TB-500 Side Effects: What Safety Research Has Found
TB-500 side effects have been studied across preclinical animal models and, indirectly, through human trials of the parent molecule thymosin beta-4. This guide reports what those studies observed, what the FDA flagged, and what remains genuinely unknown.
What Is TB-500, and How Did Scientists Think About Its Safety?
Here is a curious fact: thymosin beta-4, the natural protein that TB-500 is based on, is produced by almost every cell in the human body. It is released in large quantities whenever tissue is damaged. Scientists studying TB-500 side effects were not looking at a foreign chemical compound, but at a synthetic copy of a fragment the body already makes constantly. That context shapes everything about how the safety research was designed and what it found.
TB-500 is the lab-made version of the LKKTETQ sequence, a seven-amino-acid stretch within thymosin beta-4 that researchers identified as the most biologically active region. Amino acids are the small building blocks that cells use to make proteins. A seven-amino-acid chain is unusually short, more like a molecular key than a full lock mechanism. That brevity is partly why scientists expected its safety profile to be favorable, and largely why the published data on the parent molecule is consistent with that expectation, with one important exception the FDA would later articulate.
That last number matters enormously. Most of what researchers know about TB-500 side effects comes from studies of the full-length thymosin beta-4 molecule, not the LKKTETQ fragment specifically. The fragment and the full protein share the actin-binding region, but the full protein has additional structural domains that behave differently. Readers should hold this distinction in mind throughout this guide.
Regulatory and Approval Status
TB-500 has no FDA approval for any human or veterinary application. On September 29, 2023, the FDA placed TB-500 (Thymosin beta-4, Fragment, LKKTETQ) on the Section 503A Category 2 bulk drug substance list, meaning licensed compounding pharmacies are currently prohibited from preparing injectable TB-500 for human use. The FDA’s stated rationale centered on immunogenicity concerns and the absence of human exposure data for the fragment specifically. Thymosin beta-4 and its derivatives, including TB-500, are also prohibited at all times under the 2026 WADA Prohibited List within Section S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics). (FDA 503A Category 2 List; WADA 2026 Prohibited List)
What Preclinical Safety Studies Observed About TB-500
Preclinical safety studies, meaning experiments in animals before any human use, consistently found a favorable safety profile for thymosin beta-4 across multiple species, routes, and dosing regimens. The data summarized below describes full Tβ4 unless explicitly noted; dedicated controlled toxicology studies of the LKKTETQ fragment specifically remain limited.
No Toxicology Identified Across Multiple Species
A comprehensive review of thymosin beta-4 safety across animal models, spanning mice, rats, pigs, and dogs, arrived at a direct conclusion: the safety profile is excellent, and no preclinical toxicology has been identified. This statement covers experiments using subcutaneous injection (just under the skin), topical application, intraperitoneal injection (into the abdominal cavity), and intravenous administration. The absence of toxicological findings across four different species and multiple routes is a meaningful data point in preclinical safety assessment, though it does not replace human clinical data and was generated using full-length Tβ4 rather than the LKKTETQ fragment. (Crockford et al., Ann N Y Acad Sci. 2010. PMID: 20536453)
No Tumorigenesis in Large-Animal Cardiac Model
A 2021 study published in Theranostics examined co-treatment with thymosin beta-4 microspheres and lab-grown heart cells (hiPSC-derived cardiomyocytes, meaning heart muscle cells grown from human stem cells in a lab) in immunosuppressed pigs following an induced heart attack. Researchers conducted whole-body MRI evaluation and found no tumorigenesis (no abnormal tissue growth or tumors) in any treated animal. This finding addressed a theoretical concern: because Tβ4 promotes angiogenesis (the growth of new blood vessels), some researchers had asked whether that effect could feed pre-existing abnormal growth. In this large-animal model, no such effect was observed within the study timeframe. (Cheng et al., Theranostics. 2021. PMID: 34267750)
No Increase in Cardiac Arrhythmia
The same porcine model found no increase in ventricular arrhythmia with thymosin beta-4 treatment. This was specifically noted by researchers as important, given that the compound promotes cardiomyocyte (heart cell) proliferation and new vessel formation, both of which could theoretically disrupt the electrical signaling patterns that regulate heartbeat rhythm. No such disruption was detected at the dose and duration used in this model. (Cheng et al., Theranostics. 2021. PMID: 34267750)
Pharmacokinetics and Clearance
In preclinical models of full-length thymosin beta-4, plasma half-life (the time it takes for half the compound to clear the body) has been reported in the range of a few hours following parenteral administration, consistent with how the body handles small, soluble peptides through renal filtration and peptidase activity. The pharmacokinetics of the LKKTETQ fragment specifically have not been characterized as thoroughly in the published literature, and shorter peptides are generally expected to clear more rapidly than the full 43-amino-acid protein. A Phase I human trial of full recombinant Tβ4 reported no apparent drug accumulation with continuous administration across 84 subjects, a relevant signal for the parent molecule even though it does not directly establish fragment pharmacokinetics. (Wang et al., J Cell Mol Med. 2021. PMID: 34000060)
What Human Clinical Trials Recorded About Thymosin Beta-4 Safety
Human clinical safety data exists for the full-length thymosin beta-4 protein, not for the TB-500 fragment specifically. This is a critical distinction. The data below describes what researchers observed with recombinant Tβ4, a pharmaceutical-grade version of the full 43-amino-acid protein produced under GMP (Good Manufacturing Practice) conditions. TB-500, as a research compound, is the LKKTETQ fragment and lacks the same manufacturing controls and clinical safety record.
Phase I Intravenous Safety Trial (84 Subjects)
In a Phase I intravenous safety trial published in the Journal of Cellular and Molecular Medicine in 2021, researchers enrolled 84 healthy subjects across multiple dose cohorts of recombinant thymosin beta-4 administered intravenously (directly into a vein, the most bioavailable route). The study reported no dose-limiting toxicities and no serious adverse events across any dose cohort. Researchers also confirmed no obvious drug accumulation with continuous administration, a key safety signal researchers look for in peptide compounds. Intravenous administration is more demanding than subcutaneous injection, so clean safety results by this route are considered informative for lower-exposure routes within the same compound class. (Wang et al., J Cell Mol Med. 2021. PMID: 34000060)
Phase II Dry Eye Trials (No Adverse Events Reported)
RegeneRx Biopharmaceuticals conducted two randomized controlled trials of topical thymosin beta-4 eye drops (0.1% concentration, applied 6 times per day) in patients with severe dry eye disease. A physician-sponsored trial enrolled 9 subjects (18 eyes) and a larger multicenter trial enrolled 72 subjects randomized 1:1 to Tβ4 or placebo. Both trials reported no adverse events attributable to study drug in either the treatment or placebo groups. The clean safety profile in these ophthalmic trials is notable because topical ocular administration has direct mucosal contact, a route where irritation or immune reactions are common with many compounds. (Sosne et al., Invest Ophthalmol Vis Sci. 2013. PMID: 23869074)
Phase 2 Cardiac Trial (90 STEMI Patients)
A multicenter Phase 2 randomized double-blind trial of thymosin beta-4 (designated NL005) enrolled 90 patients who had experienced STEMI (a serious heart attack involving complete blockage of a major coronary artery) and had undergone PCI (percutaneous coronary intervention, a procedure to open the blocked artery). The trial evaluated cardiac outcomes at days 5 and 90 following treatment. The safety profile was described as well-tolerated across the study population, with intravenous Tβ4 administration in an acute cardiac setting producing no notable safety signals reported by the investigators. This represents the highest-risk clinical population yet studied for full Tβ4 safety. (ClinicalTrials.gov NCT05485818; NCT05984134)
Research Insight: Why the Fragment Distinction Matters for Safety
- Every human clinical trial cited in this guide used pharmaceutical-grade, full-length recombinant thymosin beta-4, not the TB-500 fragment. The fragment lacks the Ac-SDKP domain (the first four amino acids of Tβ4) which may contribute independent anti-fibrotic and cardiovascular-protective effects.
- TB-500 as a research compound is produced without GMP pharmaceutical manufacturing controls, meaning purity, aggregation state, counterion content, and impurity profile can vary significantly between suppliers.
- The FDA’s concern about TB-500 side effects is specifically about compounded preparations of the LKKTETQ fragment, not about full Tβ4 as evaluated in clinical trials.
- The three populations studied with full Tβ4 (healthy IV-dosed volunteers, dry-eye patients, post-STEMI cardiac patients) are not interchangeable safety cohorts. Each program tells you something different about a different administration context.
See the analytical specifications and Certificate of Analysis for Phoenix Peptide Labs TB-500 →
The FDA’s Stated Concern About TB-500 Side Effects
The FDA’s September 2023 decision to list TB-500 on the Section 503A Category 2 bulk drug substances list was accompanied by a specific public rationale, and understanding it precisely is essential to reading the safety picture accurately.
What the FDA Actually Said
The FDA’s verbatim statement on TB-500 reads: “Compounded drugs containing thymosin Beta-4, Fragment (LKKTETQ) may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities. FDA has not identified any human exposure data for drug products containing Thymosin Beta-4, Fragment. FDA lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans.” (FDA 503A Category 2 Bulk Drug Substance List, 2023)
This statement contains two distinct concerns, and they are worth separating. The first is about the compound itself: small peptides can aggregate (clump together into larger structures) under certain manufacturing or storage conditions, and aggregated peptides are more likely to trigger an immune response (immunogenicity means “the ability to provoke an immune reaction”). The second is about the data gap: the FDA has no human exposure data for TB-500 the fragment, as opposed to the full Tβ4 protein.
What the FDA Concern Is Not
The FDA concern is explicitly about compounded preparations of the LKKTETQ fragment, not about the full-length recombinant Tβ4 protein used in clinical trials. The clinical-grade Tβ4 evaluated by RegeneRx (RGN-259, NL005) is a molecularly distinct compound produced under pharmaceutical GMP standards with full purity characterization, and it is evaluated under an IND (Investigational New Drug) application with clinical safety data. The FDA restriction does not apply to that pathway. The concern is specifically about injectable TB-500 produced by compounding pharmacies without the GMP controls that clinical-trial-grade Tβ4 carries. (FDA 503A Category 2 reference)
The Immunogenicity Risk in Plain Words
Immunogenicity means “the ability to provoke an immune reaction.” For injected peptides, the primary risk often comes not from the compound itself but from impurities in non-pharmaceutical-grade preparations:
- Peptide aggregates: Clumped peptide chains look foreign to the immune system and can trigger antibody responses ranging from mild to severe.
- TFA residuals: Trifluoroacetic acid (TFA) is commonly used in peptide synthesis and purification; residual amounts can be irritating or immunogenic when injected.
- Sequence variants: Non-GMP synthesis can produce slightly incorrect amino acid sequences that behave unpredictably in biological systems.
- Endotoxins: Bacterial contamination byproducts that can cause fever, inflammation, and in high doses, systemic immune reactions.
What TB-500 Side Effects Research Can’t Tell Us Yet
No body of research tells the complete story. Here are the most important gaps in what the current TB-500 safety literature can answer.
- Because no human study has used TB-500 the fragment specifically, we can’t yet say what adverse effects, if any, TB-500 (LKKTETQ) produces in humans at any dose or route.
- Because all clean human safety data comes from full-length Tβ4, we can’t yet say whether the fragment behaves identically to the full protein in immune, renal, or hepatic systems.
- Because the long-term effects of repeated administration have not been studied in any species, we can’t yet say what TB-500’s safety profile looks like beyond the typical preclinical and short clinical study windows.
- Because no study has specifically tested the angiogenesis-oncology interaction for the LKKTETQ fragment, we can’t yet confirm or rule out whether the fragment’s pro-angiogenic effects are relevant in the context of pre-existing abnormal tissue.
- Because research-grade TB-500 lacks standardized manufacturing controls, we can’t yet generalize safety data from GMP-grade Tβ4 trials to uncharacterized research-chemical TB-500 preparations.
Issue: Preclinical safety data exists for full Tβ4, not the LKKTETQ fragment specifically. Research Gap: No published study has evaluated the immunogenicity of TB-500 specifically in any animal model in a controlled toxicology framework.
Issue: TB-500’s pro-fibrotic paradox. Research Gap: The full Tβ4 molecule contains the Ac-SDKP domain, which actively suppresses the TGF-beta1/Smad fibrogenic pathway. TB-500 lacks this domain entirely. Whether this absence produces a meaningfully different anti-fibrotic profile has not been studied in a head-to-head comparison.
The following findings come from named, cited studies. Each is described with its model type, what researchers observed, and the appropriate caveat. Most relate to full-length Tβ4 rather than the LKKTETQ fragment specifically.
How to Make Sense of TB-500 Side Effects Research
Reading peptide safety research accurately requires understanding a few key concepts that change how any individual study should be interpreted.
Factor 1: Fragment vs. Full Molecule
TB-500 is a seven-amino-acid fragment of a 43-amino-acid protein. The full protein has at least four distinct functional regions. TB-500 contains only the actin-binding domain (residues 17 to 23). The remaining regions, including the Ac-SDKP anti-fibrotic domain and the N-terminal cytoprotective region, are absent. This means safety data from full Tβ4 trials is relevant but not directly transferable to the fragment.
An analogy: a study showing that a full multi-vitamin is safe does not automatically establish that one isolated component at the same dose is safe in the same way, because the compound’s behavior in the body depends on its full structure.
Factor 2: GMP vs. Non-GMP Manufacturing
GMP stands for Good Manufacturing Practice: a set of quality standards enforced by the FDA for pharmaceutical production. Clinical-trial-grade Tβ4 is produced under GMP conditions with full purity characterization, sterility testing, and endotoxin limits. Research-grade TB-500 sold as a chemical research compound may not meet these standards. The FDA’s immunogenicity concern is largely a manufacturing concern, not a pharmacology concern.
When a safety finding from a GMP-manufactured clinical compound is applied to a non-GMP research compound, the researcher should be aware of that gap. A certificate of analysis (COA) from an accredited laboratory provides at least purity and identity verification.
Factor 3: Angiogenesis and Theoretical Oncology Risk
Angiogenesis means the growth of new blood vessels. Tβ4 and its fragments promote angiogenesis, which is central to the parent molecule’s tissue repair activity. The theoretical concern is that in a context where abnormal tissue is already growing, new blood vessels could supply that growth. This concern has been raised for multiple pro-angiogenic compounds in the research literature.
The 2021 porcine model found no tumorigenesis in immunosuppressed animals treated with Tβ4 within the study timeframe. This does not rule out the theoretical concern in all biological contexts, but it does represent one of the few experimental data points on the question. The concern remains theoretical and unconfirmed for TB-500 the fragment specifically in any model.
Want to explore the published science directly? Browse the Phoenix Peptide Labs research library →
Factor 4: The Pro-Fibrotic Paradox
Full thymosin beta-4 is anti-fibrotic, meaning it reduces scar tissue formation. This property comes primarily from the Ac-SDKP domain at the N-terminus of the full protein, which suppresses the TGF-beta1/Smad signaling pathway (a key driver of fibrosis, or scarring, in organs including the heart, liver, and kidneys). TB-500 lacks this domain entirely.
What This Means for Reading the Evidence
Research applications where fibrosis modulation is the area of interest may not be well-served by the LKKTETQ fragment alone. At the same time, the actin-binding domain present in TB-500 does have some anti-inflammatory properties through NF-kB pathway suppression, so the picture is not simply “fragment equals no anti-fibrotic effect” but rather “fragment has different anti-fibrotic coverage than the full molecule.” (Zuo et al., Front Pharmacol. 2022. PMC9434483)
Factor 5: The Absence of Evidence vs. Evidence of Absence
No published study has found serious adverse effects from TB-500. That is different from saying TB-500 has been proven safe. The preclinical data for full Tβ4 is genuinely favorable. The human data for the parent molecule is genuinely favorable. But the fragment has not been tested in humans, which means the absence of reported problems is partly a reflection of the absence of rigorous testing.
Scientists describe this distinction as “absence of evidence is not evidence of absence.” It means: not finding a problem is informative, but only up to the sensitivity and scope of the experiments that were run.
Factor 6: What a Certificate of Analysis Can and Cannot Tell You
A Certificate of Analysis (COA) from an accredited analytical laboratory confirms identity (that the compound is TB-500) and purity (that it meets a stated purity threshold, typically by HPLC). HPLC stands for high-performance liquid chromatography, a technique that separates and measures individual molecular components in a sample. A COA with HPLC purity confirmation addresses some of the FDA’s impurity concern, because it rules out gross contamination and sequence variants that HPLC can detect.
A standard HPLC purity panel does not confirm sterility, endotoxin levels, aggregation state, or residual solvent content. Those properties require additional analytical tests beyond purity alone, and they are the specific factors most relevant to immunogenicity risk with injected peptides. Researchers comparing supplier COAs should look at what testing was actually performed, not only at the reported purity number.
TB-500 Safety Data Across Research Models
The table below compiles safety-relevant findings from the published literature. Every finding is attributed to its source, model, and population. The distinction between TB-500 the fragment and full Tβ4 is indicated in each row.
| Study / Source | Compound | Model / Population | Route | Safety Finding | Limitation / Caveat |
|---|---|---|---|---|---|
| Crockford et al., 2010 (PMID: 20536453) | Thymosin beta-4 (full) | Mice, rats, pigs, dogs (multi-species preclinical) | Multiple | No preclinical toxicology identified; excellent safety profile | Animal data only; full Tβ4 molecule, not TB-500 fragment |
| Wang et al., 2021 (PMID: 34000060) | Recombinant Tβ4 (GMP) | 84 healthy human subjects, Phase I | Intravenous | No dose-limiting toxicities; no serious adverse events; no drug accumulation | GMP full Tβ4 only; small healthy-volunteer cohort; short duration |
| Sosne et al., 2013 (PMID: 23869074) | Tβ4 ophthalmic drops (RGN-259) | 9 subjects pilot + 72-subject RCT, dry eye | Topical ocular | No treatment-attributable adverse events in either trial | Topical mucosal route only; small-to-moderate sample sizes |
| ClinicalTrials.gov NCT05485818 | Tβ4 (NL005) | 90 STEMI patients, Phase 2 cardiac trial | Intravenous | Well-tolerated safety profile; no notable safety signals in acute cardiac population | GMP Tβ4; cardiac population with acute comorbidities; moderate sample size |
| Cheng et al., 2021 (PMID: 34267750) | Tβ4 microspheres | Immunosuppressed pigs, cardiac model | Local cardiac delivery | No tumorigenesis at whole-body MRI; no ventricular arrhythmia increase | Large-animal model; specialized cardiac delivery context; not representative of systemic injection |
| FDA, 2023 (503A Cat. 2) | TB-500 (LKKTETQ fragment) | Regulatory assessment; no human data reviewed | Injectable (concern) | Immunogenicity concern from aggregation and impurities; no human data identified | Regulatory determination, not a clinical study; applies to compounded preparations specifically |
| Zuo et al., 2022 (PMC: 9434483) | Tβ4 Ac-SDKP domain | Organ fibrosis models (review) | Various | Ac-SDKP specifically mediates anti-fibrotic effects; TB-500 fragment lacks this domain | Review article on full Tβ4 pathway; TB-500’s fibrosis profile not directly studied |
Where TB-500 Side Effects Research Shows Up
Three distinct research territories have produced the safety-relevant data on TB-500 and thymosin beta-4. Each has a different purpose and different implications for reading the safety picture.
FDA’s Manufacturing Quality Concern
The Finding: The FDA’s 2023 Category 2 determination for TB-500 did not cite pharmacological toxicity. It cited manufacturing quality: the risk that compounded injectable preparations of the LKKTETQ fragment may contain aggregates and impurities that create immunogenicity risk independent of what the active compound does.
The Open Question: At what purity threshold and aggregate level does an injected TB-500 preparation pose meaningful immunogenicity risk? No published study has established this threshold for the LKKTETQ fragment.
Takeaway: Analytical quality data, including HPLC purity, endotoxin testing, and aggregation assessment, is the most relevant safety-adjacent information available for research-grade TB-500 preparations.
Human Trials of the Parent Molecule
The Finding: Three human trial programs of full-length Tβ4, Phase I IV safety, Phase II ophthalmic, and Phase 2 cardiac, have collectively studied the parent molecule across three distinct populations using GMP-grade material. No serious adverse events were identified across these trials. This is the highest-quality safety signal available for the Tβ4 class.
The Open Question: How much of this safety record transfers to the TB-500 fragment in a non-GMP research-compound context? The fragment lacks portions of the molecule included in the clinical-grade preparations and is produced under different manufacturing conditions. The three populations studied are also not interchangeable safety cohorts.
Takeaway: The human safety record for full Tβ4 is genuinely favorable and relevant context, but it is not a direct safety certification for TB-500 the research compound.
Angiogenesis and the Oncology Question
The Finding: Tβ4 and the LKKTETQ region promote angiogenesis through VEGF pathway activation. This is a documented part of the mechanism of action in repair models. The porcine cardiac model found no tumorigenesis with Tβ4 treatment within the study timeframe. (Cheng et al., 2021)
The Open Question: Does pro-angiogenic activity from TB-500 the fragment present any meaningful risk in biological contexts involving pre-existing abnormal tissue growth? The existing animal data does not address this question in a targeted experimental design with the LKKTETQ fragment specifically.
Takeaway: The single available large-animal data point is reassuring but narrow. Researchers reading the literature should treat the angiogenesis-oncology question as open rather than answered, especially for the fragment.
Frequently Asked Questions About TB-500 Side Effects Research
These questions reflect common points of confusion in the published literature on TB-500 and thymosin beta-4. Answers are summarized from the sources cited throughout this guide.
There is no published peer-reviewed clinical research on TB-500 (the LKKTETQ fragment) side effects in humans. The FDA stated this explicitly in its 2023 Section 503A Category 2 determination: it could not identify any human exposure data for products containing the fragment specifically. Human safety data does exist for the full-length thymosin beta-4 molecule, which is a related but molecularly distinct compound. That data is favorable but does not directly answer the question for the fragment.
No. Thymosin beta-4 is a 43-amino-acid protein. TB-500 is a synthetic seven-amino-acid fragment (LKKTETQ) corresponding to residues 17 through 23 of the parent protein. They share the actin-binding region but the fragment lacks the Ac-SDKP anti-fibrotic domain, the N-terminal cytoprotective region, and other portions of the full molecule. Safety findings for one do not automatically transfer to the other. Most published clinical and preclinical data referenced in popular discussions of TB-500 actually used the full molecule.
The FDA’s September 2023 listing cited two issues. First, compounded preparations of the LKKTETQ fragment may aggregate or contain peptide-related impurities, both of which can provoke an immune response when injected. Second, the FDA could not identify any human exposure data for the fragment, meaning there is no clinical record to evaluate whether the compound would cause harm in humans. The concern is specifically about compounded injectable TB-500, not about full Tβ4 as evaluated under IND clinical trial programs.
No published study has demonstrated tumorigenesis from TB-500 or full thymosin beta-4. A 2021 porcine cardiac model found no tumors at whole-body MRI in immunosuppressed pigs treated with Tβ4. However, the angiogenesis-oncology concern remains theoretical rather than fully resolved, because no targeted study has evaluated the LKKTETQ fragment specifically in a context of pre-existing abnormal tissue growth. The available data is reassuring but narrow.
The FDA’s stated concerns map to specific analytical parameters that a comprehensive COA can address: peptide-related impurities (visible on HPLC), aggregation state (typically measured by size-exclusion chromatography), residual TFA from synthesis, residual solvents, water content, counterion content, and where applicable, endotoxin levels and sterility. A standard purity-only COA addresses some but not all of these. Researchers comparing supplier documentation should look at the full panel of tests performed, not only the purity percentage.
Direct comparisons across different research peptides are not particularly meaningful because the underlying study designs, models, doses, and routes vary widely. Both TB-500 and BPC-157 are listed on the FDA’s Section 503A Category 2 bulk drug substance list as of 2023 to 2024, with similar rationales around the absence of human exposure data and concerns about manufacturing quality in compounded preparations. Both are also prohibited under the WADA Prohibited List. Beyond regulatory parallels, head-to-head safety comparisons in the published literature are not available.
Pharmacokinetic data for the LKKTETQ fragment specifically is limited in the public literature. Full-length Tβ4 has reported plasma half-lives in the range of a few hours in preclinical models following parenteral administration. Short peptides like the LKKTETQ fragment are generally cleared more rapidly than larger proteins due to renal filtration and peptidase activity, but the precise pharmacokinetic profile of TB-500 has not been characterized as thoroughly as that of the parent molecule.
No. RegeneRx Biopharmaceuticals has conducted clinical trials using full-length recombinant thymosin beta-4, designated as RGN-259 (ophthalmic), RGN-352 (cardiac, also referred to as NL005), and related formulations. These are pharmaceutical-grade preparations of the entire 43-amino-acid protein, produced under GMP conditions and evaluated under FDA IND applications. TB-500 the LKKTETQ fragment is a different molecule produced through different routes and has not been the subject of those clinical programs.
Important Research Disclaimer. All compounds discussed on this site, including TB-500 (Thymosin beta-4, Fragment, LKKTETQ), are sold and offered as reference materials for research use only. They are not drugs, supplements, cosmetics, or food products. They are not intended for human ingestion, injection, inhalation, topical application, or any other in-vivo human or veterinary use. Sales are restricted to qualified researchers operating in appropriate laboratory environments.
TB-500 is not approved by the U.S. Food and Drug Administration for any human or veterinary use. As of September 29, 2023, the FDA placed TB-500 on the Section 503A Category 2 bulk drug substance list, prohibiting its preparation by compounding pharmacies for human use and citing concerns about immunogenicity and the absence of human exposure data. TB-500 and its parent molecule thymosin beta-4 are prohibited at all times under the World Anti-Doping Agency (WADA) Prohibited List.
The content of this guide is informational and reflects published peer-reviewed research, regulatory documents, and clinical trial registries as of June 2026. It is not medical advice, scientific advice for any specific application, or a recommendation for any use of any compound. The published literature on TB-500 side effects is incomplete, particularly with respect to the LKKTETQ fragment in human exposure contexts. Researchers should consult original peer-reviewed sources and follow all applicable institutional, local, and federal regulations governing the use, storage, and disposal of research chemicals.
Citations link to publicly accessible sources including PubMed, PubMed Central, ClinicalTrials.gov, the FDA, and the World Anti-Doping Agency. Phoenix Peptide Labs is not affiliated with the authors of the cited studies, with RegeneRx Biopharmaceuticals, or with any regulatory agency. Last reviewed: June 2026.