At a glance

What is thymosin beta-4?

Thymosin beta-4 is a small, naturally occurring 43-amino acid peptide found in most cells and body fluids, released at sites of injury by platelets and immune cells. It plays a role in cell movement and tissue repair. It is sold through wellness and "research peptide" channels for recovery and healing, and it is not an approved medicine. (A marketed fragment of this peptide, TB-500, is catalogued separately.)

How does it work?

Thymosin beta-4 binds a cell-structure protein called actin and promotes:

• Cell migration
• The mobilization of stem and progenitor cells
• New blood-vessel formation
• Reduced inflammation and scarring

This mechanism is well characterized in laboratory and animal models of wound, eye, heart, and nervous-system repair. This describes the proposed mechanism, separate from demonstrated benefit in people.

Is it FDA-approved?

No. Thymosin beta-4 is not approved by the FDA, and it is not available through Superpower. In sport, it is prohibited at all times under the growth-factor section of the WADA list. The 2026 FDA compounding advisory meetings reviewed its marketed fragment TB-500, not the full-length peptide.

What does the research show?

The animal and laboratory base is large, but human data are limited. According to PubMed, human experience is confined to small or early trials, such as a review of its regenerative properties¹ and a randomized dose-escalation venous-ulcer study² assessing safety and tolerability, plus eye-drop trials that reached Phase III in dry eye³. No pivotal trial has established efficacy for a general recovery or wellness use, so its marketed benefit is unproven in people. In the Phase III neurotrophic keratopathy trial⁴, the results were:

The difference (p = 0.0656) was a trend short of the usual significance cutoff.

Frequently asked questions

What is the difference between thymosin beta-4 and TB-500?

Thymosin beta-4 is the full endogenous 43-amino-acid peptide⁵ found in most mammalian cells. TB-500 is a synthetic 7-amino-acid acetylated fragment (Ac-LKKTETQ) corresponding to residues 17 through 23 of that sequence, which researchers describe as the active site for actin binding⁶ and cell migration. The clinical trial data, including the Phase II and Phase III ophthalmic trials and the 2025 cardiac RCT⁷, all involve full-length Tβ4. TB-500 has no comparable human trial program as of September 2026, and FDA has identified no human exposure data⁸ for it.

Is thymosin beta-4 FDA-approved?

No. As of September 2026, thymosin beta-4 is not FDA-approved for any indication. The RGN-259 ophthalmic program (0.1% Tβ4 eye drops developed by ReGenTree) has completed Phase III trials in dry eye³ and has a Phase III trial in neurotrophic keratopathy⁹ listed as recruiting, but no FDA marketing approval has been granted.

What are the side effects of thymosin beta-4?

The available human safety data from two Phase I studies, published in the Annals of the New York Academy of Sciences¹⁰ in 2010 by Ruff and colleagues and in the Journal of Cellular and Molecular Medicine¹¹ in 2021 by Wang and colleagues, reported Tβ4 as well tolerated in healthy volunteers across single and multiple doses up to 1,260 mg intravenously. In a Phase III eye-drop trial⁴ in neurotrophic keratopathy, no significant adverse effects were observed. Long-term safety data for chronic subcutaneous use are limited.

Can you get thymosin beta-4 without a prescription?

No. Thymosin beta-4 is not legally available over the counter in the United States. Products marketed online are unregulated and may not contain what they claim.

How does thymosin beta-4 work for wound healing?

In preclinical models, Tβ4 has been studied for its effects on wound healing primarily through two mechanisms: it sequesters G-actin monomers, which helps cells such as keratinocytes reorganize their cytoskeletons and migrate toward the wound edge; and it promotes angiogenesis, the new blood-vessel growth that supplies healing tissue. A proposed anti-inflammatory effect may also modulate the inflammatory environment that can slow repair. The foundational preclinical data from Malinda and colleagues in 1999 demonstrated a 42% increase in reepithelialization¹² at day 4 (up to 61% at day 7) in a rat full-thickness wound model. No large-scale human wound-healing RCTs have been completed as of September 2026.

Are peptides legal in 2026?

Legality depends on the specific compound, its regulatory status, and the context of use. Thymosin beta-4 is not FDA-approved and is not approved for OTC sale. As of September 2026, its fragment TB-500 is not eligible for 503A compounding: FDA removed it from Category 2⁸ in April 2026 after the nomination was withdrawn, but it is not on the 503A bulks list or in Category 1. For athletes, Tβ4 is prohibited under the 2026 WADA Prohibited List (Section S2). Consult a qualified provider or regulatory expert for guidance specific to your situation.

What changed on FDA's peptide compounding list in 2026?

FDA announced on April 15, 2026¹³ that its advisers would review compounding restrictions on 12 peptides, and by April 22 it had moved TB-500 off its Category 2 list⁸ after nominators withdrew their nominations. That was not a finding that the peptides are safe, and TB-500 (the thymosin beta-4 fragment) is not on the 503A bulks list or in Category 1. On July 23, 2026, an FDA advisory committee voted 8-6 to recommend TB-500¹⁴ for wound healing for the bulks list, a non-binding vote that still requires FDA rulemaking. Consult a qualified provider for guidance specific to your situation.

Is thymosin beta-4 prohibited in sport?

Yes. As of the 2026 WADA Prohibited List, thymosin beta-4 is classified as a prohibited substance under Section S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics). This prohibition applies both in competition and out of competition. TB-500 is equally prohibited under the same section. Athletes subject to anti-doping rules governed by WADA or their sport's governing body should not use thymosin beta-4 or TB-500, regardless of source, and should consult their sport's anti-doping authority before using any related peptide.

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