TB-500 and Thymosin Beta-4: How It Works and What Studies Show

TB-500 is mostly talked about in sport and horse racing, where anti-doping labs look for it in urine samples. The story behind the name is more interesting, though. TB-500 is derived from thymosin beta-4, a protein found in almost every cell of the human body that governs how cells move.

In this article, we explain what thymosin beta-4 does in the body, why the name TB-500 doesn't always refer to the same molecule, what animal and human studies have shown, and what its regulatory status is.

What Is Thymosin Beta-4?

Thymosin beta-4 (Tβ4 for short) is a small protein made of 43 amino acids, with a molecular weight of roughly 4,960 daltons. It was discovered in the 1960s and 1970s by Allan Goldstein's group, which was studying substances from the thymus gland (hence the name). The team published its complete sequence in 1981.

Over time it became clear that the name is a little misleading. Tβ4 is not a thymic hormone. It is found in almost all cells and body fluids except red blood cells. Platelets contain a lot of it, and it is also present in the fluid that forms in a wound.

A 1991 study clarified its main job. Tβ4 is the main actin-binding protein inside cells. Actin forms the filaments of the cell's skeleton, which let the cell keep its shape and move. Tβ4 keeps a reserve of free actin molecules on standby, so when a cell needs to push out a protrusion and move, the building material is right at hand.

TB-500: The Whole Protein or Just a Piece?

This is where you need to pay attention. "TB-500" is not a scientific name but a trade name, and it is used for two different substances:

• synthetic thymosin beta-4, i.e. the whole 43-amino-acid protein,
• a short fragment of seven amino acids (Ac-LKKTETQ). This is the actin-binding stretch of Tβ4 at positions 17–23.

In the anti-doping literature, TB-500 means the short fragment. A 2012 study from the Hong Kong Jockey Club's racing laboratory describes it as "a synthetic version of an active region of thymosin β4". Sellers, however, often use the same name for the whole protein.

For research, the difference is fundamental. Most of the studies described below worked with the whole protein. Mass spectrometry in the certificate of analysis shows what is in a given vial: a mass of around 4,960 Da means the whole protein, around 890 Da the fragment. We explain how to read a certificate in our article Peptide Certificate of Analysis.

How Thymosin Beta-4 Works

Unlike hormones, Tβ4 doesn't act through a single receptor. Research has described several pathways that complement one another:

• Cell movement. By binding actin, it lets cells rebuild themselves quickly and travel to where they are needed. In wound healing, these are mainly skin and blood-vessel cells.
• Blood vessel formation (angiogenesis). In 2003, researchers found that new vessel formation is triggered by the LKKTETQ stretch itself. That is why it became a separate fragment.
• Cell survival. In heart cells, Tβ4 activates the enzyme ILK (integrin-linked kinase) and, through it, the Akt pathway, which protects cells from dying.
• Dampening inflammation and scarring. The body cleaves the tetrapeptide Ac-SDKP from Tβ4. In studies, it slowed tissue fibrosis.

A 2005 review summed it up neatly in its title: a protein whose main job is to bind actin "moonlights" by repairing injured tissues.

What Animal Studies Have Shown

Wound Healing

The key study appeared in 1999 in the Journal of Investigative Dermatology. Researchers at the US National Institutes of Health (NIH) studied full-thickness skin wounds in rats. Tβ4 applied to the wound or given into the abdominal cavity sped up healing:

• new skin covered the wound 42% faster than in controls on day 4 and up to 61% faster on day 7,
• by day 7 the wounds had contracted at least 11% more,
• the wounds contained more collagen and more new blood vessels.

In a lab test, Tβ4 also sped up the movement of skin cells, even in very small amounts.

The Heart

In 2004, Nature published a study from the University of Texas. Researchers tied off a coronary artery in mice to cause a heart attack. In mice given Tβ4, more heart cells survived and the heart worked better afterwards. The authors also described the mechanism via the enzymes ILK and Akt.

Three years later, another Nature paper came out of London. It found that in the adult heart, Tβ4 wakes up progenitor cells in the heart's outer layer (the epicardium), which then form new blood vessels. These two studies made Tβ4 a talked-about candidate for treatment after a heart attack.

The Brain After a Stroke

In 2010, a team from Henry Ford Hospital in Detroit studied Tβ4 in rats after a stroke. Animals that received it recovered better in tests of movement and coordination. Studies after brain injuries reported similar results.

Hair

A lesser-known 2004 study found that Tβ4 sped up fur growth in rodents. It activated hair follicle stem cells and helped them move to the spot where a new hair forms.

Human Studies

Unlike BPC-157, thymosin beta-4 has gone through a number of clinical trials. They were run by the US company RegeneRx, which developed three products: an injectable, a skin gel and eye drops. All of the trials studied the whole protein, not the fragment.

• Safety (phase 1, 2010). Forty healthy volunteers received Tβ4 intravenously, once and daily for 14 days. Adverse events were infrequent and mild, with no serious ones. The study was meant to pave the way for research in heart attack patients.
• Venous leg ulcers (phase 2, 2010). A study at eight European sites enrolled 73 patients. The Tβ4 gel was as safe as placebo. At one concentration, the authors saw a hint of faster healing, but the study did not provide clear proof.
• Dry eye (phase 2, 2015). The study enrolled 72 people. Neither of the two primary endpoints was met. Several secondary measures did improve, however; for example, discomfort in a challenge test fell by 27%. No adverse events were observed.

Development continued in larger trials, mainly for eye conditions. However, no thymosin beta-4 product has been approved to date. There are no published clinical trials of the short TB-500 fragment.

Safety: What We Know and What We Don't

Human studies of the whole protein have not found serious problems so far, but they were small and short. Several questions remain open:

• Tumours. Tβ4 helps cells move and supports blood vessel formation. Tumours exploit both. A 2004 study linked higher activity of the Tβ4 gene to colon cancer cells invading surrounding tissue more readily, and to metastasis in patients. This doesn't mean Tβ4 causes cancer. It is, however, a reason why long-term effects need dedicated research.
• The fragment is not the whole protein. Results from Tβ4 studies cannot automatically be applied to the seven-amino-acid fragment. It has only some of the functions, and there is almost no safety data on it.
• Long-term use. The longest human studies lasted weeks, not years.

TB-500 in Sport and Horse Racing

The World Anti-Doping Agency (WADA) explicitly lists "thymosin-β4 and its derivatives, e.g. TB-500" on its Prohibited List. They are banned at all times, in and out of competition.

The biggest case involved Australian football. In January 2016, the Court of Arbitration for Sport (CAS) found 34 current and former Essendon players guilty of using thymosin beta-4 during the club's 2012 supplements programme. All of them received two-year bans.

TB-500 is also tested for in horse racing. A method that detects it and its breakdown products in horse urine and blood was published in 2012 by the Hong Kong Jockey Club's racing laboratory.

Regulatory Status

Neither thymosin beta-4 nor TB-500 is approved as a medicine in the United States (FDA), the European Union (EMA) or the United Kingdom (MHRA). They are sold only as research compounds.

In the US, the situation has been shifting. In 2023, the FDA placed the thymosin beta-4 fragment among substances that pharmacies were not allowed to compound. In July 2026, however, an FDA advisory committee recommended adding TB-500, along with five other peptides, to the substances pharmacies may compound. You'll find the details in Peptide News 43/2026. A final decision has not yet been made. Nothing is changing in the EU regulation of these peptides.

TB-500 and BPC-157

Both peptides are studied in connection with tissue regeneration, which is why they are often mentioned together. They differ in origin and mechanism, though. BPC-157 is derived from a protein in gastric juice and acts more locally, mainly through nitric oxide and the VEGF pathway. Thymosin beta-4 is a protein found throughout the body, and its main role is binding actin and moving cells. The human evidence also differs widely: Tβ4 has been through clinical trials up to phase 3, while BPC-157 has only a few small studies. For a detailed comparison, see BPC-157 vs TB-500: Key Differences and What Studies Show.

Research Timeline

Frequently Asked Questions

Is TB-500 the same as thymosin beta-4?

Not always. The name TB-500 is used either for the whole thymosin beta-4 protein (43 amino acids) or for its short stretch Ac-LKKTETQ (7 amino acids). Mass spectrometry in the certificate of analysis shows which one it is.

What does thymosin beta-4 do in the body?

It binds actin, which makes up the filaments of the cell's skeleton. This lets cells rebuild themselves quickly and move. In studies, it also supported blood vessel formation and cell survival, and dampened inflammation.

Why is TB-500 studied alongside BPC-157?

Both are studied in connection with tissue regeneration, but each works differently. Thymosin beta-4 acts mainly through cell movement, BPC-157 through blood vessel formation and nitric oxide. That is why researchers often compare them.

Has thymosin beta-4 been tested in humans?

Yes. The whole protein has gone through phase 1 to 3 trials: as an injection in healthy volunteers, as a gel for venous leg ulcers and as eye drops for dry eye. It was well tolerated, but a convincing effect has not yet been shown. The short TB-500 fragment has not been tested in humans.

Is TB-500 banned in sport?

Yes. WADA lists thymosin beta-4 and its derivatives, including TB-500, among substances banned at all times. It is also banned in horse racing.

Is TB-500 an approved medicine?

No. It is not approved in the US, the EU or the UK. It is available only as a research compound.

What does "research use only" mean?

It means the substance is intended for laboratory and scientific research. It is not a medicine or a dietary supplement and is not intended for use in humans or animals.

Summary

Thymosin beta-4 is a protein that almost every cell contains and that allows it to move. In animal studies, it sped up wound healing, protected the heart after a heart attack and helped the brain after a stroke. In humans, it has gone through clinical trials that confirmed it is well tolerated, but not yet a convincing effect.

TB-500 is a trade name used either for the whole protein or for a short stretch of it. For research, it is therefore crucial to know exactly what is in the vial. The answer comes from a certificate of analysis with mass spectrometry.

You'll find an overview of TB-500 and other research peptides on our research compounds page: TB-500.

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