Overview

Thymosin beta-4 (Tβ4) is a natural 43-amino-acid protein found in almost every cell, where it helps control the cell's internal skeleton and cell movement. "TB-500" is a lab-made product sold online that is usually described as a short fragment (LKKTETQ) of Tβ4, though what is in the vial varies. Nearly all human studies tested full-length Tβ4 (as eye drops, skin gel or IV infusion), not TB-500.

How it works

Established for Tβ4 in cells: it binds G-actin (single actin units) and controls how much actin is available to build filaments, which affects how cells move and change shape ¹. Proposed from animal and lab studies: it promotes cell migration into wounds, new blood vessel growth, and reduced inflammation and scarring ¹. The LKKTETQ segment is the actin-binding region, and it is assumed (not well proven) that the fragment shares the full protein's healing effects.

What research shows

Human data are for full-length Tβ4, not TB-500. FDA says it found no human exposure data for products containing the Tβ4 fragment ⁶.
Phase 2 randomized trial of RGN-259 0.1% eye drops in dry eye (n=72, controlled adverse environment model): the two main goals were not met, but some secondary measures (corneal staining, discomfort during the challenge) improved vs placebo ².
Phase 3 randomized trial (SEER-1) of RGN-259 0.1% eye drops in neurotrophic keratopathy: stopped early for slow enrollment (n=18); 6 of 10 treated eyes vs 1 of 8 placebo fully healed by day 29, which narrowly missed statistical significance ¹³.
Compassionate-use case series of Tβ4 eye drops in non-healing neurotrophic corneal defects (n=9): 6 patients with larger defects healed ⁵.
Phase 2 dose-ranging trial of RGN-137 topical gel in venous leg ulcers (n=72; 0.01%, 0.03%, 0.1%): no dose beat placebo with statistical significance; the middle dose showed a trend toward faster healing ³¹⁴.
Phase 1 IV study in healthy volunteers (n=40): single and 14-day daily doses of 42-1260 mg were well tolerated, with no dose-limiting toxicity ⁴.
No published results were found for RegeneRx's RGN-137 trial in epidermolysis bullosa.
Animal studies report benefits in heart, skin, eye and nerve injury models ¹.

Doses studied in people

Study or label	Dose used	Source
Phase 2 RCT of RGN-259 in dry eye (n=72; full-length Tβ4)	0.1% Tβ4 eye drops, 1-2 drops twice daily for 28 days	²
Phase 3 RCT (SEER-1) of RGN-259 in neurotrophic keratopathy (n=18; full-length Tβ4)	0.1% Tβ4 eye drops, five times daily	¹³
Phase 2 RCT of RGN-137 in venous leg ulcers (full-length Tβ4)	Topical gel at 0.01%, 0.03% or 0.1% Tβ4 for up to 84 days	¹⁴
Phase 1 IV study in healthy volunteers (n=40; full-length Tβ4)	Single IV doses of 42, 140, 420 or 1260 mg, and the same doses daily for 14 days	⁴

All human doses come from studies of full-length thymosin beta-4; there is no published human dosing data for the TB-500 fragment, and doses circulating online are not from trials.

Read this first: these are the amounts given to participants in published studies or written on official prescribing labels, reported for reference. They are not recommendations. Trial doses were chosen for specific patients under medical supervision, and a dose that is safe in one person can be harmful in another.

Weekly protocol

How the schedule looks week by week. Each chart says where it comes from: a prescribing label, a clinical trial, or a protocol commonly reported online.

Commonly reported loading and maintenance protocol

Commonly reported, not studied

One week

D1D2D3D4D5D6D7

Twice weekly while loading, then once weekly · Subcutaneous or intramuscular injection

Syringe units (U-100)

Vial Water added

Dose by week

1.0–1.5 mg per injection, twice weeklyLoading · wk 1–6

1–2 mg once weeklyMaintenance · wk 7–12

Supplies for one course (estimate)

Counts only. This site does not sell or link to supplies.

Course: Loading 4–6 weeks, then maintenance; 2–4 weeks off before repeating
Note: No human data exist for the TB-500 fragment; human trials used full-length thymosin beta-4. Reported loading doses range from about 1 mg up to 2–2.5 mg, 2–3 times a week.
Source: Peptidepedia: TB-500 dosage guide
Also: Peptide Protocol Wiki: TB-500 dosing protocols

PeptideDosages.com daily titration

Commonly reported, not studied

One week

D1D2D3D4D5D6D7

Once daily · Subcutaneous injection

Syringe units (U-100)

Vial Water added

Dose by week

500 mcgwk 1–2

600 mcgwk 3–4

750 mcgwk 5–8

1,000 mcgwk 9–12

Supplies for one course (estimate)

Counts only. This site does not sell or link to supplies.

Course: 8–12 weeks (optional extension to 16)
Note: The same site's TB-500 + BPC-157 stack page instead uses 1.25 mg twice weekly for 4 weeks, then once weekly to week 12.
Source: PeptideDosages.com: TB-500 (5 mg vial) dosage protocol

Reference only, not a recommendation. Charts marked "commonly reported" describe what public sources say people use. They have not been tested in trials, and their safety and effect are unknown. Label and trial schedules were set for specific patients under medical supervision. Use the calculator only to understand the arithmetic.

Vial math

Many research vials hold 5 or 10 mg of powder. This table shows how much ends up in each mark on a U-100 insulin syringe for common amounts of added liquid. It is arithmetic only, not a dose.

Vial	Liquid added	Concentration	Per unit (0.01 mL)
5 mg	1 mL	5 mg/mL	50 mcg	Open in calculator
5 mg	2 mL	2.5 mg/mL	25 mcg	Open in calculator
5 mg	3 mL	1.67 mg/mL	16.7 mcg	Open in calculator
10 mg	1 mL	10 mg/mL	100 mcg	Open in calculator
10 mg	2 mL	5 mg/mL	50 mcg	Open in calculator
10 mg	3 mL	3.33 mg/mL	33.3 mcg	Open in calculator

More sizes: all vial sizes · How this works: Syringes and units · Reconstitution guide.

Safety

No published human safety data exist for TB-500 itself; FDA says it lacks key safety information and flags possible immune reactions from aggregation and impurities ⁶.
Full-length Tβ4 was generally well tolerated in small trials of eye drops, skin gel and IV infusion (up to 1260 mg/day for 14 days) ²³⁴¹³.
Lab and tissue studies associate high Tβ4 levels with tumor growth and spread in some cancers, so promoting it raises a theoretical cancer concern ¹². An earlier report that FDA staff raised a cancer signal at the July 2026 advisory meeting could not be confirmed in the meeting coverage reviewed.
Products sold as TB-500 may contain the fragment, full-length Tβ4, or something else; contents are unverified.
Long-term safety is unknown.

Report side effects of any drug or product to the FDA through MedWatch. For a possible poisoning in the US, call Poison Control at 1-800-222-1222.

Legal status

FDA: Neither TB-500 nor thymosin beta-4 is FDA-approved; RegeneRx's Tβ4 products remain investigational ¹¹⁰.
Compounding: "Thymosin Beta-4, Fragment (LKKTETQ)" was in 503A Category 2 from 2023 until about April 22, 2026, when it was removed after the nomination was withdrawn; removal does not make it legal to compound ⁷. On July 23, 2026 the PCAC voted 8-6 (1 abstention) to recommend adding TB-500 to the 503A bulks list for wound healing, against FDA staff advice; advisory only, rulemaking needed ⁸⁹¹⁰. An interim access policy was under White House review in October 2026 ⁹. Update: on October 28, 2026 HHS issued an interim enforcement discretion policy covering TB-500 / Thymosin beta-4: HHS does not intend to take action against 503A pharmacies, federal facilities or physicians that compound it under set conditions (patient-specific prescription, FDA-registered ingredient source with a certificate of analysis, single ingredient, adverse-event reporting), limited to injection under the skin or into muscle. This is not FDA approval, is non-binding, and applies only until a final rule on the 503A bulks list ¹⁵¹⁶.
Sports (WADA): Prohibited at all times; S2.3 lists "Thymosin-β4 and its derivatives e.g. TB-500" on the 2026 list ¹¹.
Other: Not a DEA-controlled substance. Widely detected in equine and human anti-doping testing.

Rules change often. See Legal status of peptides for how these categories work.

History

Tβ4 was characterized in the early 1980s by Allan Goldstein's group while studying thymus extracts ¹. RegeneRx Biopharmaceuticals developed full-length Tβ4 as RGN-259 eye drops (dry eye, neurotrophic keratopathy), RGN-137 topical gel (skin wounds) and RGN-352 injectable (heart); RGN-259 reached phase 3 trials; none has been approved ¹²³⁵¹³. The fragment sold as TB-500 became popular in horse racing and bodybuilding. FDA placed "Thymosin Beta-4, Fragment (LKKTETQ)" in 503A Category 2 in 2023 and removed it in April 2026 after the nomination was withdrawn ⁶⁷.

Common questions

Is TB-500 the same as thymosin beta-4?

Not exactly. Thymosin beta-4 is a natural 43-amino-acid protein, while TB-500 is usually described as a short fragment of it, and almost all human studies used the full-length protein ¹⁶.

Is TB-500 FDA-approved?

No. Neither TB-500 nor thymosin beta-4 is FDA-approved, and RegeneRx's thymosin beta-4 products remain investigational ¹¹⁰.

What does the human research show?

Small trials of full-length thymosin beta-4 eye drops and skin gel gave mixed results, with some secondary measures improving but main goals not met ²³¹³¹⁴. FDA says it found no human exposure data for products containing the TB-500 fragment ⁶.

What doses were studied in people?

All human doses come from full-length thymosin beta-4, for example 0.1% eye drops, 0.01% to 0.1% skin gel, and IV doses of 42 to 1260 mg in healthy volunteers ²⁴¹³¹⁴. There are no published human doses for TB-500 itself ⁶.

Is TB-500 safe?

There are no published human safety data for TB-500, and FDA flags possible immune reactions from clumping and impurities ⁶. Full-length thymosin beta-4 was generally well tolerated in small trials, but lab studies link high levels to some cancers' growth, a theoretical concern ²³⁴¹²¹³.

Is TB-500 banned in sport?

Yes. WADA's 2026 list prohibits it at all times under S2.3, which names thymosin-beta-4 and its derivatives such as TB-500 ¹¹.

Sold in blends and stacks

BPC-157 + TB-500 GLOW blend KLOW blend Tri-Heal blend

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GHK-Cu is a tiny three-amino-acid peptide (GHK) bound to copper.