Short answer: the natural protein TB-500 is modelled on, thymosin beta-4, has actually been given to people in clinical trials, and it was well tolerated. That is more human data than BPC-157 has. But there is a catch most articles skip: what is sold as “TB-500” is often not the same molecule that was tested. And the one serious concern researchers keep raising, a possible link to tumour growth and spread, has never been ruled out. Here is what the trials show, what they do not, and why the label on the vial matters more than usual.
Search “TB-500” and Google’s next suggestion is “TB-500 side effects.” It is the same pattern we saw with BPC-157: people are interested, and they are cautious. With TB-500 the caution is a little better informed, because there is real clinical data to look at. You just have to read it carefully.
TB-500 vs thymosin beta-4: not the same thing
Thymosin beta-4 (Tβ4) is a 43-amino-acid protein found in almost every human cell. Its main job is to hold on to actin, the building block cells use to change shape and move. That is why it shows up in wound-healing and tissue-repair research.
“TB-500” is a trade name, not a scientific one. Depending on the supplier it can mean a synthetic copy of the full 43-amino-acid protein, or a short fragment of 7 amino acids (Ac-LKKTETQ, the 17–23 region thought to drive actin binding). These are different molecules with different behaviour in the body.
| Thymosin beta-4 (full length) | “TB-500” fragment | |
|---|---|---|
| Length | 43 amino acids | Usually 7 amino acids (Tβ4 17–23) |
| Tested in human trials? | Yes, phase 1 to phase 3 | No published human trials |
| What the safety data covers | The full protein, mostly pharmaceutical-grade | Essentially nothing in humans |
Why it matters: when someone says “TB-500 has been tested in humans,” they are usually citing thymosin beta-4 trials. Those results do not automatically apply to a fragment. Check the COA: the molecular weight tells you which one you have (about 4,960 Da for full-length Tβ4, around 890 Da for the acetylated 7-amino-acid fragment).
What the human trials show
Thymosin beta-4 has been through more human testing than most research peptides, largely through the US company RegeneRx and, more recently, groups in China.
- Intravenous phase 1, healthy volunteers (USA, 2010). Ruff and colleagues gave single and repeated IV doses of Tβ4 to healthy adults against placebo, at doses up to 1,260 mg. They reported no dose-limiting toxicity and no serious adverse events attributed to the drug.
- First-in-human phase 1 of recombinant Tβ4 (China, 2021). A randomized, double-blind, placebo-controlled single- and multiple-dose study in healthy volunteers, which also reported the protein was well tolerated.
- Eye drops (RGN-259), phase 2 and 3. Tβ4 eye drops were tested for dry eye (the ARISE trials) and for neurotrophic keratopathy (SEER-1). Safety was good across these trials. Efficacy results were mixed: several primary endpoints were missed.
- Skin and heart programs. A topical gel for skin wounds and an injectable program for heart attack patients reached early clinical stages, but did not produce an approved product.
Put together, this is a reasonable short-term safety record for the full protein. Three limits are worth naming: most trials were short (days to weeks), several used routes other than injection (eye drops, gel), and none tested the 7-amino-acid fragment that is often sold as TB-500.
Fatigue, headache, lethargy: the reported effects
Online, the effects people describe most often are temporary fatigue or “lethargy,” headache, and redness or irritation where it was injected. Some also mention light-headedness or flushing. These come from forum reports, not controlled studies.
| What people report | In the clinical trials? | How to read it |
|---|---|---|
| Fatigue, lethargy | Not reported as a consistent drug effect | Anecdotal. Often reported after use, but no placebo comparison. |
| Headache | No clear drug-related signal reported | Common in any trial, drug or not. |
| Injection-site redness | Not applicable to eye-drop trials | Often linked to technique, pH or contamination rather than the peptide. |
| Flushing, dizziness | No clear signal | Plausible with any injected product, unproven for Tβ4. |
The cancer question
This is the serious one, and it is why anti-doping agencies are blunt about TB-500. Sport Integrity Australia, for example, warns of a “serious concern that it increases the spread and growth of cancer cells.”
The concern rests on biology, not on cases. Tβ4 helps cells move and helps new blood vessels form. Those are useful for healing, and they are also two things tumours rely on. Laboratory and tissue studies have found higher Tβ4 levels in some cancers, and in colorectal cancer, higher Tβ4 expression has been associated with invasion and distant metastasis. That is correlation, not proof that taking Tβ4 causes cancer. But no study has been long enough or large enough to rule it out, and it is the reason a doctor would hesitate with anyone who has a history of cancer.
Plain version: there is no evidence that TB-500 causes cancer in a healthy person. There is a credible theoretical reason it could help an existing tumour grow or spread, and the studies that would settle it have not been done.
The risk that is about the vial
As with every research peptide, the most measurable risk is often not the molecule but the product. Health Canada’s April 2026 advisory lists the practical dangers of unauthorized peptides: wrong dose (too much, too little or none), unlisted ingredients, and contamination with solvents, heavy metals, particles or microbes. TB-500 adds one more: you may not be getting the molecule you think, full protein or fragment.
The minimum standard is a batch-specific COA showing HPLC purity and mass-spectrometry identity, with a molecular weight that matches what the label claims. Our COA guide shows what to check line by line.
Health Canada, FDA and WADA
| Health Canada | Not authorized. Thymosin-β4 / TB-500 was among the products seized from Canada Peptide in 2025, and TB-500 is named in the April 2026 advisory on unauthorized injectable peptides. See what “research use only” does and does not mean legally. |
|---|---|
| FDA (USA) | Not approved. In July 2026 an FDA advisory committee narrowly recommended allowing pharmacy compounding of TB-500 with a prescription. The vote is non-binding and is not a drug approval. |
| WADA (sport) | Prohibited at all times under S2 (growth factors). No therapeutic use exemption is granted for it. |
Bottom line: the full thymosin beta-4 protein has a decent short-term human safety record. The fragment often sold as TB-500 has none. The open question is cancer, and it is a real one. If you are dealing with an injury yourself, a doctor or physiotherapist can offer options with stronger evidence.
See TrueLabs TB-500 and its COA →
Frequently asked questions
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What are the side effects of TB-500?
Clinical trials of the full thymosin beta-4 protein reported it was well tolerated, with no serious drug-related adverse events. Effects reported online, such as fatigue, headache and injection-site redness, are anecdotal. No human trial has tested the short TB-500 fragment.
Is TB-500 safe?
Short-term safety of full-length thymosin beta-4 looks reasonable in trials. Long-term safety has not been studied, and the fragment often sold as TB-500 has no human safety data.
Does TB-500 cause cancer?
No study shows it causes cancer. Because thymosin beta-4 promotes cell movement and blood-vessel growth, and higher levels have been linked to metastasis in some cancers, researchers consider it a theoretical risk, especially for anyone with existing cancer.
Is TB-500 the same as thymosin beta-4?
Not always. TB-500 can be a synthetic copy of the full 43-amino-acid protein or a 7-amino-acid fragment. The molecular weight on the COA tells you which one you have.
Is TB-500 legal in Canada?
TB-500 is not authorized by Health Canada and is named in its April 2026 advisory on unauthorized injectable peptides.
Is TB-500 banned in sport?
Yes. WADA prohibits thymosin beta-4 and its fragments at all times under category S2.
Related reading
- Ipamorelin side effects
- BPC-157 vs TB-500: roads vs trucks
- Buy TB-500 in Canada: price, research and buying guide
- BPC-157 side effects: what the research shows
References
- Ruff D, Crockford D, Girardi G, Zhang Y. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin β4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223–229. PubMed
- A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. 2021. PMC
- ClinicalTrials.gov. NCT02600429 (SEER-1, RGN-259 in neurotrophic keratopathy) and NCT00743769 (IV thymosin beta 4 phase 1). ClinicalTrials.gov
- Wang WS, et al. Overexpression of the thymosin beta-4 gene is associated with increased invasion of SW480 colon carcinoma cells and the distant metastasis of human colorectal carcinoma. 2004. PubMed
- Sport Integrity Australia. Thymosin beta-4 substance information. Sport Integrity Australia
- Health Canada. Think twice before injecting peptides bought online. Public advisory, April 9, 2026. Health Canada
- NPR. FDA panel considers easing peptide restrictions. July 23, 2026. NPR
All TrueLabs products are sold for in vitro and laboratory research use only. They are not intended for human or veterinary use, and nothing in this article is medical advice. If you have an injury or a history of cancer, please talk to a doctor.