Community injection
Community- Dose
- 2–2.5 mg
- How often
- Twice weekly, then weekly
- How long
- 4–6 weeks, then maintenance
Borrowed from TB-500 guides, which often use the two names interchangeably. Never tested in any study.
Draw 40–50 units5 mg + 1 mL
Human studiesActin-binding repair peptide
Thymosin Beta-4
Tβ4, timbetasin, RGN-259 (eye drops), RGN-137 (gel), NL005
- Common dose
- 2–2.5 mg twice weekly, then weekly
- Cycle
- Load 5 weeks, maintain 6, then 6 off
- Vial sizes
- 5, 10 mg
- Typical draw
- 50 units5 mg with 1 mL, 2.5 mg
The full 43-amino-acid protein that nearly all cells make, also found in blood, tears and wound fluid; it binds actin, part of the cell’s internal skeleton, and helps cells move in to repair tissue. TB-500 is a 7-amino-acid piece of it (residues 17–23).
Evidence. Tested in people as IV infusions, eye drops and wound gels, but never approved. The eye drops missed their main goals in two Phase 3 dry-eye trials (about 1,300 people) and in a European neurotrophic keratitis trial (June 2025); a second keratitis trial, SEER-2, finished in 2026, with top-line results expected around mid-November 2026. In China, an IV recombinant form is in Phase 2 trials for heart attack.
Status
- Approval
- Not approved as a drug in the US or EU. Its eye drops (RGN-259) and a recombinant IV form are still in clinical trials.
- US compounding
- Not nominated for compounding: full-length thymosin beta-4 isn’t on FDA’s 503A category lists (updated May 14, 2026) or its 503B lists. The withdrawn nomination and the July 2026 advisory committee vote concern the TB-500 fragment, which FDA treats as a different substance.
- Sport (WADA 2026)
- Banned in sportS2.3 growth factors and growth factor modulators: “thymosin-β4 and its derivatives e.g. TB-500” are named. Banned at all times.
Category 2 is FDA’s list of bulk substances that may present significant safety risks in compounding. The 503A bulks list adds substances that pharmacies may compound with. Advisory committee votes are advice; FDA makes the final decision. Sport status follows the WADA Prohibited List in force since January 1, 2026; athletes should confirm with their anti-doping organization. Checked October 5, 2026. Status of every compound.
How it works
Thymosin beta-4 is the 43-amino-acid protein nearly all cells make. It binds G-actin, the free single units of a cell’s internal scaffolding, holding a pool cells draw on when they move; in animals it also speeds skin and eye healing and promotes new blood vessels. That mechanism rests on cell and animal work, while the human trials measured healing, not mechanism.
AnimalMainly from cell and animal studies; not shown in people.
Not known
Which of its actions matter in people is unknown, as is what it does over months: the whole-body human data are IV courses of up to 14 days.
Protocol
Trial
Ruff 2010
IV infusion of 42–1,260 mg once daily for 14 days in healthy volunteers, a safety test only.
Trial
SEER-1, 2023
Eye drops: 0.1% solution (RGN-259) 5× daily for 28 days in neurotrophic keratitis; 2–6× daily for 2–4 weeks in dry-eye trials.
Community
No protocol specific to the full protein. Guides often treat it as the same thing as TB-500 and use that schedule: 2–2.5 mg under the skin twice weekly for 4–6 weeks, then about 2 mg weekly.
- Frequency
- 2× per week, then weekly
- Route
- Subcutaneous injection (community); IV, eye drops and skin gel in trials
- Cycle
- No cycle has been studied. Guides apply TB-500’s pattern: about 4–6 weeks of twice-weekly loading, then weekly maintenance, then several weeks off.
Load 5 weeks, maintain 6, then 6 off, shown over 26 weeks
Common protocols
The ways Thymosin Beta-4 is most often run, each tagged with where it comes from.
Eye drops (RGN-259)
Trial- Dose
- 0.1% solution
- How often
- 5× daily (keratitis); 2–6× daily (dry eye)
- How long
- 14–28 days
In 18 people with neurotrophic keratitis, 6 of 10 healed by day 29 vs 1 of 8 on placebo, just short of significance. The dry-eye trials missed their main goals.
Wound gel
Trial- Dose
- 0.01–0.1% gel
- How often
- Once daily on the ulcer
- How long
- Up to 84 days
Phase 2 trials in venous leg ulcers and pressure ulcers. About 1 in 4 venous ulcers closed within 3 months, about the same share as on placebo.
IV safety trial
Trial- Dose
- 42–1,260 mg
- How often
- Once daily by IV infusion
- How long
- Single dose, then 14 days
40 healthy volunteers in four dose groups. No dose-limiting side effects (Ruff 2010). Hospital research only.
Dosing by body weight
Trial0.05–25 mcg/kg. Recombinant thymosin beta-4 (NL005) by IV in Chinese trials: single doses of 0.05–25 mcg/kg in healthy volunteers (Wang 2021); heart-attack trials used 0.25–20 mcg/kg daily for 7 days. Not a subcutaneous dose.
At 70 kg, per dose3.5 mcg–1.75 mg0.1–35 units at 5 mg + 1 mL
Taking it
Where it goes
Community use is injection under the skin of the belly, thigh or upper arm, rotating sites. Trials gave it by IV drip, as eye drops, or as a gel on wounds.
If you miss a dose
No published guidance. Take it when you remember unless the next dose is close, then keep the usual days; don’t double up.
What to expect
- Day 29 (eye drops)
In neurotrophic keratitis, the corneal sore closed in 6 of 10 treated people vs 1 of 8 on placebo (p=0.066); by day 43 the difference was significant (p=0.036).
Trial - Day 15 (eye drops)
In 700 people with dry eye (ARISE-3), corneal staining and discomfort improved no more than on placebo.
Trial - Up to 84 days (wound gel)
12 of 55 venous leg ulcers closed on the gel vs 4 of 17 on placebo; the researchers reported faster healing in ulcers that did close.
Trial - Day 90 (heart attack, IV)
In 96 patients given a recombinant form, heart scar size didn’t differ overall; it was smaller in those whose first dose came within 8 hours of having the artery reopened.
Trial
Side effects and what to do
Eye drops: sting or pain (6.6% vs 4.6% on placebo) and reduced sharpness of vision (3.4% vs 2.0%) in ARISE-3
Usually brief. Stop and see an eye doctor if pain, redness or blurred vision persists.
IV infusions: infrequent, mild to moderate side effects, none dose-limiting up to 1,260 mg a day (Ruff 2010)
Only 14 days were tested, in healthy adults; longer use is unstudied.
Tiredness or headache early on (community reports for TB-500-type products)
Usually fades within 1–2 weeks. Stop if it’s severe.
Injection-site redness, swelling or tenderness (community)
Rotate sites. Spreading redness, heat or pus needs medical care.
Unknown long-term risk, including the theoretical tumor concern
It promotes cell migration and new blood vessels. Avoid with active or past cancer.
Stop and get medical help
Hives, face or throat swelling, trouble breathing, chest pain or fainting; spreading redness, heat or pus at a site; eye pain or vision loss with eye drops; or any new lump.
Who should avoid it
No product label covers thymosin beta-4, so these come from human studies and from precautions based on how it works. Most important first.
- Anyone with active or past cancer
- PrecautionIt drives cell migration and new blood vessels; forcing it up in mouse melanoma cells multiplied lung deposits, and levels are raised in some human tumors.
- Pregnancy or breastfeeding
- TrialExcluded from the ulcer and eye trials, so no human safety data cover it.
- Anyone injecting it under the skin
- PrecautionThat route has never been studied in people; the human data are IV infusions, eye drops and skin gel.
- People with diabetes
- TrialThe venous leg ulcer trial excluded diabetes, so the gel was never tested in people who have it.
- An eye infection or inflammation, with drops
- TrialThe dry-eye trials excluded active eye infection or inflammation needing treatment, and laser eye surgery in the previous six months.
- Anyone relying on product quality
- PrecautionNot approved anywhere, and vials sold as thymosin beta-4 or TB-500 may hold either molecule, which FDA treats as different substances.
Interactions
No interaction studies have been published, and no product label lists any. The ulcer and eye trials excluded people taking systemic steroids, immune-suppressing drugs or cancer chemotherapy, so those combinations are untested.
Trial: seen in human studies, or a group those studies left out. Precaution: follows from how it works or from a related drug, and hasn’t been tested. This isn’t a complete list: a pharmacist or doctor can check a specific medicine or condition.
Tracking and pairing
Worth tracking
- Injection-site reactions
- Any new lump or growth
- Eye pain, redness or vision changes (eye drops)
Often paired with
- BPC-157
Paired the same way as TB-500 for injuries. Never tested together.
Human studies
5 key published human studies, with how many people took part. Animal studies aren’t listed here.
-
In neurotrophic keratopathy, the corneal sore healed in 6 of 10 treated vs 1 of 8 on placebo at day 29 (p=0.066) and significantly more by day 43 (p=0.036), with no significant side effects.
- Design
- Randomized double-masked placebo-controlled Phase 3 trial (SEER-1), stopped early for business reasons
- Dose
- 0.1% eye drops (RGN-259) 5× daily
- Length
- 28 days, plus 2 weeks follow-up
Sosne et al., Int J Mol Sci 2022, PMID 36613994
-
In dry eye, corneal staining (change −0.41 vs −0.46) and discomfort (−0.4 vs −0.4) improved no more than on placebo; no serious adverse events.
- Design
- Randomized double-masked placebo-controlled Phase 3 trial (ARISE-3)
- Dose
- RGN-259 eye drops 4× daily
- Length
- 14 days
ReGenTree, posted registry results, NCT03937882
-
Heart scar size didn’t differ between groups overall, but treated patients whose first dose came within 8 hours of PCI (43 people) had significantly smaller scars than the placebo group.
- Design
- Randomized double-blind placebo-controlled trial of recombinant thymosin beta-4 after heart attack
- Dose
- IV after the artery-opening procedure (PCI); dose not given in the abstract
- Length
- 90-day follow-up
Zhang et al., Cardiovasc Res 2025, PMID 41229390
-
Adverse events were infrequent and mild to moderate, with no dose-limiting toxicity or serious events; exposure rose in proportion to dose and the half-life lengthened at higher doses.
- Design
- Randomized placebo-controlled dose-escalation Phase 1 trial in healthy volunteers
- Dose
- 42, 140, 420 or 1,260 mg IV
- Length
- Single dose, then daily for 14 days
Ruff et al., Ann N Y Acad Sci 2010, PMID 20536472
-
Safety was comparable to placebo; about 25% of ulcers closed within 3 months, mostly small to moderate ones, and 0.03% looked most promising. Registry results show 12 of 55 closed on gel vs 4 of 17 on placebo.
- Design
- Randomized double-blind placebo-controlled dose-escalation Phase 2 trial
- Dose
- 0.01%, 0.03% or 0.1% gel once daily on venous leg ulcers
- Length
- Up to 84 days
Guarnera et al., Ann N Y Acad Sci 2010, PMID 20536470
Limits of the evidence
In people: a 40-person IV safety trial over 14 days, two Phase 3 dry-eye trials in about 1,300 people that missed their main goals, gel trials in about 150 people with ulcers, and a 96-person heart attack trial in China. Injection under the skin, the route guides describe, has never been tested, and no trial followed anyone beyond a few months.
Mixing your vial
| Vial | Water | Common dose | Draw | Strength | Action |
|---|---|---|---|---|---|
| 5 mg | 1 mL | 2.5 mg | 50 units (0.50 mL) | 5 mg/mL | |
| 10 mg | 2 mL | 2.5 mg | 50 units (0.50 mL) | 5 mg/mL |
Mixed the same way as TB-500, but equal milligram doses aren’t equivalent: the full protein (about 4,963 g/mol) weighs about 5.6 times as much per molecule as the TB-500 fragment (889 g/mol), so 2.5 mg of it holds roughly one-sixth as many molecules as 2.5 mg of TB-500.
Dose chart
Syringe units for common doses at different water volumes. Select a cell to open it in the calculator.
| Dose | Water added | ||
|---|---|---|---|
| 1 mL | 2 mL | 3 mL | |
| 2 mg | |||
| 2.5 mg | |||
U-100 insulin syringe: 100 units is 1 mL. Draws over 100 units show in mL. Faded values are under 2 units, which is hard to measure. Check that your vial holds the larger volumes.
Datasheet
- Half-life
- No reliable value has been published.
- Type
- Peptide, 43 amino acids
- Molecular weight
- 4,963.5 g/mol
- Formula
- C212H350N56O78S
- Sequence
- Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGESN-terminal acetyl; residues 17–23, LKKTETQ, form TB-500
- Storage before use
- Freezer (about −20 °C) for long-term storage.
- After mixing or opening
- Fridge (2–8 °C); use within about 4 weeks.
- Molecule: PubChem CID 16132341 (timbetasin, CAS 77591-33-4, UNII 2D5MRE3SSY; PubChem rounds the weight to 4963); weight calculated from the formula
- Storage: Community Common practice; no approved label exists for this peptide
Every compound side by side: the half-life chart and the storage chart.
Cautions
- Not approved anywhere. Injection under the skin has never been studied in people; whole-body data come from short IV trials of 7–14 days.
- Benefit is unproven: the large dry-eye trials missed their main goals, and ulcers healed about as often on the gel as on placebo.
- Theoretical tumor concern: it helps cells migrate and grow new blood vessels, and high levels are found in some cancers.
- Vials sold as thymosin beta-4 or TB-500 may contain either molecule. Check the COA.
- Banned in sport at all times (WADA S2.3).
Questions
What is thymosin beta-4?
The full 43-amino-acid protein that nearly all cells make, also found in blood, tears and wound fluid; it binds actin, part of the cell’s internal skeleton, and helps cells move in to repair tissue. TB-500 is a 7-amino-acid piece of it (residues 17–23).
How does thymosin beta-4 work?
Thymosin beta-4 is the 43-amino-acid protein nearly all cells make. It binds G-actin, the free single units of a cell’s internal scaffolding, holding a pool cells draw on when they move; in animals it also speeds skin and eye healing and promotes new blood vessels. That mechanism rests on cell and animal work, while the human trials measured healing, not mechanism. Which of its actions matter in people is unknown, as is what it does over months: the whole-body human data are IV courses of up to 14 days.
Is thymosin beta-4 FDA-approved?
Not approved as a drug in the US or EU. Its eye drops (RGN-259) and a recombinant IV form are still in clinical trials. Not nominated for compounding: full-length thymosin beta-4 isn’t on FDA’s 503A category lists (updated May 14, 2026) or its 503B lists. The withdrawn nomination and the July 2026 advisory committee vote concern the TB-500 fragment, which FDA treats as a different substance.
What is the usual thymosin beta-4 dose?
From human studies (Ruff 2010): IV infusion of 42–1,260 mg once daily for 14 days in healthy volunteers, a safety test only. Eye drops: 0.1% solution (RGN-259) 5× daily for 28 days in neurotrophic keratitis; 2–6× daily for 2–4 weeks in dry-eye trials (SEER-1, 2023). These are the amounts sources reference, not recommendations.
How much water do I mix thymosin beta-4 with?
There’s no single right amount, because the water only sets the strength. With 1 mL of bacteriostatic water in a 5 mg vial, the strength is 5 mg/mL, so 2.5 mg is 50 units on a U-100 insulin syringe. More water makes small doses easier to measure. The dose chart above shows other volumes.
Who should avoid thymosin beta-4?
No product label covers thymosin beta-4, so these come from human studies and from precautions based on how it works. Anyone with active or past cancer: It drives cell migration and new blood vessels; forcing it up in mouse melanoma cells multiplied lung deposits, and levels are raised in some human tumors. Pregnancy or breastfeeding: Excluded from the ulcer and eye trials, so no human safety data cover it. Anyone injecting it under the skin: That route has never been studied in people; the human data are IV infusions, eye drops and skin gel. The “Who should avoid it” section lists 3 more groups.
How should thymosin beta-4 be stored?
Before mixing: Freezer (about −20 °C) for long-term storage. After mixing: Fridge (2–8 °C); use within about 4 weeks. This is common practice; no product label covers it.
Is thymosin beta-4 banned in sport?
Yes. S2.3 growth factors and growth factor modulators: “thymosin-β4 and its derivatives e.g. TB-500” are named. Banned at all times.
Has thymosin beta-4 been studied in people?
Yes. The human studies section lists 5 published studies. The largest, from 2021, included 700 people. In dry eye, corneal staining (change −0.41 vs −0.46) and discomfort (−0.4 vs −0.4) improved no more than on placebo; no serious adverse events.
Sources
- Ruff et al., IV thymosin beta-4 in healthy volunteers, Phase 1 (Ann N Y Acad Sci 2010) PMID 20536472
- Sosne et al., RGN-259 eye drops in neurotrophic keratopathy, SEER-1 (Int J Mol Sci 2022) PMID 36613994
- ARISE-3 dry-eye trial, posted registry results (NCT03937882)
- RegeneRx letter to stockholders on the SEER-2 trial (September 1, 2026)
- FDA briefing document: TB-500-related bulk drug substances (July 2026)
For the protocol details
- Wang et al., recombinant thymosin beta-4 Phase 1 in healthy Chinese volunteers (J Cell Mol Med 2021) PMID 34346165
- Guarnera et al., thymosin beta-4 gel in venous ulcers (Ann N Y Acad Sci 2010) PMID 20536470
- Treadwell et al., thymosin beta-4 in dermal healing, with two Phase 2 ulcer trials (Ann N Y Acad Sci 2012) PMID 23050815
- Zhang et al., recombinant thymosin beta-4 after heart attack (Cardiovasc Res 2025) PMID 41229390
- ARISE-3 and venous ulcer trials, posted registry results (NCT03937882, NCT00832091)
For how it works, who should avoid it and the limits of the evidence
- Goldstein et al., thymosin beta-4 as an actin-sequestering protein that repairs injured tissue (Trends Mol Med 2005) PMID 16099219
- Cha et al., thymosin beta-4 in tumor metastasis and angiogenesis (J Natl Cancer Inst 2003) PMID 14625258
- ARISE-3 dry-eye trial and venous ulcer trial, posted registry records and results NCT03937882
- FDA briefing document for TB-500-related bulk drug substances (July 2026)
Doses tagged Community come from public dosing guides and user reports, checked against at least two of them. Those sites aren’t named here because many of them sell peptides or earn commissions on them.