TB-500: The Only Dated Recovery Curve on This Desk

The short version

TB-500 is a synthetic seven-amino-acid fragment, written Ac-LKKTETQ. It copies a small piece — residues 17 to 23 — of a natural 43-amino-acid protein called thymosin beta-4, which the body uses to organise actin, the internal scaffolding that lets cells change shape and move.

Here is the fact that governs everything else on this page. Almost all the encouraging research credited to 'TB-500' was actually done with the whole parent protein, not with the short fragment that suppliers sell under that name. The two are different molecules of very different size, and it has never been shown that the fragment reproduces what the whole protein does.

That matters most for timing. This corpus contains exactly one study that reports a dated recovery curve: in rats recovering from a stroke, treatment begun a day after the injury improved neurological function measurably from day 14 through day 56 ^[9]. It is a genuine timeline. It is also a rat timeline, and it used the parent protein.

What it is

TB-500 is a synthetic, N-terminally acetylated heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, corresponding to residues 17 to 23 of thymosin beta-4 (Tβ4, gene TMSB4X). That LKKTETQ stretch is the conserved actin-binding motif shared across the beta-thymosins. It also appears under the names Ac-LKKTETQ, the thymosin beta-4 17-23 fragment, and — in veterinary settings — TB-500 or TB1000.

The identity distinction is not pedantry, and this corpus flags it wherever a finding used the full-length protein. In commerce and in the analytical and anti-doping literature, 'TB-500' denotes the roughly 889-dalton heptapeptide. Most published efficacy research uses full-length recombinant or synthetic thymosin beta-4, which is roughly 4,963 daltons — more than five times the mass. Reading results from one as results for the other is an extrapolation nobody has validated.

TB-500 has no approved therapeutic indication and is not approved by the FDA for human use. The World Anti-Doping Agency prohibits it under its peptide, growth-factor and tissue-repair categories, in and out of competition for the relevant classes, and anti-doping laboratories have developed liquid-chromatography mass-spectrometry assays to detect it in both equine and human samples. It is sold by research suppliers for laboratory use only. Some jurisdictions, including Australia and New Zealand, classify it as a prescription medicine.

How it works

The mechanism belongs to the parent protein and is unusually well resolved at the structural level. X-ray crystallography of a gelsolin-domain-1–thymosin-beta-4 hybrid bound to actin, solved at 2 ångström resolution, established that thymosin beta-4 forms a one-to-one complex with monomeric (globular) actin and sequesters it by capping both ends of the monomer, preventing it from polymerising; the WH2 actin-interacting motif underlies the interaction ^[12]. That is the LKKTETQ region — the part TB-500 reproduces.

From that single biochemical action a broad functional account follows. A 2012 review consolidates it: thymosin beta-4 binds actin and promotes cell mobilisation, migration and stem-cell activity; it decreases myofibroblast number, which reduces scar formation; it is released by platelets and macrophages after injury, where it limits apoptosis, inflammation and microbial growth; and it promotes angiogenesis — together the rationale for clinical trials in dermal wounds, corneal injury and cardiac and central-nervous-system repair ^[10].

Read against the clock, this is a mechanism that maps onto the earliest phase of healing. A protein released by platelets at the moment of injury, buffering the actin pool that cells need in order to crawl into a wound, is doing inflammatory- and proliferative-phase work. Whether the isolated seven-amino-acid fragment reproduces the full protein's effects at the quantities used in peptide research has not been established in any controlled human trial.

What the research shows, and when it was measured

The one dated curve. In male Wistar rats with embolic middle cerebral artery occlusion, intraperitoneal thymosin beta-4 was given at 2, 12 or 18 mg/kg beginning 24 hours after the stroke and repeated every three days for four further doses. Neurological function improved at 2 and 12 mg/kg, with the difference significant from day 14 through day 56 (p<0.05); 18 mg/kg produced no significant benefit, and the authors modelled an optimal dose of approximately 3.75 mg/kg ^[9]. Every element of that sentence matters to this desk. Treatment started a day after injury, not before it. The benefit was not detectable at the first assessments and was still present at day 56. And the dose-response was non-monotonic — the highest dose did nothing, which is the opposite of what a loading rationale would predict.

The one human interval. In a randomised, placebo-controlled Phase 1 study, synthetic thymosin beta-4 was given intravenously to 40 healthy volunteers in four cohorts of ten, as a single dose and then daily for 14 days at 42, 140, 420 or 1,260 mg. It was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities and no serious adverse events, and pharmacokinetics were dose-proportional with half-life increasing as the dose rose ^[11]. This is a 14-day tolerability window in healthy people using the full-length protein. It is not a healing measurement, and it is not a study of the fragment.

The structural anchor. The 2 ångström crystal structure fixes the one-to-one actin-sequestration mechanism ^[12] — a fact about molecular geometry, with no time axis at all.

The class verdict. A 2026 Sports Medicine narrative review of approved and unapproved peptide therapies for musculoskeletal injury and athletic performance, listing TB-500 and thymosin beta-4 alongside BPC-157 among the unapproved compounds, concluded that many show favourable tissue-repair outcomes in animal models but that rigorous human safety data are scarce, that there is potential for serious harm, and that these compounds operate largely outside regulatory oversight ^[8].

There are no completed controlled human trials of the TB-500 heptapeptide for any indication. So the time axis for the fragment specifically is empty: no measured onset, no measured duration, no measured persistence.

Reported effects, cautions and safety

The community accounts below are anecdotal, not clinical evidence. They come from peptide-user forums, athletic and biohacker blogs, research-supplier pages and qualitative summaries of online discussion, they carry no doses here, and none of their intervals has been measured.

The most common reason people in research-use communities reach for TB-500 is recovery from tendon, ligament and soft-tissue injury, very commonly reported with the observation that the reported timelines vary widely from one person to another. Reduced joint pain and stiffness with better range of motion is frequently reported on a several-week framing; improved general flexibility and physical resilience is frequently reported, often noticed around three to four weeks in; a vaguer sense of reduced inflammation or calmed post-exercise soreness is occasionally reported; better wound and skin healing is occasionally reported; and hair regrowth over four to eight weeks is rarely reported, usually by people also using other things at the same time. On the adverse side, injection-site redness, swelling or aching is very commonly reported and usually described as gone within a day or two; temporary tiredness or lethargy in the first day or two is frequently reported and is the most consistent systemic complaint; head rush, lightheadedness or headache shortly after a dose is occasionally reported; a brief flu-like feeling in the first day or two is occasionally reported; and nausea, a heightened awareness of an existing injury during the first week or two, and short-lived mood changes are each rarely reported.

The documented cautions are substantial. Human safety is essentially unstudied: no completed controlled human trial of the heptapeptide exists for any use, and the 2026 sports-medicine review concluded that compounds like it show animal-model promise but have scarce human safety data, potential for serious harm, and little regulatory oversight ^[8][11]. A theoretical cancer concern is taken seriously because the parent protein is overexpressed in several cancers and has been linked to metastasis and tumour blood-vessel growth, so the same pro-migration and pro-angiogenic actions that may aid repair could in principle support tumour progression. It is prohibited in sport, with confirmed detection methods, so a positive test can end an athlete's eligibility ^[8]. Reported benefits may overstate what the peptide does: in dystrophin-deficient mice, long-term thymosin beta-4 increased the number of regenerating muscle fibres but did not improve muscle strength, cardiac function or fibrosis — more regeneration on paper without better function, which is a direct caution against reading a felt improvement as structural repair. TB-500 is a fragment rather than the whole protein, and applying the parent protein's results to it is unconfirmed ^[10]. Research-grade product identity, purity and sequence are not guaranteed between suppliers. And there are no human safety data for clotting disorders, upcoming surgery, pregnancy, breastfeeding or the still-growing, where the conservative position is avoidance rather than assumed harmlessness.

Where it sits on the repair timeline

TB-500 occupies an odd position. It has the best-resolved mechanism on this desk ^[12], the only dated recovery curve ^[9], and the least evidence that either belongs to the molecule actually being sold.

On phase, the parent protein's biology is early: platelet release at the moment of injury, actin buffering for cell migration, myofibroblast suppression that reduces scarring ^[10]. On duration, the rat stroke study gives a real interval — measurable from day 14, still present at day 56 — but it is a neurological-recovery endpoint in rodents, not a musculoskeletal one in people, and it used the full-length protein ^[9]. On dose-response, the same study delivers the most useful corrective in this corpus: the highest dose tested produced no benefit at all, which undercuts the community practice of front-loading.

The community's own timelines cluster at three to four weeks and beyond. Nothing in the measured record contradicts that, and nothing in it supports it either. The comparison page places this curve beside BPC-157's absent one, and the Wolverine page covers what happens when the two are combined — which, on the evidence, is nothing anyone has measured.