TB-500
Thymosin Beta-4 fragment
TB-500 is a gray-market injectable peptide sold to athletes and bodybuilders as a "healing" and recovery aid. Chemically it is not full-length thymosin beta-4 (Tβ4); it is a synthetic, N-terminally acetylated 7-amino-acid fragment (Ac-LKKTETQ), corresponding to residues 17-23 of Tβ4 — the actin-binding/cell-migration active site. The single most important safety fact is that there are no published human clinical trials of TB-500 (the fragment) for any indication, at any dose, by any route. The human trial evidence that vendors cite actually studied a different molecule — full-length recombinant Tβ4 — given topically (skin/eye ulcers) or intravenously under medical supervision, not the self-injected fragment. The main risks therefore stem largely from the unknown: no established safe dose, no human pharmacokinetics, no long-term safety data, and no purity/sterility guarantees for material sold outside regulatory oversight (contamination, endotoxin, and injection-site infection risk). A specific theoretical concern is that the peptide's core biological action is to promote cell migration and angiogenesis (new blood vessel growth), which could, in principle, feed occult or existing tumors — a risk that has never been characterized in humans. It is not an approved human drug. Evidence for TB-500 in humans is graded D (preclinical/mechanistic and analogy to a related molecule only).
Mechanism of action
Pharmacokinetics
Not established in humans for the TB-500 fragment. As a small unprotected peptide it is expected to be rapidly degraded by plasma and tissue peptidases (minutes-to-hours range), but no human PK data exist.
Unknown in humans. Vendor dosing schedules (e.g., twice-weekly) are not supported by any human PK study. In horses given a single 10 mg dose, the acetylated peptide and metabolites remained detectable in plasma/urine, indicating measurable but short systemic exposure.
Marketed for subcutaneous or intramuscular self-injection after reconstitution of lyophilized powder. Note: the only human efficacy/safety data on the parent molecule (full-length Tβ4) used topical or intravenous administration under medical supervision, not self-injection of the fragment.
Presumed proteolytic cleavage into constituent amino acids/short metabolites with renal elimination of fragments; characterized only in equine samples, not in humans. This entry is for washout/monitoring context, not for evading anti-doping testing.
For monitoring and washout planning, not drug-test evasion.
Physiological & performance effects
- Marketed and used off-label for accelerated soft-tissue/tendon/muscle injury recovery and reduced inflammation; these benefits are not demonstrated for the TB-500 fragment in any human trial.
- Full-length thymosin beta-4 (a different, larger molecule) accelerated closure of chronic dermal ulcers in Phase 2 trials and is being investigated for corneal and cardiac repair — these results cannot be assumed to transfer to the self-injected TB-500 fragment.
- Core biological actions (from mechanism/animal data): promotes cell migration, angiogenesis, collagen deposition, stem/progenitor cell mobilization, and dampens inflammation.
- No validated performance-, strength-, or physique-enhancing effect has been established in humans.
Adverse effects by system
No human adverse-event data for the TB-500 fragment. Theoretical concern: because the peptide promotes angiogenesis, effects on vascular remodeling are plausible but uncharacterized. In supervised trials of the related full-length Tβ4 (including a small STEMI stem-cell study and topical ulcer trials) no severe cardiovascular complications were attributed to the peptide, but this does not establish safety of the self-injected fragment.
No human hepatotoxicity data. As a peptide it is not a known direct hepatotoxin, but liver effects of the gray-market fragment are simply unstudied.
No known hormonal or hypothalamic-pituitary-gonadal (HPTA) activity; TB-500 is not a steroid, SERM, or gonadotropin and is not mechanistically expected to suppress testosterone. No human data confirm the absence of endocrine effects.
No human reproductive, fertility, pregnancy, or lactation safety data. Should be considered contraindicated in pregnancy and breastfeeding by default due to absent data plus pro-angiogenic activity.
No known or reported neuropsychiatric effects; no human data.
No human renal safety data. Peptide fragments are renally cleared; effects on the kidney are uncharacterized.
No human hematologic adverse-event data. Endogenous Tβ4 is abundant in platelets and involved in clot/repair biology; any effect of the exogenous fragment on coagulation or blood counts is unstudied.
Injection-site reactions (pain, redness, swelling), and — as with any non-sterile self-injected gray-market product — risk of injection-site infection, abscess, or cellulitis from contaminated or improperly reconstituted material. Systematic data are lacking.
HPTA suppression & recovery
Suppression: None expected mechanistically; no human data
TB-500 is not a hormone, anabolic steroid, or SERM and has no known action on the hypothalamic-pituitary-gonadal axis, so HPTA suppression and post-cycle recovery are not anticipated concepts for this compound. No single-SERM or any SERM protocol is applicable or advised. Anyone with concerns about hormonal status, fertility, or recovery — especially if stacking TB-500 with agents that do suppress the HPTA — should consult a qualified endocrinologist and rely on bloodwork rather than assumptions.
Monitoring
Cadence: Establish a clinician relationship before use; baseline labs, then clinical review if any symptoms develop. There is no evidence-based monitoring schedule because the compound is unstudied in humans — clinician judgment governs.
- Fever, spreading redness, warmth, swelling, or pus at an injection site (possible infection/abscess — seek urgent care)
- New or rapidly changing lumps, masses, or unexplained weight loss (evaluate for malignancy)
- Chest pain, shortness of breath, palpitations, or signs of abnormal clotting
- Signs of allergic reaction: rash, hives, swelling, difficulty breathing (seek emergency care)
- Jaundice, dark urine, right-upper-quadrant pain, or unexplained fatigue (possible liver injury)
Contraindications
- Pregnancy and breastfeeding (no safety data; pro-angiogenic peptide) — default contraindicated
- Active, prior, or suspected malignancy, or strong cancer risk factors — theoretical risk that pro-angiogenic/pro-migratory activity could support tumor growth or metastasis (uncharacterized in humans)
- Any use is outside regulatory approval; the compound is not an approved human drug
- Use of non-sterile, non-pharmaceutical-grade, or unverified gray-market material (infection, endotoxin, contamination risk)
- Known hypersensitivity to the peptide or excipients
Interaction profile
- ContraindicatedWith DNP: Additive cardiovascular strain
Check a specific combination in the interaction checker.
Reducing harm & when to stop
- Understand the core mismatch: the reassuring human trial data circulated online are for full-length thymosin beta-4 given topically or IV under medical supervision — not for the self-injected TB-500 fragment, which has zero human trials. Do not treat those trials as evidence that self-injecting TB-500 is safe.
- Because the compound is unstudied in humans, there is no known safe dose; any dose carries uncharacterized risk. This monograph does not provide a recommended or optimized dose.
- Screen for cancer risk before considering use and avoid entirely with any active/prior malignancy, given the peptide's pro-angiogenic, pro-migratory biology.
- Do not use in pregnancy or while breastfeeding.
- Gray-market injectables carry contamination, endotoxin, and sterility risks; unverified material can cause infection independent of the peptide itself.
- Establish care with a clinician and get baseline bloodwork (CBC, liver, renal) before use; involve an endocrinologist if combining with hormone-active agents.
- Stop immediately and seek medical care for injection-site infection (fever, spreading redness, pus), allergic reaction (swelling, trouble breathing), new lumps/masses or unexplained weight loss, chest pain/shortness of breath, or signs of liver injury (jaundice, dark urine).
- This is a health note, not legal or procurement advice; if you are a tested athlete or in a regulated context, verify current anti-doping/prohibited-substance status with the relevant authority yourself.
Citations (8)
Every clinical claim above is tied to a primary source. Overall evidence grade D — this compound lacks adequate human data; claims rest on preclinical or mechanistic evidence.
- 01
TB-500 is a synthetic, N-terminally acetylated version of the LKKTETQ peptide (residues 17-23 of thymosin beta-4), which is the active actin-binding site responsible for actin binding, cell migration and wound healing; a single 10 mg dose was detectable in equine plasma/urine.
PreclinicalPMID 23084823 ↗
- 02
The formulation TB-500 was identified as containing the N-terminal acetylated 17-23 fragment of human thymosin beta-4 (Ac-LKKTETQ), confirming its chemical identity as a fragment rather than full-length Tβ4.
PreclinicalDOI 10.1002/dta.1402 ↗
- 03
Human safety data for the unapproved TB-500 (thymosin beta-4 fragment) peptide are scarce, its use in sports medicine is driven by patient demand rather than evidence, and there is potential for serious harm to patients.
ReviewSafety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance.DOI 10.1007/s40279-026-02437-0 ↗
- 04
Thymosin beta-4's mechanism includes G-actin sequestration/actin regulation, promotion of cell migration, angiogenesis, collagen deposition, stem/progenitor cell mobilization, and anti-inflammatory and anti-apoptotic effects.
- 05
Full-length thymosin beta-4 accelerated dermal healing in Phase 2 trials of pressure and venous stasis ulcers and is being developed for corneal and cardiac repair — human data pertain to the full-length molecule, not the TB-500 fragment.
- 06
In a double-blind, placebo-controlled Phase 2 randomized trial (n=73), topically administered full-length thymosin beta-4 for venous stasis ulcers had a safety/tolerability profile comparable to placebo.
- 07
Full-length thymosin beta-4 was developed for ischemic heart disease with Phase 1 assessment of safety, tolerability and pharmacokinetics conducted by intravenous administration in a supervised clinical setting (parent molecule, not the self-injected fragment).
ReviewPMID 17947592 ↗
- 08
In a 10-patient pilot randomized study, thymosin beta-4-pretreated endothelial progenitor cell transplantation in STEMI patients was feasible with no severe procedure-related complications during follow-up.
Last reviewed 2026-07-06 · Verified against PubMed · Educational, not medical advice