Sosne G, Qiu P, Goldstein AL, et al. (2010). Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J, 24(7):2144-51.
ReviewPMID 20179146DOI↩
What is TB-500?
Your body makes a small protein called thymosin beta-4. It’s found in almost every cell [1], and it’s especially plentiful in platelets, the blood cells that gather at a wound [2]. Its main job is managing actin, the protein scaffolding that lets cells change shape and move. That makes it a natural player in healing [3].
TB-500 is a lab-made copy of a tiny piece of thymosin beta-4: just 7 of its 43 amino acids (LKKTETQ), with a small chemical cap added to one end [S1]. Scientists focused on this piece because it’s the part of the protein that grabs actin. It also appears to drive cell movement, new blood vessel growth, and wound healing [1, 4]. Researchers first made this piece in the lab in 2003 [5]. A product called TB-500 followed around 2011, marketed to boost performance in racehorses and greyhounds [S1].
How might it work?
Thymosin beta-4 is a bit like a multi-tool: different parts of the protein seem to do different jobs [1].
- Helping cells move. The piece copied in TB-500 binds actin, which helps repair cells travel into an injury [1].
- Growing new blood vessels. In lab tests, this 7–amino acid piece turned out to be essential for thymosin beta-4’s ability to grow blood vessels, and on its own it worked about as well as the whole protein [5].
- Calming inflammation and scarring. These effects are mostly linked to a different part of the protein, a short piece called Ac-SDKP. TB-500 doesn’t contain it [1].
There’s an interesting twist. The body quickly breaks TB-500 down into even smaller pieces. A 2024 study found that TB-500 itself didn’t speed wound closure in lab-grown connective tissue cells, but one of its breakdown products did. The researchers suggested the breakdown product may be what actually does the work [6].
What has research found?
Most of these studies were done in animals, and most used the full thymosin beta-4 protein. Studies that tested TB-500 or its 7–amino acid piece are labeled.
Skin wounds
In rats, thymosin beta-4 applied to the skin or injected boosted the regrowth of skin over a wound by 42% after 4 days and up to 61% after 7 days, with more collagen and new blood vessels [7]. It also helped wounds heal in diabetic and elderly mice, where healing is normally slow. The 7–amino acid piece worked about as well as the full protein in the older mice [8].
Heart
After a heart attack in mice, thymosin beta-4 helped heart muscle cells survive and improved heart function [9]. In lab experiments, it also reawakened resting cells from the heart’s outer layer, which then developed into the cells that build blood vessels [10].
Tendons
TB-500: In a 2026 rat study, rats given TB-500 after Achilles tendon repair had stronger tendons and better-organized tissue after four weeks than untreated rats. Combining TB-500 with BPC-157 didn’t add any extra benefit [11].
Eyes
Thymosin beta-4 eye drops have been tested in people (see below). TB-500: In 2025, researchers built a gel containing the LKKTETQ piece that sped healing of chemical burns on the cornea in a lab injury model [12].
Brain
In rats, thymosin beta-4 improved recovery after a stroke [13]. TB-500: In mice bred to develop an Alzheimer’s-like disease, TB-500 reduced brain inflammation and improved performance on memory tests [14].
Hair
A fun one: thymosin beta-4 sped up hair growth in rats and mice by activating stem cells in hair follicles [15].
What about studies in people?
TB-500 itself has never been tested in people. FDA reviewers found no published study in which TB-500 was given to humans for any reason [S1].
The full thymosin beta-4 protein, on the other hand, has been through several clinical trials:
- Safety studies: In healthy volunteers, thymosin beta-4 given by IV, even at high doses daily for two weeks, was well tolerated with no serious side effects [16, 17].
- Skin ulcers: In a trial of 73 people with leg ulcers caused by poor circulation, a thymosin beta-4 gel was as safe as a placebo (a dummy treatment) and showed signs of faster healing [18]. Across trials in leg ulcers and pressure sores, patients whose wounds healed did so almost a month faster [19].
- Dry eye: In a small trial of 9 people, thymosin beta-4 eye drops significantly reduced eye discomfort and damage to the eye’s surface compared with placebo drops [20].
- Slow-healing corneal damage: In a larger, late-stage trial of 18 people with neurotrophic keratopathy, a condition where the cornea loses nerve supply and struggles to heal, 6 of 10 treated patients healed completely within four weeks, compared with 1 of 8 on placebo. The main result fell just short of statistical significance, but comfort improved and no significant side effects were seen [21].
These results are genuinely encouraging for thymosin beta-4. But they used the full protein, made to pharmaceutical standards and given as eye drops, gels, or IV infusions under medical supervision. That’s very different from injecting TB-500 bought online.
How strong is the evidence?
| What we know so far | What we still don’t know |
|---|---|
| Thymosin beta-4 has helped healing in skin, heart, eye, and brain studies in animals [22] | Whether TB-500 alone does the same; research on TB-500 itself is thin [6] |
| The full protein has reached later-stage human trials with a good safety record [16, 21] | Anything about TB-500 in people, because no human studies exist [S1] |
| The TB-500 piece matched the full protein in lab tests of blood vessel growth [5] | Whether TB-500 is safe, because no toxicity studies have been published [S1] |
| A 2026 rat study found TB-500 improved tendon healing [11] | The right dose, how often, or for how long [23] |
A few more things to keep in mind:
- Results for the full protein don’t transfer automatically. TB-500 contains only one of thymosin beta-4’s active regions [1].
- Some key trials were designed by the companies developing the treatment. For example, the company developing the eye drops designed the late-stage eye trial, although an independent research organization ran it [21].
- There’s no human data on injuries yet. A 2026 sports medicine review noted that human data on muscle, tendon, and bone injuries are lacking for both thymosin beta-4 and TB-500 [23].
Safety: what we know
- The full protein looks well tolerated in trials. Safety studies and later-stage trials of thymosin beta-4 haven’t found serious side effects [16, 17, 18, 21].
- TB-500 hasn’t been safety-tested. FDA found no toxicity studies and no human data, and called the lack of human safety information a particular concern [S1].
- Products may not contain what they claim. When a French horse-racing laboratory tested products sold online as TB500 and TB1000, their contents didn’t consistently match their descriptions [24]. FDA has also noted that impurities and clumping in injected peptides could trigger immune reactions [S1].
- The cancer question. Thymosin beta-4 helps cells move and grow blood vessels, which are also things tumors rely on to spread. In mice, cancer cells engineered to make extra thymosin beta-4 formed bigger tumors and spread more to the lungs [25]. Higher levels have also been found in several kinds of tumors that spread [26]. Nobody knows yet whether taking TB-500 affects cancer risk, but experts flag it as an important open question [27].
Legal status
- Not an approved medicine anywhere. It isn’t part of any FDA-approved drug [S1], and products sold online lack approval from US or European regulators [24].
- United States: FDA’s reviewers recommended against letting pharmacies prepare (compound) TB-500, citing the lack of human data. An FDA advisory panel voted in favor in July 2026, and a final decision is still pending [S1, S2].
- UK: UK law doesn’t allow unauthorized medicines to be sold [S3].
- Sports: Thymosin beta-4 and TB-500 have been named on the World Anti-Doping Agency (WADA) banned list since 2018 [S1, S4]. Tests exist to detect TB-500 in both human and horse sports [4, 28].
The bottom line
Thymosin beta-4 is one of the more promising natural repair proteins scientists have studied. It has helped healing in animals, from skin to heart to brain, and it has reached human trials for eye and skin conditions with a good safety record so far.
TB-500 is a different story. It’s a small piece of that protein, and its own research is just getting started: a handful of animal and lab studies, no human data, and an open question about whether the fragment itself or its breakdown products do the work. If the next wave of studies tests TB-500 directly, we’ll finally learn whether this small piece can live up to the promise of the full protein.