Safety
TB-500 side effects and safety: what is known and what is not
TB-500 side effects: what thymosin beta-4 trials reported, why FDA had no human data on the fragment, the theoretical risks in the literature and the WADA ban.
By Julian Caraulani · Updated October 30, 2026 · Reviewed by Dr. A. Goher, MBBS
Nobody knows TB-500's side effect profile in people, because no published controlled trial has tested it. FDA said it "has not identified any human exposure data" for the fragment (FDA). Trials of the parent protein, thymosin beta-4, reported mostly mild events. Prescription TB-500 starts at $149 a month; see TB-500 prices.
Compounded drugs are not FDA-approved, and the HHS policy that covers TB-500 is interim and can be withdrawn. Status checked on 30 October 2026.
What the thymosin beta-4 trials reported
TB-500 is a seven-amino-acid fragment of thymosin beta-4 (our TB-500 guide explains the difference). The safety data below come from the full protein, given as eye drops, skin gel or intravenous infusion. None of it tested injected TB-500, so it is indirect evidence at best.
| Study | Who and how | Adverse events reported |
|---|---|---|
| Ruff 2010 | 40 healthy volunteers, intravenous, up to 14 days | Infrequent, mild or moderate; no serious events |
| Wang 2021 | Healthy volunteers, recombinant protein, intravenous | Mild to moderate; no serious events |
| Guarnera 2010 | 73 people with venous leg ulcers, topical gel | Safety comparable to placebo |
| NCT00832091 | Same venous ulcer program, registry results | Serious events in 3 of 55 on the protein, 1 of 17 on placebo |
| ARISE-3, NCT03937882 | About 700 people with dry eye, eye drops | No serious events in either group; instillation site pain in 23 of 350 on the drops, 16 of 349 on placebo |
| SEER-1, NCT02600429 | 18 people with neurotrophic keratopathy, eye drops | One serious event (depression) in 10 on the drops, none in 8 on placebo |
The Ruff team reported: "Adverse events were infrequent, and mild or moderate in intensity. There were no dose limiting toxicities or serious adverse events" (Ruff 2010, PubMed 20536472). The Chinese Phase 1 of a recombinant version found "The adverse events were mild to moderate in intensity" (Wang 2021, PubMed 34346165). Its authors included employees of the sponsor, as the paper discloses.
Three points limit what these numbers say about TB-500. The products were different molecules. The routes were different: most were on the skin or the eye, not injected under the skin. And each trial lasted weeks, not months or years.
What is unknown
FDA reviewed the fragment when it was nominated for compounding and wrote that it "lacks important information regarding any safety issues raised by this drug, including whether it would cause harm if administered to humans" (FDA). Specific gaps:
- Immune reactions. FDA flagged that TB-500 "may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation as well as peptide-related impurities" (FDA). Immunogenicity means the body may form antibodies against the product.
- Long-term effects. No study followed people on the fragment over time.
- Pregnancy, breastfeeding, children and older adults. We found no human data for TB-500 in any of these groups.
- Interactions with other medicines have not been studied.
HHS took a different view when it added TB-500 to its interim policy. It wrote that the safety concerns raised by FDA's drug center "are inferential rather than observed, the parent protein has a controlled human safety record across several routes, and the fragment is rapidly truncated in human serum" (HHS policy, Appendix B). Both statements can be true at once: no harm has been observed, partly because almost nothing has been measured.
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Theoretical concerns in the literature
Thymosin beta-4 helps cells move and helps grow new blood vessels. Those are the properties marketed for healing, and the same properties raise a question about tumours. A 2012 review stated that "Tβ4 played a key role in facilitating tumor metastasis and angiogenesis" and that it "expressed increasingly in a number of metastatic tumors" (Xiao 2012, PubMed 22856429). That is laboratory and tissue research on the full protein, not a finding that TB-500 causes cancer in people.
A 2026 clinical review of unregulated injectables, which names TB-500, lists potential risks including "product contamination, manufacturing impurities" ... "pathological angiogenesis, carcinogenesis, cardiovascular stress" (Moiz 2026, PubMed 42757290). These are risks the authors consider plausible, not observed rates. Anyone with a current or past cancer should raise it with an oncologist before considering TB-500.
Quality risks
For a peptide with thin safety data, what is in the vial matters as much as the molecule. A 2026 orthopaedic review warned that "Commercial products marketed also raise concerns regarding identity, purity, concentration, sterility, and manufacturing consistency" (Tham 2026, PubMed 42937313).
The HHS policy was written partly to address this. It says the Secretary aims to "discourage the continued, widespread use of certain research-use-only peptides supplied by foreign manufacturers that pose a safety risk to US patients" (HHS policy). For compounding under the policy, the ingredient must come from an FDA-registered manufacturer with a lot-specific certificate of analysis that covers identity, purity and contaminants such as endotoxins, and compounders must report serious adverse events to FDA's MedWatch program. The label must read "This is a compounded drug product. Not for resale." (HHS policy).
Research-use-only products sold without a prescription carry none of those conditions. Our research vs prescription peptides and compounded peptide safety guides cover what to ask a pharmacy.
Sports and anti-doping
TB-500 is banned for tested athletes regardless of prescription. WADA's 2026 list names "Thymosin-ß4 and its derivatives e.g. TB-500" among growth factors that are "PROHIBITED AT ALL TIMES (IN- AND OUT-OF-COMPETITION)" (WADA 2026 Prohibited List). Anti-doping labs have built tests for it: the Ghent laboratory that identified the fragment also proposed "an analytical strategy for detection in plasma and urine" (Esposito 2012, PubMed 22962027). A positive test can mean a suspension, so athletes should ask their anti-doping organisation before any use.
What to ask your prescriber
Superpower, the one program in our table offering TB-500 on 30 October 2026, says plainly that "These treatments carry known and unknown risks" (Superpower). Before you start, ask:
- Which pharmacy compounds the product, and can you see the certificate of analysis for the ingredient lot.
- Which blood tests come before and during treatment, and whether they are in the price. Compare on the Superpower review.
- How to report a reaction, and what should make you stop and call: spreading redness, swelling or pain at the injection site, rash, breathing trouble or any allergic-type reaction.
- Whether your history (cancer, pregnancy plans, other medicines) changes the advice.
Your prescriber sets how TB-500 is used; we do not publish doses or protocols.
FAQ
What are the side effects of TB-500?
TB-500 side effects in people are unknown, because no published controlled trial has tested the fragment. Trials of the full protein, thymosin beta-4, reported mostly mild or moderate events, including eye discomfort with eye drops. Those trials used different products and routes, so they cannot predict what injected TB-500 does. Report any reaction to your prescriber.
Is TB-500 safe?
Safety has not been established. FDA said it found no human exposure data for the fragment and flagged a possible immune reaction risk. HHS judged those concerns inferential rather than observed and allowed 503A compounding under conditions. Neither view comes from a trial of TB-500, and compounded products are not FDA-reviewed for safety.
Does TB-500 cause cancer?
No study shows that TB-500 causes cancer in people, and none was designed to test it. Laboratory reviews link the full thymosin beta-4 protein to tumour cell movement and blood vessel growth, which is why some authors list carcinogenesis as a theoretical risk. People with a cancer history should ask their oncologist first.
Can TB-500 cause injection site reactions?
Nobody has measured it, because there is no TB-500 trial. Programs and prescribers watch for redness, swelling and pain at the site as with other injected compounded drugs. In the ARISE-3 eye drop trial of thymosin beta-4, instillation site pain was reported by 23 of 350 people on the drops and 16 of 349 on placebo. Ask your prescriber which site reactions warrant a call.
Will TB-500 show up on a drug test?
Anti-doping tests can detect it. WADA's 2026 list prohibits thymosin beta-4 and its derivatives, naming TB-500, at all times. Laboratories have published methods for detecting the fragment in plasma and urine. A prescription does not protect a tested athlete, who would need a Therapeutic Use Exemption.
Is prescription TB-500 safer than research-use-only TB-500?
The molecule is the same, but the controls differ. Under the HHS policy, the ingredient must come from an FDA-registered maker with lot testing for identity, purity and contaminants, a clinician must prescribe, and serious adverse events must be reported. Research-use-only products have none of those requirements, and their contents are often unverified.
Compare prescription TB-500 programs on price, labs and oversight on the best peptide programs page.