TB-500
Thymosin beta-4 fragment, TB4, Tβ4
Synthetic fragment of thymosin beta-4, the standard partner to BPC-157 in healing stacks. Reviews of the literature find no randomised human trials in any musculoskeletal tissue.
Preclinical only
Not approved for any use. Explicitly prohibited by WADA at all times, in and out of competition, and flagged by military and sport anti-doping bodies.
What it is
Thymosin beta-4 is a naturally occurring 43-amino acid protein present in most human cells and in wound fluid. TB-500 is a shorter synthetic fragment containing the actin-binding region - the part believed to carry the regenerative activity. The names are used interchangeably in the market; they are not the same molecule.
Mechanism
Thymosin beta-4's primary known function is sequestering G-actin, regulating the actin cytoskeleton that cells use to move. Downstream of that: cell migration into wound sites, angiogenesis, reduced inflammatory signalling, and stem cell recruitment. Full-length Tβ4 has genuinely been studied in humans - for dry eye disease and for cardiac repair after infarction.
The evidence position
A 2026 scoping review is the clearest statement of where things stand. Searching for human interventional studies of administered Tβ4 or TB-500 in tendon, ligament, muscle, bone, cartilage, adipose graft or spinal disc, it identified none. Not weak trials - no trials.
The review's own conclusion is that the published literature does not match how these compounds are discussed in clinical, performance and consumer settings. That mismatch is the single most useful thing to know about TB-500.
The human work that does exist is on full-length Tβ4 for unrelated indications, and it does not transfer to a fragment injected for a hamstring strain.
Practical notes
- The BPC-157 pairing is theoretical. The rationale - different mechanisms, therefore complementary - is reasonable pharmacological reasoning and has never been tested in a human.
- Systemic, not local. Unlike BPC-157, TB-500 is generally administered systemically; the actin/migration mechanism does not obviously benefit from site-specific injection.
- Absolutely disqualifying for tested athletes. TB-500 is prohibited at all times and is detectable.
- The lethargy report is consistent enough across users to be worth planning around - dosing before a rest day is common practice.
Side effects and warning signs
Commonly reported
- Injection-site irritation
- Lethargy or a flu-like feeling in the day after dosing, commonly reported
- Head rush shortly after injection
- No systematic human safety data exists
Stop and get medical help
- Any known or suspected malignancy - thymosin beta-4 promotes cell migration and angiogenesis, and its role in tumour biology is an active research question, not a settled one
- Signs of injection-site infection
Sources
From the community
Discussion for this compound concentrates in r/Peptidesource and r/PeptideForum.
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