a blank solution. One of its broken-down pieces, Ac-LKKTE, did speed it up, by a small amount. The authors suggest earlier healing claims may belong to that piece. J Chromatogr B, 2024
How fast it breaks down. Horses got one injection under the skin. Blood levels peaked within two hours at a few hundredths of a billionth of a gram per millilitre. By 6 to 10 hours, intact TB-500 could no longer be measured, and shorter pieces showed up in blood and urine. FDA review, 2026 · J Chromatogr A, 2012 Human serum, liver and kidney samples in the lab chopped it down the same way. J Proteomics, 2016
How it is supposed to work
TB-500's seven pieces sit on the protein's main actin-binding spot, a stretch linked to new blood vessels, wound healing and cells moving. A different piece, Ac-SDKP, is linked to less inflammation and scarring. TB-500 does not contain it. Sosne, 2010
In a dish, a lab-made copy of that seven-piece stretch worked about as well as the whole protein at making blood-vessel cells move and new vessels sprout. The summary does not say whether it had TB-500's tag. FASEB J, 2003 In old mice, the untagged stretch helped skin wounds close about as well as the whole protein. Wound Repair Regen, 2003 FDA warns the tag can change how a peptide binds and how long it lasts, so untagged results do not transfer straight to TB-500. FDA review, 2026
Older animal studies of the whole protein found faster-healing skin wounds in rats and better heart function in mice after a heart attack. J Invest Dermatol, 1999 · Nature, 2004
Side effects: nobody has counted
FDA's 2026 review found no TB-500 studies on harm from one dose or repeated doses, damage to genes, effects on fertility or unborn babies, or cancer. FDA review, 2026
The immune worry. FDA says injected TB-500 "may pose a significant risk for immunogenicity," the immune system treating it as an invader. Reactions can range from antibodies with no symptoms to "life-threatening and catastrophic reactions." FDA review, 2026
No reports is not the same as safe. FDA's side-effect database had no TB-500 reports through March 2025. FDA says reporting is voluntary and incomplete, so it cannot draw firm conclusions from that. FDA review, 2026
The cancer worry comes from the whole protein. Mouse skin-cancer cells built to make extra thymosin beta-4 seeded 46.7 tumor spots in the lungs on average, against 10.9 for normal cells. J Natl Cancer Inst, 2003 That was the protein made inside cancer cells, not an injected peptide. Nobody has tested TB-500 for this. FDA review, 2026
The whole-protein trials. In a safety study of 40 healthy volunteers, some on placebo, the protein given into a vein for up to 14 days caused few side effects, all mild or moderate. Ann N Y Acad Sci, 2010 A lab-grown version in healthy adults in China showed the same. J Cell Mol Med, 2021 In the pressure-sore trial, 13 of 54 people on the gel had a serious adverse event, against 5 of 18 on placebo. The record does not say whether the gel caused them. Trial record
That is short-term data on a different molecule. It does not transfer to TB-500.
Is it approved?
No. TB-500 is not an FDA-approved drug or part of one. No TB-500 product is approved in the European Union, Canada, Australia, the UK or the other European countries FDA checked. FDA review, 2026 The whole protein is not FDA-approved either. A late-stage trial of its eye drops was still listed as recruiting. openFDA search · Trial record
The compounding story, in order:
- FDA's list of compounding ingredients that "may present significant safety risks" has TB-500 as "nominated but withdrawn." FDA, 2026
- FDA's staff recommended against adding it to the list of ingredients pharmacies may use. FDA review, 2026
- On July 23, 2026, FDA's advisory committee met, and trade press reported a vote to recommend it. One outlet's 8-6 count covers three peptides together and does not add up to its own committee size. PharmExec, 2026 · NCPA, 2026
- The vote is only advice. In September 2026, FDA's meeting page showed no minutes, and TB-500 was not on the official list in federal regulations. FDA meeting page · eCFR
Australia. New South Wales lists TB-500 as a "prescribed restricted substance." NSW Health
Sport. The World Anti-Doping Agency bans "Thymosin-ß4 and its derivatives e.g. TB-500" at all times, in and out of competition. WADA, 2026
What is still unknown
- Whether TB-500 does anything in people, for anything.
- How the human body handles it, and what its broken-down pieces do.
- Whether the tag makes it act like the natural stretch, like the whole protein, or like neither.
- Whether repeated doses are safe. The standard safety tests have never been done.
- Whether the body makes antibodies against it.
- Cancer risk. Nobody has tested the fragment.
- Whether the rat tendon result holds up with more rats and checked material.
What is in the bottle is not what was studied
One more thing.
Every TB-500 result on this page came from a lab experiment. Rats. Horses. Cells in a dish. Every human result came from the whole protein, a different molecule.
And FDA found that "TB-500" is a loose label: FDA review, 2026
- Several variants are sold under the name, including different active molecules.
- Many websites treat TB-500 and the whole protein as the same thing.
- A public certificate of analysis for TB-500 checked only its look, identity and purity. It did not test strength, impurities, bacterial toxins or clumping.
No study has ever shown that a product sold online as "TB-500" is the same thing the studies used. Not the same purity. Not the same strength. Not even proof it is the same molecule.
So take every number on this page for what it is. It describes lab TB-500 in rats, horses and dishes, and a different protein in people. It describes nothing else.
How to check a number yourself
You are going to see more claims about TB-500. In a reel. In a comment. On somebody's store page.
Here is how to tell a real one from a marketing one. Five questions. About ten seconds each.
1. Is there a link to a study?
A real number comes from a paper you can open. No link means it is a claim, not a result. Search the name on pubmed.gov yourself. If nothing comes back, nothing was published.
2. Was it done in people?
For TB-500, so far the answer is always no. Look for "rats", "horses" or "cells" near the top of the paper. A rat result is a reason to run a human study. It is not a human result.
3. Was it TB-500, or the whole protein?
The big one here. If a paper says "thymosin beta-4", "Tβ4", "RGN-259" or "RGN-137", it tested the whole 43-amino-acid protein. That is a different molecule.
4. How many, and what was in the vial?
Small studies swing. The rat tendon result rests on 4 rats per group, using material whose sequence and purity were never reported.
5. Did it beat the group that got nothing?
That group is the whole point. In the leg-ulcer trial, 22% healed on the gel and 24% on the dummy gel. A headline can say "22% healed." It cannot honestly say the gel worked.
Now run those five on this page
Every number above links to its paper and says whether it came from rats, horses, dishes or the whole protein. The group sizes and placebo results are in the tables.
Whatever a seller claims TB-500 does in people, there is no human TB-500 study to link to, because none has been published.
That is the whole difference: a number you can check, and a number you are asked to believe.
This page has a date on it, near the top. If a human study of TB-500 is ever published, this page changes.
Read the studies yourself
- FDA review of TB-500, 2026 — the main one
- Rules: FDA safety-risk list · FDA meeting page · PharmExec · NCPA · eCFR · openFDA · WADA · NSW Health
- What TB-500 is: Esposito 2012 · Ho 2012 · Sosne 2010
- TB-500 in rats and dishes: Biçer 2026 (full text) · Rahaman 2024 · Zvereva 2016
- The seven-piece stretch: Philp, FASEB J 2003 · Philp, Wound Repair Regen 2003
- Whole protein, animals: Malinda 1999 · Bock-Marquette 2004 · Cha 2003
- Whole protein, skin: leg ulcers · pressure sores · blistering disease · Treadwell 2012
- Whole protein, eyes: Sosne, Cornea 2015 · Sosne, Clin Ophthalmol 2015 · ARISE-2 · ARISE-3 · Sosne 2022 · Cochrane 2025 · late-stage cornea trial
- Whole protein, veins and hearts: Ruff 2010 · Wang 2021 · Zhang 2025
Everything above about TB-500 describes lab and animal experiments. The human trials used the whole thymosin beta-4 protein, a different molecule. This is not advice, a plan, or instructions. TB-500 is not an approved medicine. Research compounds are not for human or animal use.