The answer so far
Some human trials have studied eye drops containing full-length thymosin beta-4. Their results are mixed, and a large dry-eye trial did not meet its main endpoints. These were eye-drop studies of a different molecule, not trials of TB-500 for tendon or muscle recovery.123456
On this page
Why are eye studies cited in discussions of injury?
Thymosin beta-4 occurs naturally in the body and has been studied in processes associated with cell movement and tissue repair. Researchers developed RGN-259, an investigational sterile eye solution containing the full-length molecule, to study conditions affecting the eye’s surface. The nominated TB-500 fragment described by the FDA is a different, chemically modified shorter molecule. A related name does not make the two products interchangeable. See how the molecules differ. Thymosin alpha-1 is another, distinct peptide; see the name comparison.61
What did the first 72-person trial find?
In a 2015 masked, placebo-controlled dry-eye trial, 72 adults were assigned the investigational drops or matching inactive drops. Researchers measured discomfort and used a dye to assess changes on the transparent front surface of the eye, the cornea. Neither of the two main measures differed significantly at the prespecified assessment. Some other, secondary measurements favoured the active drops. These signals may inform future research, but they do not erase the main result or prove repair of other tissues.1
What did the larger ARISE-2 study report?
ARISE-2 enrolled 601 people with dry eye. In the sponsor-submitted registry results checked on 5 November 2026, the reported average changes for the day-29 discomfort response and a staining measure did not favour RGN-259 over placebo. The staining result covered selected subgroups of 111 and 107 people, rather than everyone in the study. The registry entry did not provide a formal statistical test comparing the groups for those posted primary results. These details matter when comparing claims about the trial.2
What happened in ARISE-3?
ARISE-3 enrolled 700 people; its reported main analysis counted 351 in the RGN-259 group and 348 in the placebo group, because one participant was enrolled twice. After 14 days, the average day-15 discomfort score change was −0.4 points in each group on a 0–5 scale, where higher scores meant worse discomfort. The sponsor reported that the main endpoints were not met, while a secondary measure of grittiness favoured the drops. A secondary finding is worth reporting, but it is not the same as success on the main question.34
- 2015 · 72 peopleDry eye: neither main measure differed significantly; some secondary measures favoured the drops.
- ARISE-2 · 601 enrolledDry eye: posted day-29 primary results did not favour the drops; one measure used a selected subgroup.
- ARISE-3 · 700 enrolledDry eye: the sponsor reported that the main endpoints were not met; a secondary symptom favoured the drops.
- SEER-1 · 18 peopleDifferent eye condition: 6 of 10 versus 1 of 8 had healed at the main assessment; the study was small.
What about a study of a different eye condition?
A separate small trial investigated neurotrophic keratopathy: damage to nerves supplying the cornea that can leave a persistent surface defect. At the main assessment after four weeks, complete healing was reported in 6 of 10 people receiving RGN-259 and 1 of 8 receiving placebo; the reported comparison did not reach the usual statistical threshold. The study was small and stopped early because recruitment was slow; it was funded by the developer, and some authors were company employees. It provides a reason for further investigation, not a reliable estimate of effect for dry eye, another product or an injury elsewhere.5
What do these findings mean for TB-500 and injuries?
The eye trials used a defined eye-drop preparation of the longer molecule for eye conditions; they did not test a TB-500 vial for tendon, ligament or muscle recovery. In its July 2026 review, the FDA said it had identified no clinical studies or human exposure data for its nominated TB-500 fragment. That describes its search, not proof that nobody has used a product bearing the name. Learn how TB-500 and BPC-157 injury claims compare.16
How should I use this information?
If a claim mentions a human trial, look for the molecule, formulation, condition, comparison and the outcome measured. A result on eye discomfort is not a tendon-healing result; a negative main endpoint in one setting is not proof that every related molecule is ineffective. For ongoing eye symptoms or an injury, a qualified clinician can assess the actual problem. Return to the TB-500 overview.35
Sources, kept close.
Selected supporting sources; this is not a complete literature review.
- Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trialClinical Ophthalmology / PubMed · Randomised placebo-controlled trial of full-length thymosin beta-4 eye solution; United States; 2015
- ARISE-2: RGN-259 ophthalmic solution for dry eye (NCT02974907)ClinicalTrials.gov / U.S. National Library of Medicine · Sponsor-submitted randomised trial and registry results
- ARISE-3: RGN-259 ophthalmic solution for dry eye (NCT03937882)ClinicalTrials.gov / U.S. National Library of Medicine · Sponsor-submitted randomised trial and registry results
- RegeneRx reports topline results of ARISE-3 dry eye trialRegeneRx Biopharmaceuticals · 2021 sponsor press release
- RGN-259 ophthalmic solution for neurotrophic keratopathy: randomized placebo-controlled phase III trialInternational Journal of Molecular Sciences / PubMed Central · 2023 primary clinical trial report
- FDA briefing on TB-500-related bulk drug substancesU.S. Food and Drug Administration · Advisory committee briefing; United States; July 2026