TB-500 Side Effects: What the Limited Research Shows

By DoseGauge Editorial · Updated 2026-06-14 · 7 min read

There is no FDA label for TB-500, and there is essentially no human safety data. That matters here, because a side-effect list normally comes from human trials or a prescribing document that an agency has reviewed, and for TB-500 neither exists. So a side-effect list cannot be drawn from those sources, because those sources are not there. What follows is what the limited research, which is largely preclinical, and the research context can support, with that limitation stated plainly. There is also one concrete, documented consequence: TB-500 is banned in sport at all times, so for a competitive athlete a positive test means sanction. This page is informational and educational only, not medical advice, and it does not recommend TB-500 or any dose. For background, see what tb-500 is.

Why there is no established side-effect list

For an FDA-approved drug, the side-effect section comes from a prescribing document. A regulator has reviewed clinical-trial data, the manufacturer has reported adverse events at known frequencies, and the result is a label you can cite. TB-500 has none of that. It is a research peptide, not approved by the FDA for any indication, so there is no prescribing information, no agency-reviewed adverse-event table, and no validated list of side effects with frequencies attached.

It goes further than a missing label. There are no human safety trials of TB-500 itself. The peer-reviewed reviews most often cited for it study thymosin beta-4, the parent protein, and summarize preclinical research: cell-culture and animal experiments (Xing et al., 2021; Maar et al., 2021). Neither review contains a human safety table or a record of adverse events in people taking TB-500. The human exposure that has been studied involved the full protein in early-stage trials, not the synthetic fragment sold as TB-500.

That is the honest starting point. Anyone presenting a confident, label-style list of TB-500 side effects, complete with percentages, is presenting something that does not exist in the literature. The accurate framing is qualitative: what the route of administration implies, and what the studied mechanism suggests researchers would watch, with the gaps named rather than filled in.

What the research context suggests

Two kinds of qualitative consideration are available, and neither is a documented human side-effect rate.

The first is injection-related. TB-500 sold for research is given by subcutaneous injection, and injection-site reactions (redness, itching, swelling, or soreness at the spot) are a common-sense expectation for any subcutaneous peptide. This is not specific to TB-500; it follows from the route of administration rather than from anything established about the compound.

The second comes from the studied mechanism, and it has to be stated carefully. The cited reviews describe thymosin beta-4 as pro-angiogenic: it promotes angiogenesis, the formation of new blood vessels, with reported upregulation of VEGF and signaling through pathways such as PI3K/Akt/eNOS (Xing et al., 2021; Maar et al., 2021). Because tumors depend on building their own blood supply, a peptide that promotes blood-vessel growth is the reason researchers raise malignancy as a theoretical concern for this class. That is reasoning from mechanism. It is not a report of what has happened in people. There is no human evidence that TB-500 causes cancer, no human study showing it does, and no human adverse-event rate of any kind to quote here. One of the cited reviews notes that thymosin beta-4's role in tumor biology is itself unresolved in the literature (Maar et al., 2021), which is another way of saying the question is open, not answered. The honest point is narrow: a pro-angiogenic mechanism is why the concern is raised at all, and the absence of human data is exactly why it cannot be confirmed or dismissed.

The sport-ban consequence

One consequence of TB-500 is concrete and documented, even though its clinical side effects are uncharacterized: the sport ban. The World Anti-Doping Agency prohibits TB-500 and thymosin beta-4 at all times under the Prohibited List, category S2.3 (Growth Factors and Related Substances). At all times means in and out of competition, not only on event day.

For a competitive athlete, this is not a theoretical risk. A test that returns positive for TB-500 or its metabolites means sanction regardless of intent, and the burden does not turn on whether the athlete felt any effect. So while the medical side-effect profile is unknown, the career and eligibility consequence for anyone subject to anti-doping rules is real, defined, and enforced.

The biggest risk is the missing data

The most important thing to say about TB-500 side effects is what is missing. There are no long-term human safety studies of TB-500, and there is no human trial large enough or long enough to characterize uncommon or delayed effects. The absence of that data is not reassurance. It is itself the central risk.

Uncharacterized risk is not the same as low risk. When a compound has never been studied for safety in people over time, the honest description is that its risks are unknown, not that they are small. Effects that take months or years to appear, or that show up only in a fraction of users, are exactly the kind that no preclinical study can detect. This is why the page does not, and cannot, tell you TB-500 is safe, and why it recommends nothing.

DoseGauge does not assess safety, and the calculator on this site does not either; it performs reconstitution and unit math on the values you enter and makes no judgment about whether a dose, or the compound itself, is appropriate for you. Whether any research peptide is appropriate for a specific person is a clinical question for a licensed clinician.

Frequently asked questions

What are the side effects of TB-500?

There is no FDA label and no human safety trials, so there is no agency-reviewed list of side effects with frequencies. The published research is largely preclinical, and the cited reviews study the parent protein, thymosin beta-4, with no human adverse-event data for TB-500 (Xing et al., 2021; Maar et al., 2021). Qualitatively, injection-site reactions are a common-sense consideration for any subcutaneous peptide, and because thymosin beta-4 is pro-angiogenic, malignancy is raised as a theoretical concern for this class. Those are reasoning from route and mechanism, not documented human adverse-event rates, and a meaningful human side-effect profile for TB-500 is not established.

Is TB-500 safe?

This page cannot call it safe. There is no human safety data for TB-500 and no FDA approval, so there is no basis to make that claim. Uncharacterized risk is not the same as low risk: a compound that has not been studied for safety in people has unknown risks, not small ones. TB-500 is also banned in sport at all times by WADA. A safety question about a specific person is a clinical question for a licensed clinician.

Does TB-500 cause cancer?

There is no human evidence that TB-500 causes cancer. No human study has shown that it does, and long-term human data simply do not exist. The reason the question gets asked is mechanistic: thymosin beta-4, the protein TB-500 is derived from, is pro-angiogenic (it promotes the growth of new blood vessels), and because tumors depend on a blood supply, researchers note malignancy as a theoretical concern for peptides in this class (Xing et al., 2021; Maar et al., 2021). One cited review describes thymosin beta-4's role in tumor biology as unresolved (Maar et al., 2021). That is a theoretical concern reasoned from mechanism, not a demonstrated human outcome, and the absence of human data is exactly why it cannot be confirmed or ruled out.

Will TB-500 make me fail a drug test?

Yes. The World Anti-Doping Agency prohibits TB-500 and thymosin beta-4 at all times under the Prohibited List, category S2.3 (Growth Factors and Related Substances). A competitive athlete who tests positive for TB-500 or its metabolites is subject to sanction regardless of intent, in or out of competition.

Informational and educational only. Not medical advice. DoseGauge computes from the values you enter and does not recommend a dose. Talk to a licensed clinician before using any peptide or GLP-1 medication.