Is TB-500 FDA Approved? Parent in Phase 2 Trials

The Short Answer

TB-500 is not FDA-approved. But unlike many peptides in compounded use, its parent molecule Thymosin Beta-4 has actually been through human clinical trials. RegeneRx Biopharmaceuticals developed two clinical programs: RGN-137 (a topical gel for wound healing) and RGN-352 (an injectable for cardiac repair after heart attack). Both reached Phase 2.

The clinical trials showed positive safety profiles and preliminary efficacy signals. Development paused because of the company's funding constraints, not because of safety concerns or negative results. Thymosin Beta-4 is one of the most extensively studied peptides in the scientific literature, with work spanning wound healing, cardiac tissue biology, and inflammation. That research base is large, but almost all of it is preclinical, and the human trials never reached the size needed for FDA approval.

What Thymosin Beta-4 Actually Is

Thymosin Beta-4 (Tβ4) is a small 43-amino-acid peptide that your body already makes. It is one of the most abundant intracellular peptides in mammalian tissue, concentrated in platelets, white blood cells, and wound fluid. Its primary day-to-day job is holding a reserve pool of actin, the protein that builds the internal scaffolding of a cell. When a cell needs to change shape or crawl toward an injury, Tβ4 releases actin monomers on demand. That single function sits underneath most of the repair effects researchers have described.

Goldstein AL, "Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues," Trends in Molecular Medicine, 2005. View study

TB-500 is the compounded label for a synthetic copy of this molecule. Some suppliers use "TB-500" to mean a shorter active fragment rather than the full 43-amino-acid chain, so the name is looser than a drug name would be. When a licensed pharmacy compounds it, the intent is the full-length Tβ4 sequence.

Why It Is Not FDA-Approved

FDA approval requires a sponsor to run a molecule through Phase 1, Phase 2, and Phase 3 trials, then submit a New Drug Application for a specific indication and dose. Thymosin Beta-4 never completed that path. RegeneRx advanced two programs into Phase 2, but neither finished the large confirmatory trials the FDA needs, and no New Drug Application was ever approved. The gap is not a rejection on safety grounds. It is an unfinished development program that stalled for money.

This is the honest state of the evidence. There is a real human safety signal from early trials and a deep preclinical literature, but there is no completed Phase 3 trial, no approved indication, and no FDA-sanctioned dose for TB-500. A patient should read it as a promising but unproven compounded peptide, not as an approved medicine.

Clinical Trials: What Actually Happened

RGN-137: Wound Healing (Topical)

RegeneRx developed a topical gel formulation of Thymosin Beta-4 and studied it in patients with chronic and acute wounds, including venous stasis ulcers and epidermolysis bullosa (a rare genetic skin condition). The topical program reached Phase 2 and reported an acceptable safety profile with no systemic absorption concerns. Efficacy signals were preliminary and were never confirmed in a larger Phase 3 trial.

RGN-352: Cardiac Repair (Injectable)

The injectable program studied cardiac tissue repair after a heart attack. The rationale rested on Tβ4 biology: it promotes new blood vessel growth, cell migration, and a calmer inflammatory response, all relevant to recovering heart tissue. RGN-352 reached Phase 1/2, where the injectable was reported as safe and well tolerated. As with the topical program, the efficacy work did not progress to a completed confirmatory trial. Much of the supporting cardiac data is preclinical, including a porcine (pig) model of myocardial infarction.

Tan SH et al., "Thymosin β4 increases cardiac cell proliferation, cell engraftment, and the reparative potency of human induced-pluripotent stem cell-derived cardiomyocytes in a porcine model of acute myocardial infarction," Theranostics, 2021. View study

Why TB-500 Matters for Recovery

TB-500's value in recovery comes from its unique mechanism: it reorganizes the actin cytoskeleton inside cells, enabling them to migrate to injury sites. It also stimulates angiogenesis (new blood vessel formation), reduces inflammatory cytokines, and promotes organized collagen deposition over fibrotic scarring. This combination of cell migration, blood supply, and anti-inflammation is why practitioners use it for musculoskeletal recovery.

Goldstein AL et al., "Advances in the basic and clinical applications of thymosin beta-4," Expert Opinion on Biological Therapy, 2015. View study

Sosne G et al., "Biological activities of thymosin beta4 defined by active sites in short peptide sequences," FASEB Journal, 2010. View study

One of the clearer preclinical demonstrations comes from the eye. In an animal (in vivo) corneal injury model, topical thymosin beta-4 sped up corneal wound closure and dialed down inflammatory mediators at the injury site. That study is worth naming precisely because it shows the mechanism at work while also showing the limit of the evidence: it is an animal model, not a human recovery trial. Most of the musculoskeletal claims people cite for TB-500 rest on this kind of preclinical and mechanistic work rather than on controlled human data.

Sosne G et al., "Thymosin beta 4 promotes corneal wound healing and modulates inflammatory mediators in vivo," Experimental Eye Research, 2001. View study

Importantly, Thymosin Beta-4 is endogenous. Your body already produces it. It is present in nearly every cell and tissue, with high concentrations in wound fluid, blood platelets, and white blood cells. Compounded therapy adds more of a peptide the body already uses for repair, which is part of why its early safety profile looked clean, though endogenous does not automatically mean safe at supraphysiologic doses.

Current Regulatory Status

TB-500 is available as a compounded medication under federal pharmacy compounding law. It requires a prescription from a licensed provider and must be prepared by a licensed 503A or 503B pharmacy. PeRx does not sell TB-500 on its own. It is dispensed only inside the pre-mixed BPC/TB-500 combination vial, alongside BPC-157.

What FDA "Category 2" Means

When a 503A pharmacy wants to compound from a bulk substance that is not part of an FDA-approved drug, that substance has to be reviewed. The FDA sorts nominated bulk substances into two buckets. Category 1 substances may be used while the agency finishes evaluating them. Category 2 substances are flagged because the FDA has identified a potential significant safety risk or lacks enough data to clear them. Bulk thymosin beta-4 sits in Category 2. That is a gray zone: it is a caution flag and an unfinished review, not a ban, and it is why you will see TB-500 described as available but not endorsed.

Anti-Doping Status

Athletes need to know one more thing. Thymosin beta-4 is on the World Anti-Doping Agency Prohibited List under category S2, which covers peptide hormones and growth factors. It is banned both in and out of competition. Any athlete governed by WADA or a similar body should treat TB-500 as prohibited and confirm with their compliance authority before using it.

The takeaway for a patient is straightforward. TB-500 is not an approved drug, and it will not be one soon. What exists is a well-characterized endogenous peptide with an encouraging early human safety record, a large preclinical literature, and no completed efficacy trial. If you pursue it, do so with a prescription, through a licensed compounding pharmacy, and with clear eyes about the evidence. At PeRx that means the BPC/TB-500 combination, prescribed by a licensed provider who determines whether it fits your situation.

Frequently Asked Questions

Reviewed by Dr. Cory Mellon, MD · Last reviewed April 2026