TB-500 Side Effects and Safety: What the Research Shows
What Are the TB-500 Side Effects, and How Common Are They?
Nobody knows how common TB-500 side effects are, because no published study has given TB-500 to people. FDA's 2026 review found no human studies, no published case reports and no reports in its main adverse event database. Its stated concerns are immune reactions to the injected peptide and impurities in the product.
That answer is less exciting than a list of symptoms. It is also what the record says. So this page sets out the record, source by source. Where a study exists, it is linked. Where none exists, the page says so.
TB-500 is a lab-made piece of a natural peptide called thymosin beta-4 (Tb4). It copies amino acids 17 to 23 of Tb4, with an acetyl group (a small chemical cap) added at the front. Its chain is Ac-LKKTETQ. Tb4 itself is 43 amino acids long. FDA notes studies found it widely expressed in various cell types. FDA stresses that TB-500 and Tb4 are not the same substance. That matters here. Almost all the human safety data belongs to Tb4.
For what TB-500 is claimed to do, read the TB-500 Complete Guide. For a head to head with the other big repair peptide, read BPC-157 vs TB-500. For TB-500 and hair growth, see our TB-500 hair growth page.
This content is for educational purposes only. These compounds are intended for research use. Nothing here is medical advice.
Which TB-500 Side Effects and Risks Matter Most?
Here is the whole record in one table. Each row names its source and the kind of evidence behind it.
| Side Effect / Risk | What the Record Shows | Evidence Type |
|---|---|---|
| Immune reaction to the injection | FDA says injected TB-500 may pose a significant risk of immunogenicity (the immune system reacting to the peptide). No study has tested it. | FDA review, 2026 |
| Impurities and clumping | FDA found no public test data on TB-500's impurities, aggregates (clumps of peptide) or bacterial endotoxin | FDA review, 2026 |
| Wrong substance in the vial | FDA found several salts and related molecules sold under the name TB-500 | FDA review, 2026 |
| Cancer promotion (theoretical) | Extra Tb4, the parent protein, grew more tumour blood vessels in rodent (mouse) melanoma models. No study has tested TB-500 for this. | Preclinical data on the parent protein |
| Reported side effects in people | No TB-500 reports in FDA's main adverse event database up to March 2025. One report on a BPC-157 and TB-500 blend describes skin and gum darkening. | FDA adverse event reports |
| Long-term and organ effects | FDA found no animal toxicity studies of TB-500 of any kind | FDA review, 2026 |
| Hormone effects | FDA found no human study of what TB-500 does in the body | FDA review, 2026 |
FDA's review sums it up in one line. The safety risks of TB-500 in humans are unknown. The closest human data comes from Tb4, a different substance. In a Phase I trial (a first, small safety study), four groups of 10 healthy volunteers took placebo (a dummy) or Tb4 into a vein. Doses ran from 42 to 1,260 mg, once and then daily for 14 days. Adverse events (any health problem during a trial) were infrequent and mild or moderate. There were no dose-limiting toxicities (side effects bad enough to cap the dose) and no serious events (Ruff et al., 2010).
How Do TB-500 Side Effects Start in the Body?
Nobody has measured how TB-500 acts inside a person. What exists is lab and animal work, most of it on Tb4. It points to two actions worth knowing.
Actin Binding and Cell Movement
TB-500 carries LKKTET, the stretch of Tb4 that binds actin. Actin is the protein that gives a cell its shape and lets it move. Tb4 holds a store of loose G-actin units (single actin building blocks). Cells draw on that store to change shape and move. Researchers have proposed that the LKKTETQ fragment may do the same job. FDA reports that as a hypothesis, not a finding. It also notes that the added acetyl group can change how the peptide acts.
One lab test cuts against the usual story. In a 2024 cell study, TB-500 itself did not significantly speed the closing of scratch wounds in fibroblasts (connective-tissue cells). One of its breakdown products, Ac-LKKTE, did. The authors suggest past healing reports may come from that breakdown product, not TB-500 (Rahaman et al., 2024). The same study found no cell toxicity from TB-500 or its breakdown products.
New Blood Vessels
Tb4 can also promote angiogenesis (new blood vessel growth). In animal heart studies reviewed by Srivastava et al. (2012), Tb4 helped heart muscle survive low oxygen. It also grew new heart vessels, which helped repair after injury. In adult animals, injected Tb4 improved heart function after an induced heart attack (Bock-Marquette et al., Int Immunopharmacol, 2023). Smart et al. (Angiogenesis, 2007) reviewed how Tb4 steers vessel growth, in wound healing and in tumour growth. The same vessel growth that helps repair is the root of the cancer question below.
Despite the shared name, thymosin alpha-1 is a different peptide, 28 amino acids long. Its data does not carry over to TB-500 either.
What Are the Common TB-500 Side Effects, and How Long Do They Last?
No one can answer this from data yet. A side effect rate needs people who took the drug and were watched. For TB-500, FDA found no such study. It found no human study of how the body takes up and clears it. It found no published case report either. So any list of common TB-500 side effects, with times and durations, is not drawn from a study.
What FDA's Adverse Event Searches Found
FDA searched FAERS, its adverse event reporting system, for TB-500 up to 26 March 2025. It found no reports. A second FDA database, for foods and supplements, held two reports on blended TB-500 and BPC-157. Neither included a safety assessment.
FDA's separate BPC-157 review describes one more FAERS report. A woman injected a product labelled for research use that held BPC-157 and TB-500. After a week, her skin and gums darkened. The same reaction came back when she used the product again, and stopped once she quit all peptides. FDA judged the product the likely cause. Because it held two peptides, FDA could not say which one.
An empty database is not a clean bill of health. FDA notes that reporting is voluntary. It does not receive every adverse event report, least of all for compounded (pharmacy-made) products.
Nausea, Flushing and Tiredness
You may have read that TB-500 causes nausea, skin flushing or tiredness in the first week. No study, published case report or FDA adverse event report in FDA's 2026 review records any of these for TB-500. They may happen. The record does not show them, or how long they last.
What the Tb4 Trials Recorded
Tb4, the parent protein, has been tested in people. In the Phase I trial above, adverse events were infrequent and mild or moderate. A Phase II trial (a larger test in patients) enrolled 72 people with leg ulcers caused by poor vein flow (venous stasis ulcers). They put a Tb4 gel or a placebo gel on the ulcer once a day, for up to 84 days. Serious adverse events hit 3 of 55 on Tb4 and 1 of 17 on placebo. The posted results mark each one as not related to Tb4 (NCT00832091). These results describe Tb4 on the skin or in a vein. They do not tell you what an injected TB-500 product does.
Injection Brings Its Own Risks
TB-500 is sold online as a powder. The withdrawn nomination planned shots under the skin or into muscle. FDA says injected peptides carry a special risk of an immune reaction. Such reactions can range from no symptoms at all to life-threatening ones. FDA adds that a shot under the skin tends to provoke more of them than a shot into muscle or a vein. Clumped peptide and impurities can raise the risk further.
FDA also found that a public certificate of analysis (a lab report on a batch) of TB-500 did not test for endotoxin. Endotoxin is toxic matter from the outer wall of some germs. Our certificate of analysis guide explains what each test on such a report covers. For how a powder is mixed with water, see our guide to reconstituting peptides.
Two warning signs need a doctor, whatever the product. Redness that spreads, with warmth, swelling, pus or fever, can mean a skin infection called cellulitis. Hives, a swollen face or tongue, chest tightness or trouble breathing can mean anaphylaxis, a severe allergic reaction. MedlinePlus, a US government health site, says to call 911 for severe symptoms.
Is There a TB-500 Cancer Risk from Angiogenesis?
Cancer is a theoretical risk, not a proven one. No study shows TB-500 causes cancer. FDA found no cancer studies of TB-500 at all. The worry comes from work on Tb4, the parent protein. It runs through blood vessel growth.
The Mechanism Behind the Worry
A 2003 study used mouse melanoma (skin cancer) cells. The cells were built to make extra Tb4 (Cha, Jeong, and Kleinman, JNCI, 2003, PMID 14625258). In rodent (mouse) models, tumours from those cells held 4.4 times more blood vessels. In lab tests the cells moved 2.3 times more. The tumours also grew larger, and more tumours formed in the lungs. The extra vessel growth came with higher VEGF (vascular endothelial growth factor). VEGF is a signal that grows new vessels.
Then came a 2011 tissue microarray study, which tests many small tissue samples on one slide (PMID 20975530). It found more thymosin beta-4 in osteosarcoma (a bone cancer) and colorectal (bowel) cancer tissue than in normal tissue. The study suggests the protein is linked to the tumourigenesis (tumour formation) of certain cancer types.
What the Headlines Miss
Correlation is not causation. Raised Tβ4 shows up in some tumours. That does not prove a TB-500 shot starts cancer in healthy tissue. High Tβ4 in a tumour does not tell us which came first.
TB-500 is not thymosin beta-4. The Cha et al. work used cells built to make extra full-length Tb4. It did not use TB-500 shots. So reading it straight across to a TB-500 dose adds one more layer of doubt.
The cancer data is mixed. In multiple myeloma, a blood cancer, a 2010 study found the opposite pattern. Myeloma cells made less Tb4 than normal cells. The study followed 209 patients after high-dose therapy and a stem cell transplant. Those with lower Tb4 did worse, with a shorter event-free survival. That is the time before the disease came back, got worse, or the patient died. The authors suggest Tb4 may hold this tumour back (Caers et al., 2010). So the link depends on the cancer type.
No trial could have recorded a TB-500 cancer. No trial has given TB-500 to people. The Tb4 Phase I trial reported no serious adverse events, but its dosing lasted 14 days. Nobody has tracked TB-500 users for years to see.
The Practical Bottom Line
For a healthy person with no known tumour, the record holds a theory, not a finding. The rodent data does raise a specific concern for anyone with active cancer or an unexplained lump. For them, extra vessel growth is the one effect the research points to. Anyone in that position should raise it with a qualified clinician.
Three Groups the Gaps in the Record Matter Most For
TB-500 has no approved label. So there is no official list of who should avoid it. The record does flag three groups. The table sets out each one and its source.
| Group | What the Record Shows | Source |
|---|---|---|
| People with active cancer or an unexplained lump | Extra Tb4 grew bigger, more vascular tumours in rodent (mouse) melanoma models | Cha et al., 2003 |
| Pregnancy or breastfeeding | FDA found no animal studies of TB-500 on fertility, pregnancy or offspring | FDA review, 2026 |
| Competitive athletes under WADA jurisdiction | Banned at all times, in and out of competition, under S2.3 (growth factors) | WADA 2026 Prohibited List |
Beyond those groups, the gap applies to everyone. With no human data, FDA says the risks to anyone are unknown.
What Do Studied Doses Tell Us About TB-500 Side Effects Risks?
Very little. There is no FDA-approved dose for TB-500. No dose has been tested in people. No study links any dose to a lower or higher side effect risk. What exists are the doses used in research, mostly in animals, plus the Tb4 trials. They are listed here as research protocols, not as guidance.
The Research Protocols on Record
| Substance | Study | Dose and Route | Subjects |
|---|---|---|---|
| TB-500 | Ho et al., 2012, in FDA's review | 10 mg once, under the skin | Horses |
| TB-500 | Rahaman et al., 2024 | 50 mg per kg once, into the belly cavity | Rodent (rat), young adult males |
| TB-500 | Withdrawn nomination, in FDA's review | 3 mg/mL powder, proposed for injection under the skin or into muscle | None; never tested |
| Tb4, a different substance | Ruff et al., 2010 | 42, 140, 420 or 1,260 mg into a vein, once and then daily for 14 days | 40 healthy volunteers, some on placebo |
| Tb4 gel, a different substance | NCT00832091 | 0.01%, 0.03% or 0.1% gel on the ulcer, daily for up to 84 days | 72 adults with venous stasis ulcers, 55 on Tb4 |
In the horses, TB-500 levels in blood peaked 60 to 120 minutes after the shot. They were too low to measure after 6 to 10 hours. Both horses and rats broke TB-500 into smaller pieces. Those pieces showed up in horse blood and in the urine of both.
FDA found websites selling TB-500 as 2, 3, 5, 10 and 15 mg powders labelled for research use only. No record ties any of those amounts to a safe dose in people. WADA does not class TB-500 with the peptides that make the body release growth hormone, such as ipamorelin and CJC-1295. Our secretagogue comparison covers that class.
For the stack that pairs TB-500 with BPC-157, read the Wolverine Stack guide. To see where TB-500 sits next to the rest, read the 2026 injury recovery peptide comparison.
BPC-157 and TB-500 Side Effects: How Do the Two Compare?
These two are sold in blends, as FDA's adverse event records show. FDA reviewed both for its July 2026 advisory meeting. Here is the split, row by row. It comes from those two reviews and the WADA List.
| Safety Parameter | TB-500 | BPC-157 |
|---|---|---|
| Human clinical trial data | None found by FDA | Five small, short studies (enema, joint, bladder and vein), none by mouth or under the skin |
| Serious adverse events in those studies | No study to report any | None appear to have been reported, FDA says, though safety monitoring was unclear in most |
| Animal toxicity studies | None found | Single-dose and 28-day studies in rats and dogs |
| Cancer (carcinogenicity) studies | None found | None found |
| Blood vessel growth | Parent protein Tb4 grew tumour vessels in rodent (mouse) models | Researchers have proposed it may induce angiogenesis |
| Immune reaction concern | Yes, for injection, per FDA | Yes, for injection, per FDA |
| FDA adverse event reports | None for TB-500 up to March 2025 | Three up to December 2025, all injected, one a blend with TB-500 |
| WADA prohibited status | Yes: S2.3, non-Specified Substance, all times | Yes: S0, Specified Substance, all times |
| FDA's 2026 proposal for the 503A list | Do not add | Do not add |
BPC-157 has more human and animal data than TB-500. Even so, FDA judged neither set of data strong enough to list them. Both raise the same worries about shots. Our BPC-157 dosing guide covers that peptide's research protocols.
The Legal and Regulatory Status of TB-500
TB-500 is not an FDA-approved drug. No pharmacy may make it up under section 503A today. The record below shows why.
United States
Section 503A of the drug law covers pharmacies that compound (custom-make) a drug. It lets them use a raw bulk ingredient in only three cases. The first is a USP or NF monograph (an official quality standard). The second is being part of an FDA-approved drug. The third is a place on FDA's 503A bulks list, 21 CFR 216.23. FDA's review found TB-500 has no monograph. It is not part of any approved drug. And the bulks list does not name it.
Here is its path through FDA's lists. A pharmacy group, Wells Pharmacy Network, put it forward for the 503A bulks list. In September 2023, FDA placed Thymosin Beta-4, Fragment (LKKTETQ) in Category 2. That is the group FDA says raises significant safety risks. On 22 April 2026, FDA took it out of Category 2, because the nomination was withdrawn. It did not move to Category 1. FDA still chose to review it for its advisory meeting on 23 July 2026. In that review, FDA proposed not adding TB-500 to the bulks list.
FDA's safety-risk page still lists TB-500, as a former Category 2 entry. It says TB-500 may pose a risk of immune reactions. It adds that FDA lacks key safety facts about it. FDA's meeting page notes that its advisers' votes do not bind FDA. Read what FDA's 2026 category changes mean for peptide access and the current legal status overview for the wider picture.
A "research use only" label does not change the picture. In December 2024, FDA sent a warning letter to Summit Research Peptides. It said such labels did not stop the products being unapproved new drugs. The seller's own website claims showed they were meant for people.
WADA and Competitive Sport
The 2026 WADA Prohibited List has been in force since 1 January 2026. It names "Thymosin-ß4 and its derivatives e.g. TB-500" under S2.3. That is the class for growth factors. It is banned at all times, in sport and out of it. Every S2 substance is a non-Specified Substance. WADA keeps the Specified label for substances more likely to be taken for reasons other than sport.
In April 2025, Canada's anti-doping agency (CCES) gave a university volleyball player a four-year ban. The athlete had used BPC-157 and TB-500. The case rested on information given to the CCES, not a positive test. If you compete, treat TB-500 as off-limits. See our WADA banned peptides overview for the full picture.
Other Jurisdictions
FDA's review found no approved TB-500 product in Canada, Australia, the UK, Belgium, Ireland, France, Norway, Germany, Spain or Italy. The EU's drug agency has cleared none either. For how grey-market supply fills that gap, see the grey-market peptide access problem.
FDA's Findings on TB-500 Product Quality
With no approved product, what is in a vial depends on who made it. FDA's review gives four reasons to be wary.
- The name is loose: TB-500 is a common name, not an official drug name. FDA has found several salts (chemical forms) and related molecules sold under it, some with a different active part. So a vial marked TB-500 may hold a different substance.
- Testing is thin: the public lab report FDA looked at covered only appearance, identity and purity. It did not test how much peptide was present. Nor did it test impurities, endotoxin or clumps.
- The paperwork did not match: the withdrawn nomination named TB-500 free base, the bare peptide. Its lab report was for TB-500 acetate, the peptide as a salt. FDA treats those as two different ingredients.
- Peptides are fragile: FDA notes that heat, pH (acidity) and impurities can make peptides clump or break down. That can cost them their activity.
Our recommended sources page sets out the seven tests we hold research suppliers to, endotoxin testing among them. For a full way to judge any supplier, read how to vet a peptide supplier.
Five Misreadings of the TB-500 Record
- Treating Tb4 data as TB-500 data. FDA says the two are not the same substance, and notes that many websites use the names interchangeably. Almost all the human data on this page is for Tb4.
- Reading no reports as safe. FAERS relies on voluntary reports. FDA does not receive every adverse event, especially for compounded products.
- Trusting a research-use label. FDA's letter to Summit Research Peptides treated products sold for people as drugs, whatever the label said.
- Assuming a blend is better understood. FDA found no study that gave TB-500 to people, alone or with BPC-157. The one detailed FDA report on a blend could not be pinned on either peptide. The peptide stacks that work guide covers how pairs are put together.
- Using an old WADA category. TB-500 sits in S2.3 on the 2026 List, not S0. BPC-157 is the one in S0.
Each of these treats a gap in the record as if it were an answer. The record is thin, and it helps to know exactly how thin.
How Good Is the TB-500 Side Effects Human Data?
An honest safety page has to grade its own proof. For TB-500 itself, FDA found no human data of any kind in its 2026 review. Everything else is borrowed from Tb4, from animals or from the lab. Any claim built on Tb4 research carries extra doubt. TB-500 is a fragment, not the whole molecule.
| Claim | Evidence Level | Source Type | Confidence |
|---|---|---|---|
| TB-500 side effects are mild and short-lived | No human data | FDA review, 2026 | Unsupported |
| No serious drug-related adverse events in published trials | Tb4 by vein: no serious adverse events in a 14-day Phase I trial. Tb4 gel: serious adverse events in 3 of 55 on Tb4 and 1 of 17 on placebo in a Phase II trial. The posted results mark every one as not related to Tb4 | Ruff et al. 2010; NCT00832091 | Supported for the parent compound (Tb4) in these two trials. No human data exists for TB-500 |
| Theoretical cancer promotion risk via angiogenesis | Preclinical mechanistic; cell line and animal models, plus human tumour tissue | Cha et al. JNCI 2003; tumour microarray data; Caers et al. 2010 | Mechanism confirmed in rodent (mouse) models; clinical translation unknown |
| Immune reactions to injected TB-500 | Regulator concern; no study | FDA review, 2026 | Unknown |
| Long-term safety | No toxicity studies of TB-500 of any length | FDA review, 2026 | Unknown; cannot be claimed safe long-term |
| TB-500 wound healing activity may derive from metabolite Ac-LKKTE | 2024 in vitro study (Rahaman et al., 2024) | Single study; requires replication | Low; hypothesis-generating only |
No serious adverse event appears in the published Tb4 trial by vein. The Tb4 gel trial recorded some, in both groups. The posted results mark those as not related to Tb4. That reassurance comes from Tb4 trials, not TB-500. It says nothing direct about an injected TB-500 product of unknown quality. So the record is incomplete, not clean.
Where to buy TB-500
The hard part with TB-500 isn't the protocol. It's finding a supplier that can prove what's in the vial. We assessed dozens against per-batch, third-party testing. A handful passed.
See the sources that passed →Bibliography and Primary Sources
- Cha HJ, Jeong MJ, Kleinman HK. Role of thymosin beta4 in tumor metastasis and angiogenesis. J Natl Cancer Inst. 2003;95(22):1674-1680. PMID 14625258
- Smart N, Rossdeutsch A, Riley PR. Thymosin beta4 and angiogenesis: modes of action and therapeutic potential. Angiogenesis. 2007;10(4):229-241. PMID 17632766
- Srivastava D, Ieda M, Fu J, Qian L. Cardiac repair with thymosin beta4 and cardiac reprogramming factors. Ann N Y Acad Sci. 2012;1270:66-72. PMID 23050819
- Jo JO, Kang YJ, Ock MS, Kleinman HK, Chang HK, Cha HJ. Thymosin beta4 expression in human tissues and in tumors using tissue microarrays. Appl Immunohistochem Mol Morphol. 2011;19(2):160-167. PMID 20975530
- Bock-Marquette I et al. Thymosin beta-4 denotes new directions towards developing prosperous anti-aging regenerative therapies. Int Immunopharmacol. 2023. PMID 36709593
- Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1235:124033. PMID 38382158
- Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223-229. PMID 20536472
- Caers J, Hose D, Kuipers I, et al. Thymosin beta4 has tumor suppressive effects and its decreased expression results in poor prognosis and decreased survival in multiple myeloma. Haematologica. 2010;95(1):163-167. PMID 19833631
- FDA. Evaluation of TB-500-related bulk drug substances for inclusion on the 503A bulk drug substances list. Briefing document, Pharmacy Compounding Advisory Committee, 23 to 24 July 2026. fda.gov/media/193349
- FDA. Evaluation of BPC-157-related bulk drug substances. Briefing document, Pharmacy Compounding Advisory Committee, 23 to 24 July 2026. fda.gov/media/193343
- RegeneRx Biopharmaceuticals. Study of Thymosin Beta 4 in Patients With Venous Stasis Ulcers. ClinicalTrials.gov NCT00832091
- FDA. Bulk drug substances nominated for use in compounding under section 503A, updated 14 May 2026. fda.gov/media/94155
This content is for educational purposes only. These compounds are intended for research use. Nothing here is medical advice. TB-500 is not an FDA-approved drug. Speak to a qualified clinician about any symptom after an injection.
Where to buy TB-500
The hard part with TB-500 isn't the protocol. It's finding a supplier that can prove what's in the vial. We assessed dozens against per-batch, third-party testing. A handful passed.
See the sources that passed →Share this article
Frequently Asked Questions
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Disclaimer: This content is for educational purposes only. These compounds are intended for research use. Nothing here is medical advice. Always work with a qualified clinician before making changes to your health protocol.