Compound hub · TB-500
TB-500 side effects: what do the safety records show?
The FDA's briefing document (memo dated 15 May 2026) reports finding no human clinical studies of TB-500, no case reports in the published medical literature and no reports in its adverse event database through 26 March 2025, and it calls the safety risks in humans unknown. No published human adverse-event data for TB-500 appear in the other sources checked for this page on 14 October 2026. Trials of full-length thymosin beta-4, a different molecule from TB-500, are reported separately below, each with its size and limits.
Your immune system can react to some foreign proteins and peptides. That reflex is a big reason regulators ask for human safety data before any peptide reaches approval. It is also the reason this page exists: people search for TB-500 side effects, and the honest answer starts with what was and was not recorded.
This page is part of the TB-500 hub. It reports adverse events from named documents, trial records and papers, starting with the FDA's briefing document of 15 May 2026, and it says plainly when no human data were found. The page gives no advice. For what the compound is, read the TB-500 explainer.
Key facts
| Common name | TB-500 |
|---|---|
| Defined in two 2012 papers as | Ac-LKKTETQ, 7 amino acids (Ho et al., 2012; Esposito et al., 2012) |
| FDA adverse event database | No reports retrieved for TB-500 through 26 March 2025; the FDA notes such data have limits (FDA briefing document, memo dated 15 May 2026) |
| Human clinical studies identified by the FDA | None identified (FDA briefing document, memo dated 15 May 2026) |
| Registered TB-500 trial | NCT07487363, Phase 1/2, recruiting, no results posted (ClinicalTrials.gov, read 14 October 2026) |
| FDA staff position | Proposed not adding TB-500 to the 503A bulks list (memo dated 15 May 2026) |
| FDA advisory committee meeting | 23–24 July 2026; the FDA meeting page read on 14 October 2026 posts no vote result |
| Closest human safety records | Trials of full-length thymosin beta-4, a different molecule from TB-500, mostly in healthy volunteers (see the comparison table) |
| Australian status | Schedule 4 and Appendix D clause 5 (F2026L01327, read 14 October 2026) |
Evidence limits
What are the side effects of TB-500?
The sources checked report no human side effects of TB-500, because they identify no human study of it with results. The FDA's briefing document (memo dated 15 May 2026) reports that a search of its adverse event reporting database through 26 March 2025 retrieved no reports for TB-500 and that its literature search identified no cases, and it notes that such data have limits. A separate FDA complaint system for food, dietary supplements and cosmetics held two reports about a blended TB-500 and BPC-157 product, and the reports carry no safety assessment of either ingredient (same document). ClinicalTrials.gov lists one TB-500 trial, NCT07487363, with adverse events as its primary outcomes and no results posted on 14 October 2026.
A missing report is not a clean bill of health. The FDA notes that reporting to its database is voluntary, that a reported event may not be caused by the product, that it does not receive every report, and that it cannot reach a definite safety conclusion from that data (FDA briefing document, memo dated 15 May 2026). The Therapeutic Goods Administration (TGA), Australia's medicines regulator, says unapproved peptide products, with TB-500 among its named examples, have not been evaluated for safety, quality or effectiveness (TGA safety advisory, 13 April 2026).
The registered trial runs at a hospital in Shenzhen, China, with 80 people planned and an estimated primary completion in February 2027 (ClinicalTrials.gov record, last update posted 23 March 2026). The record shows the trial began on 5 February 2026, while the FDA's memo dated 15 May 2026 says it identified no human studies. Both statements are reported here as found, and this page does not reconcile them.
What are the risks of TB-500, according to the FDA?
The FDA's briefing document (memo dated 15 May 2026) raises these concerns about TB-500: no human safety data, a risk of immune reactions to peptides of this kind, possible clumping of peptide molecules (aggregation) with impurities, and inconsistent naming that hides which chemical form a product holds. The FDA concluded that 'potential safety risks associated with the use of these substances in humans are unknown'. It also did not identify animal toxicity, genetic-damage, reproductive or cancer-risk studies of either TB-500 form.
Immunogenicity is the tendency of a peptide to provoke an immune response. The FDA says responses can range from antibodies with no apparent clinical manifestations to 'life-threatening and catastrophic reactions', and that outcomes in patients are often unpredictable. It adds that it did not identify any clinical study of TB-500 immunogenicity or aggregation (FDA briefing document, memo dated 15 May 2026).
Naming is part of the safety case. The FDA says TB-500 is a common name, not a formal drug name, and that suppliers sell different salts and forms under it. The free base and its acetate salt count as different bulk substances, and several supplier sites use the free base's CAS registry number (885340-08-9) for the acetate (FDA briefing document, memo dated 15 May 2026). The TB-500 identity page explains the sequence that the 2012 papers define.
What happened at the FDA advisory meeting on TB-500 in July 2026?
FDA staff proposed against adding TB-500, as free base or acetate, to the 503A bulks list, the list of substances US pharmacies may use to compound medicines (FDA briefing document, memo dated 15 May 2026). The FDA meeting page lists TB-500 on the Pharmacy Compounding Advisory Committee's 23 July 2026 agenda. That page, read on 14 October 2026, posts no vote result, so this page reports no vote count. The briefing document says the FDA will not issue a final determination until the committee's input has been considered and all reviews are finalised.
The FDA's own meeting page lists TB-500 among the substances discussed and shows no vote result. This page reports no vote count because the FDA page it read carries none.
The process concerns United States pharmacy compounding rules. It creates no status for TB-500 in Australia, where the Poisons Standard entries described in the Australian peptide law hub apply.
What adverse events did human trials of thymosin beta-4 record?
Human trials of full-length thymosin beta-4, a different molecule from TB-500, are the closest published adverse-event records. In a 2021 Phase 1 trial of recombinant thymosin beta-4 in healthy Chinese volunteers, events were reported by 25 of 44 treated and 7 of 10 placebo participants in the first part (54 volunteers) and by 16 of 24 treated and 5 of 6 placebo participants in the second part (30 volunteers); the authors reported no serious adverse events, in a sponsor-run trial that gave no TB-500 (Wang et al., Journal of Cellular and Molecular Medicine, 2021). In a 2010 randomised placebo-controlled trial of four groups of 10 healthy volunteers given synthetic thymosin beta-4, the abstract reports adverse events that were infrequent and mild or moderate and no serious adverse events, in a small trial that gave no TB-500 and whose abstract gives no event counts (Ruff et al., Annals of the New York Academy of Sciences, 2010).
The table below sets out every human study checked for this page that reported adverse-event counts. The studies differ in molecule form, population and design, so the rows cannot be added together.
Acetylation, the added chemical tag on TB-500, changes a peptide's charge, size and affinity for water. The FDA makes this point about the untagged fragment LKKTETQ: its profile 'cannot be directly extrapolated' to TB-500 (FDA briefing document, memo dated 15 May 2026). No row below is a TB-500 result.
Which side effects were listed in the first recombinant thymosin beta-4 trial?
In the first part of the 2021 Phase 1 trial of recombinant thymosin beta-4 (54 healthy Chinese volunteers: 44 treated, 10 placebo), the treated group's 45 recorded events included abnormal blood chemistry and blood counts (9 each), a raised squamous cell carcinoma tumour marker (8), abnormal urine tests (7) and abnormal ECGs (3); the authors reported all events as mild or moderate and none serious, and the placebo group logged the same kinds of events, so the counts do not show which events the product caused (Wang et al., Journal of Cellular and Molecular Medicine, 2021). In its second part (30 healthy volunteers: 24 treated, 6 placebo), the treated group's events included abnormal urine tests (8), abnormal ECGs (8, against 5 in the placebo group), raised triglycerides (3) and, in one person each, brief loss of vision, bruising at a puncture site and a slow heart rate, all within small cohorts of healthy adults in a trial of a different molecule from TB-500 (Wang et al., 2021).
In the second part of the 2021 Phase 1 trial of recombinant thymosin beta-4 (30 healthy volunteers: 24 treated, 6 placebo), one placebo participant and one treated participant in the highest cohort left the trial because of an abnormal ECG, two withdrawals in a small trial of a different molecule from TB-500 that do not establish a cause (Wang et al., 2021). In the 84 healthy volunteers of that trial, the authors saw a brief rise in the tumour marker that returned to normal after follow-up, linked it to epithelial cell regeneration, and reported finding no tumour-related adverse events over 28 days of follow-up, in a trial of a different molecule from TB-500 (Wang et al., 2021). In that trial, one of 108 antibody samples (from 54 volunteers) was positive in the first part, and two of 56 samples (from 28 volunteers) in the second part; every positive sample turned negative at follow-up in healthy adults given a different molecule from TB-500 (Wang et al., 2021).
Limits sit in the paper itself. The product was a 44-amino-acid recombinant version, the study was sponsored by its maker, and three authors are employees of the sponsor. All volunteers were healthy Chinese adults, so the trial reports nothing about other groups or about TB-500.
What is the half-life of TB-500 and thymosin beta-4?
The FDA's briefing document (memo dated 15 May 2026) reports finding no human pharmacokinetic study of TB-500 by any route, so it gives no human half-life. In a 2012 study of horses treated with one TB-500 product, plasma levels peaked at 60 to 120 minutes and fell below measurable levels by 6 to 10 hours, a time course in one animal species (number not stated in the FDA summary) that is not a half-life and does not describe people (Ho et al., Journal of Chromatography A, 2012, as summarised by the FDA). In the first part of a 2021 trial of 54 healthy volunteers, full-length recombinant thymosin beta-4 had half-lives of 0.5 to 2.08 hours across the six cohorts with pharmacokinetic sampling, in a different molecule from TB-500 and a sponsor-run trial of healthy adults (Wang et al., 2021).
A half-life is the time for a blood level to fall by half. In four groups of 10 healthy volunteers given a synthetic full-length thymosin beta-4, the 2010 trial abstract reports that half-life rose as the amount given rose and that exposure was proportional to the amount, the trial did not test TB-500, and the abstract gives no single half-life value, so this page supplies none (Ruff et al., 2010).
Blood level is only part of the story. In urine from treated rats (number not stated in the abstract), the piece Ac-LKK was still detectable up to 72 hours, a detection window for a breakdown product in one species and not a clearance time (Rahaman et al., Journal of Chromatography B, 2024). The horse figures also describe an animal and a veterinary product, not any human study.
Is there a cancer concern with thymosin beta-4 or TB-500?
Sport Integrity Australia states there is 'serious concern' that thymosin beta-4 increases the spread and growth of cancer cells, and that its safety profile remains largely unknown (Sport Integrity Australia, page read 14 October 2026). Two laboratory papers point in different directions, and neither involved TB-500. In a computer analysis of liver cancer records from a public database and in cultured liver cancer cell lines (sample numbers not given in the abstract), the thymosin beta-4 gene was highly expressed in liver cancer samples, and raising it in the cells increased viability, migration and invasion, a result that does not show an effect in people (Tang et al., Discover Oncology, 2024). In one mouse model of lung fibrosis with lung cancer (number of mice not given in the abstract), added recombinant thymosin beta-4 inhibited tumour growth, a result in one animal model that does not show an effect in people (Yu et al., International Journal of Molecular Sciences, 2023).
The FDA did not identify any carcinogenicity study of either TB-500 form (FDA briefing document, memo dated 15 May 2026), and no cancer study of TB-500 itself appeared in the sources opened for this page on 14 October 2026. The authors of the 2021 Phase 1 trial of recombinant thymosin beta-4 noted both signals in the literature and reported finding no tumour-related adverse events in their 84 healthy volunteers, who were followed for 28 days, in a trial of a different molecule from TB-500 (Wang et al., 2021).
Trial eligibility lists mention cancer. The registered TB-500 trial lists active malignancy requiring systemic therapy within the past two years among its exclusion criteria (NCT07487363), and the venous ulcer trial lists current or former malignancy among its exclusion criteria (NCT00832091).
What do 2026 reviews say about human safety data for TB-500?
Two 2026 reviews describe the human evidence as thin. A narrative review in Sports Medicine covered thymosin beta-4 and TB-500 among 12 peptides and concluded that many unapproved peptides show favourable tissue-repair results in animal models, but rigorous human safety data are scarce, with potential for serious harm; it is a review and not a trial, and only its abstract was checked (Mendias and Awan, 2026). A scoping review in The American Journal of Sports Medicine searched PubMed for six peptides including TB-500 and found that 67% of identified publications used animal models and that human clinical studies were limited to a handful of investigations, most lacking robust controls; only its abstract was checked (Tewari et al., 2026).
Neither abstract ties a specific adverse event to TB-500. The scoping review names congestive heart failure as a risk associated with another peptide in its group, MK-677, and lists cardiovascular and metabolic risks in general terms without saying which of its six peptides carried them (Tewari et al., 2026).
Does product quality add to the risk of unapproved peptides?
The TGA's Chief Medical Advisor, Professor Robyn Langham, said the biggest risks with unapproved peptide products are not knowing what is in the vial, how much peptide it holds, whether it is sterile or whether it carries contaminants (TGA warning, 7 May 2026). The FDA makes a related point about TB-500: the public certificates of analysis it reviewed did not show tests for impurities, aggregates, microbiological quality or bacterial endotoxin (FDA briefing document, memo dated 15 May 2026). Both statements concern missing product information, not measured side effects in people.
The catalogue lists TB-500 reference material as laboratory stock and says Certificates of Analysis are available on request. A certificate for one lot does not describe another, and research material is not a medicine. The TB-500 research guide collects the published studies behind the catalogue entry.
Comparison
Human studies of full-length or recombinant thymosin beta-4 that reported adverse-event counts, as published or posted by the sponsors. None tested TB-500. Each result cell names its main limit and source. Rows are not pooled.
| Study | Who | Adverse events recorded, main limit and source |
|---|---|---|
| Phase 1, healthy adults | 84 healthy Chinese adults (54 in the first part, 30 in the second); followed for 28 days | In 84 healthy Chinese adults given recombinant thymosin beta-4 or placebo, the authors reported no serious adverse events and described all events as mild or moderate, mostly laboratory, ECG and urine findings, with equal incidence and severity in treated and placebo groups (events in 25 of 44 treated and 7 of 10 placebo participants in the first part; 16 of 24 and 5 of 6 in the second); sponsor-run, healthy adults only, recombinant product, not TB-500 (Wang et al., 2021) |
| Safety study, healthy adults | 40 healthy adults in four groups of 10 | In four groups of 10 healthy volunteers given synthetic thymosin beta-4 or placebo, the abstract reports events that were infrequent and mild or moderate and no serious adverse events; the abstract gives no event counts; synthetic product, not TB-500 (Ruff et al., 2010) |
| Venous leg ulcers, Phase 2 | 72 people on the trial record (55 treated, 17 placebo; the paper reports 73 randomised); wound outcome assessed through day 84, adverse events collected for 99 days | In 72 people with venous leg ulcers (55 treated, 17 placebo), the trial record NCT00832091 lists participants reporting serious adverse events (3 of 55 treated, 1 of 17 placebo) and, among common non-serious events, participants reporting inflammation (4 treated, 1 placebo), itching (4 and 1), redness (3 and 0), upper respiratory infection (3 and 0) and urinary tract infection (3 and 0); these are counts of participants, not of events, over 99 days of collection; small groups, not TB-500 (NCT00832091; Guarnera et al., 2010) |
| Pressure ulcers, Phase 2 | 72 people enrolled (54 treated, 18 placebo started); wound outcome assessed through day 84, adverse events collected for 99 days | In people with pressure ulcers, the 99-day safety dataset of trial record NCT00382174 contains 53 treated and 18 placebo participants, and the record lists participants reporting serious adverse events (13 of 53 treated, 5 of 18 placebo) and non-serious events (40 of 53 treated, 13 of 18 placebo); trial-record counts only, no paper cited, not TB-500 (NCT00382174) |
| Epidermolysis bullosa, Phase 2 | 30 people (22 treated, 8 placebo); wound outcome at day 56, adverse events collected within 70 days; ended early | In 30 people with epidermolysis bullosa (22 treated, 8 placebo), the trial record NCT00311766 lists one participant with an event (cellulitis, a skin infection) in the treated group and 0 serious adverse events in either group over 70 days; ended early for lack of patients and expired study drug, so very small; a trial of full-length thymosin beta-4, not TB-500 (NCT00311766) |
| Dry eye, Phase 3 ARISE-3 | 700 people enrolled; about 4 weeks of adverse-event collection | In the dry-eye safety population of 699 people (350 treated, 349 placebo; about 4 weeks of adverse-event collection), the trial record NCT03937882 lists 0 serious adverse events in either group; the most frequent events, counted as participants reporting, were instillation-site pain (23 treated, 16 placebo), reduced visual acuity (12 and 7) and nasopharyngitis (7 and 6); trial-record counts only, a different molecule from TB-500 (NCT03937882) |
FAQ
Has TB-500 been tested for safety in humans?
The FDA's briefing document (memo dated 15 May 2026) says it identified no clinical studies or human exposure data for TB-500. ClinicalTrials.gov lists one recruiting Phase 1/2 trial, NCT07487363, whose primary outcomes are adverse events and which had posted no results on 14 October 2026.
Is thymosin alpha-1 the same peptide as TB-500?
No. Thymosin alpha-1 and thymosin beta-4 are separate thymus peptides: in superfused hypothalami from female rats (number not stated in the abstract), Rebar et al. found that thymosin beta-4, but not thymosin alpha-1, stimulated release of luteinizing hormone-releasing factor, a laboratory result that does not describe people (Science, 1981). TB-500 is a 7-amino-acid fragment of thymosin beta-4. This page does not review the safety record of thymosin alpha-1.
Has the FDA approved TB-500?
The FDA's briefing document (memo dated 15 May 2026) states that TB-500 is not a component of an FDA-approved drug and has no United States Pharmacopeia monograph. The TGA advisory of 13 April 2026 names TB-500 among unapproved peptide products that the TGA has not evaluated for safety, quality or effectiveness.
Where do online lists of TB-500 side effects come from?
The FDA's briefing document (memo dated 15 May 2026) reports finding websites that discuss and sell TB-500, and no published human case reports and no clinical studies of TB-500. This page did not review individual website lists, so it cannot say what any list is based on.
More in this hub
Citations
11 sourcesWang X et al. Journal of Cellular and Molecular Medicine. 2021;25(17):8222-8228.
doi:10.1111/jcmm.16693Ruff D et al. Annals of the New York Academy of Sciences. 2010;1194:223-229.
doi:10.1111/j.1749-6632.2010.05474.xGuarnera G et al. Annals of the New York Academy of Sciences. 2010;1194:207-212.
doi:10.1111/j.1749-6632.2010.05490.xHo EN et al. Journal of Chromatography A. 2012;1265:57-69.
doi:10.1016/j.chroma.2012.09.043Esposito S et al. Drug Testing and Analysis. 2012;4(9):733-738.
doi:10.1002/dta.1402Rahaman KA et al. Journal of Chromatography B. 2024;1235:124033.
doi:10.1016/j.jchromb.2024.124033Tang L et al. Discover Oncology. 2024;15:671.
doi:10.1007/s12672-024-01558-0Yu R et al. International Journal of Molecular Sciences. 2023;24(4):3818.
doi:10.3390/ijms24043818Mendias CL, Awan TM. Sports Medicine. 2026;56:1921-1935.
doi:10.1007/s40279-026-02437-0Tewari K et al. The American Journal of Sports Medicine. 2026, online 11 August.
doi:10.1177/03635465261464420Rebar RW et al. Science. 1981;214:669-671.
doi:10.1126/science.7027442
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TB-500 reference materialResearch use only — not for human or animal use.
Read the TB-500 research guideForm Laboratories supplies research-use-only reference material. This article is an educational summary of published third-party literature. It is not medical advice, not a use instruction, and research material is not for human or animal use.