TB-500

Typical Range

Protocols discussed for injection typically use 2–2.5 mg per dose, with a front-loading phase of 2.5 mg twice weekly for 4–6 weeks followed by maintenance of 2 mg every 1–2 weeks. Some protocols use 5 mg once weekly during loading. These numbers come from community and clinician-reported protocols rather than human dose-ranging trials; the animal literature uses widely varying doses on a mg/kg basis that do not translate cleanly to human flat doses.

Frequency

During a loading phase, twice-weekly injection is the most commonly described cadence. After 4–6 weeks many protocols shift to once weekly or once every two weeks for maintenance. The rationale for infrequent dosing versus daily dosing is pharmacokinetic: thymosin beta-4's circulating half-life is short, but its effects on cell migration and actin remodeling are thought to persist beyond plasma clearance.

Timing Considerations

Cycle Length

A typical discussed cycle is a 4–6 week loading phase followed by a lower-frequency maintenance phase or a washout. Some clinicians use 4–8 week courses tied to the healing timeline of a specific injury, then stop. Continuous long-term use has not been studied in humans.

Protocol Notes

TB-500 is typically supplied as a lyophilized powder requiring reconstitution in bacteriostatic water. A common reconstitution is 5 mg of peptide in 2–3 mL of bacteriostatic water; with 2 mL that yields 2,500 mcg/mL, meaning a 2 mg dose is 0.8 mL on an insulin syringe. Subcutaneous injection into the abdominal fat pad is the most common route; intramuscular injection near the affected tissue is also used in musculoskeletal protocols. One point of confusion worth flagging: the products sold as 'TB-500' on the research-chemical market may correspond to different synthetic fragments (commonly the N-acetylated 17-23 region of TB-4 identified in doping control literature) rather than the full 43-amino-acid thymosin beta-4 used in RegeneRx's clinical work. This means that dosing extrapolated from TB-4 clinical trials does not map cleanly to TB-500 products, and purity and identity should not be assumed. TB-500 is commonly stacked with BPC-157 in recovery protocols. There is no human trial evidence for the combination; the rationale is mechanistic complementarity (actin-driven cell migration plus angiogenesis and growth factor modulation) rather than demonstrated additive benefit.

Onset

Anecdotal reports from injury-recovery use commonly describe initial subjective improvement (reduced pain or stiffness) within 1–2 weeks of starting a loading protocol. Tissue-level healing signals are inherently slower and are typically described over 3–4 weeks rather than days. Human trials of full-length TB-4 in dermal and corneal wound healing saw measurable endpoint changes on the order of several weeks.

Peak Effect

Peak effect is typically described in the 4–8 week window corresponding to the end of a standard loading phase. This aligns with the tissue-remodeling timelines observed in preclinical wound-healing models. Whether continued dosing beyond this window adds benefit or simply maintains a plateau is not established.

After Discontinuation

Thymosin beta-4's plasma half-life is short (minutes to a few hours), but its downstream effects on actin dynamics, cell migration, and tissue remodeling persist longer. Most users describe benefits that persist after cessation provided the underlying tissue has healed; ongoing anti-inflammatory effects tend to fade within weeks of discontinuation. Rebound effects have not been systematically described.

Bloodwork & Labs

• •hs-CRP — systemic inflammation proxy; useful when the injury context is inflammatory
• •ESR — slower-moving inflammation marker, pairs with hs-CRP
• •CBC — tracks hematocrit, since TB-500 has documented angiogenic activity, and rules out confounding issues
• •Comprehensive metabolic panel — baseline only, for hepatic anchor

Functional & Performance Tests

• •Standardized pain score (VAS or NRS) on the target tissue, recorded daily
• •Goniometer-measured range of motion for the affected joint
• •Sport- or task-specific functional test (single-leg hop, grip strength, walking distance, throwing velocity — pick one your injury is actually limited by)
• •Diagnostic ultrasound or MRI at baseline and end-of-cycle for structural injuries

When to Test

Symptom and functional tracking daily. hs-CRP and CBC at baseline and 4–6 weeks. Imaging at baseline and end of a 4–6 week cycle if accessible.

Interpretation & Notes

As with BPC-157, TB-500's claimed effect is tissue-local and slow — the measurement job is functional documentation rather than a blood-marker chase. The credible at-home setup is a disciplined pain-and-function log paired with pre- and post-cycle imaging. hs-CRP moves when the injury context is systemically inflammatory and can stay flat in mechanical injuries where the peptide may still be helping. TB-500's theoretical angiogenesis signal is the reason the oncology-risk discussion exists — if you have a cancer history or active screening concern, this warrants a clinician conversation before use, not a post-hoc lab. There is no validated serum marker that tracks TB-500 activity. Basic panels via LabCorp, Quest, Marek Health, or Ulta Lab Tests; imaging typically needs a clinician order.

United States

TB-500 and thymosin beta-4 are not FDA-approved for any indication. Full-length recombinant TB-4 (RGN-259, RGN-137) has been studied in clinical trials under RegeneRx and its partners — up to Phase 3 for the RGN-259 eye drops (ARISE in dry eye, SEER in neurotrophic keratopathy) — but has not advanced to approval. TB-500 has historically been available through compounding pharmacies and research-chemical suppliers; following the FDA's 2023 review of peptides considered for 503A compounding, access tightened, though enforcement varies. Research-chemical channel sales are not intended or authorized for human use. Two 2026 developments moved the compounding picture, in the same direction but not as far as often reported. Effective 22 April 2026 TB-500 came off FDA's Category 2 list as one of 17 bulk substances whose nominators withdrew their nominations, and at the Pharmacy Compounding Advisory Committee meeting of 23–24 July 2026 the committee voted 8–6, with one abstention, to recommend TB-500 for inclusion on the Section 503A Bulk Drug Substances list. It was one of six peptides recommended out of seven nominated — with BPC-157, KPV, MOTS-c, semax, and epitalon — and only emideltide (DSIP) was voted against. FDA's own reviewers had argued against addition, citing short and underpowered studies. Neither step authorizes compounding. Removal from Category 2 was not authorization, PCAC recommendations are non-binding, and formal addition to the bulks list requires notice-and-comment rulemaking that has not been completed. The practical position remains that licensed US compounding pharmacies have no clear authorization to prepare TB-500 for human use, notwithstanding a favourable advisory vote. On 28 October 2026 that ambiguity was partly resolved, though not in the way most coverage implied. HHS filed an enforcement discretion policy — Docket HHS-OASH-2026-0496, RIN 0910-ZD94, published in the Federal Register on 30 October as FR Doc. 2026-22192 and signed by Secretary Kennedy — stating that it does not intend to take enforcement action against a state-licensed pharmacy, federal facility or licensed physician that compounds a drug product using one of six named peptide bulk drug substances: BPC-157, TB-500, epitalon, KPV, MOTS-c and semax. For TB-500 the covered identity is the acetate salt, limited to subcutaneous and intramuscular injection. The discretion is narrow and conditional. The active ingredient must come from an FDA-registered manufacturer operating under CGMP, with the manufacturing facility identified on the certificate of analysis — a repacker's or distributor's registration does not satisfy this — and must be supported by analytical testing covering identity including sequence, purity, potency, impurities, residual solvents, elemental impurities, microbial content and endotoxins. Each compounded product may contain only one covered active ingredient. That single-ingredient rule has a consequence worth spelling out, because it cuts against the most common way these peptides are actually used: a compounded product combining two listed peptides — BPC-157 with TB-500, for instance — falls outside the policy even though each is individually covered. Section 503A's patient-specific prescription requirement still applies, so this is not a licence for commercial-scale production, and the policy does not extend to 503B outsourcing facilities. Compounders must report product details to FDA and state authorities, report adverse events and quality problems through MedWatch, and label products with reporting instructions and the statement that this is a compounded drug product not for resale. What it is not is an approval. The notice states that FDA's future rulemakings may propose adding some or all of these peptides to the 503A bulks list, that the policy does not establish any rights for any person and is not binding on HHS or the public, and that HHS may revisit it if a safety signal or product quality issue arises. TB-500 is still not on the 503A bulks list, nothing has been shown to be safe or effective, and FDA's own reviewers had recommended against all seven nominated peptides. The comment period runs roughly two weeks from publication, and the rulemaking that would make any of this durable is generally estimated at 12 to 24 months.

International

No major regulator (EMA, MHRA, TGA, Health Canada) has authorized TB-500 or thymosin beta-4 as a medicine. Australia's TGA treats it as a Schedule 4 prescription-only substance and has taken enforcement action. Most other jurisdictions treat it as an unapproved investigational agent, and importation of personal-use quantities is restricted in several countries.

Sports & Competition

TB-500 is explicitly prohibited by WADA under S2.3 (growth factors and growth factor modulators), which names 'thymosin-β4 and its derivatives e.g. TB-500' on both the 2026 list and the 2027 list in force from January 1, 2027. Prohibited at all times, in and out of competition. Multiple athletes — including high-profile cases in horse racing and human sport — have been sanctioned for TB-500 use. Doping-control laboratories have developed and validated assays specifically targeting the TB-500 synthetic fragment. Athletes subject to WADA code, USADA, UKAD, or equivalent bodies should treat TB-500 as unambiguously banned.