TB-500 side effects

What is known in people

FDA found no clinical studies or human exposure data for TB-500 by any route.¹ It concluded that the potential safety risks in humans are unknown.¹ Its literature search found no article in which TB-500 was given to people.¹ A later human report, a 2026 series of 3 patients, used TB-500 mixed with other drugs.² So no study has measured how often any TB-500 side effect occurs.¹ The reports that do exist are grouped below by where they come from, followed by the risks regulators flag.

Reports involving TB-500

• FDA adverse event database (FAERS): a search through March 26, 2025 found no reports for TB-500, and FDA's literature search found no published adverse event cases.¹
• FDA complaint reports: FDA's system for food, supplement and cosmetic complaints held two reports from 2004 to March 10, 2025 about "blended TB-500 and BPC-157".¹ Neither included a safety assessment.¹
• 2026 case series (3 patients, TB-500 mixed with other drugs): the authors' summary table lists no adverse events for any of the 3 patients.² The series was small and uncontrolled, and the authors say questions about the safety of these peptides remain unresolved.²

Reports from thymosin beta-4 trials (a different molecule)

These trials tested the full 43-amino-acid parent protein. FDA says it is not the same substance as TB-500.¹ TB-500 has 7 amino acids.¹ The trials below used IV infusions, eye drops and a topical form, not the injections used in TB-500 animal studies.³⁴⁵¹ Their safety results describe a different molecule given by different routes.¹

• IV infusion, 40 healthy volunteers: a single dose, then the same dose daily for 14 days, at 42 to 1260 mg.³ Adverse events were infrequent and mild or moderate, with no dose-limiting toxicities or serious adverse events.³
• Eye drops, 9 patients with severe dry eye (phase 2): the drops were reported safe and well tolerated.⁴
• Eye drops, 18 patients with neurotrophic keratopathy (phase 3): no significant adverse effects were observed.⁶
• Topical treatment, 73 patients with venous leg ulcers (phase 2): the safety profile was comparable to placebo.⁵

Serious risks regulators and reviewers flag

These are potential risks named by FDA and by review authors, not side effects measured in people using TB-500.

• Immune reactions (immunogenicity): FDA warns that injected peptides like TB-500 may trigger an immune response.¹ Outcomes range from antibodies with no apparent symptoms to life-threatening and catastrophic reactions.¹ Neutralizing antibodies could weaken a drug's effect or even block the body's own matching peptide.¹ FDA adds that aggregation and peptide-related impurities may amplify this risk for TB-500.¹ Its compounding safety page makes the same point for compounded TB-500 and notes that FDA has identified no human exposure data.⁷
• Route and immune risk: FDA says that, in general, under-the-skin dosing is linked to more immune reactions than intramuscular or IV dosing.¹ FDA found no clinical studies of TB-500 by any route.¹
• Aggregation and degradation: FDA says peptides like TB-500 can be extremely sensitive to formulation, processing, pH, heat, concentration, impurities and added ingredients.¹ Those conditions may lead to aggregation and degradation, and FDA names aggregation as a factor that may amplify immune risk.¹
• Contamination and impurities: a 2026 review of unregulated injectable peptides lists product contamination and manufacturing impurities among their severe potential risks.⁸ The same review says TB-500 lacks an established human safety profile.⁸
• Unknown cancer risk: FDA found no carcinogenicity studies of TB-500.¹ SW480 colon cancer cells made to overproduce thymosin beta-4 became markedly more invasive in the lab.⁹ In patients, thymosin beta-4 mRNA was relatively higher in colorectal cancer liver metastases than in the matched primary tumors.⁹ Whether TB-500 affects cancer risk is unknown.¹
• Uncertain product identity: FDA has encountered several salts and derivatives marketed as TB-500, some with a different active molecule.¹ A representative certificate of analysis that FDA found did not test assay, impurities, bacterial endotoxins or aggregates.¹
• Scarce data overall: a 2026 Sports Medicine review covered approved and unapproved peptide therapies for musculoskeletal injuries and athletic performance.¹⁰ It says rigorous human safety data for many unapproved peptides are scarce, with potential for serious harm to patients.¹⁰

Warnings

• No safety testing: FDA found no nonclinical toxicity studies of TB-500 or TB-500 acetate, including none on development or reproduction.¹
• No long-term data: the longest TB-500 exposure in these studies is 4 weeks, in rats and in the 3-patient case series.¹¹² The rat study's authors call for longer-term studies.¹¹
• Pregnancy and breastfeeding: with no reproductive studies and no human exposure data, there are no data on use in pregnancy or breastfeeding.¹
• Combining with other peptides: no safety data exist for blends.¹ FDA's only complaint reports involved blended TB-500 and BPC-157.¹ A dissenting member of FDA's advisory committee raised concern about TB-500 being used with other peptides.¹²
• Athletes: TB-500 is prohibited at all times under WADA class S2.3.¹³ USADA gave a triathlete a four-year ban for possessing and using BPC-157 and TB-500.¹⁴
• Research-use labels: in a 2023 warning letter, FDA said website evidence showed an online seller's "TB-500" was intended for human use despite "research purpose only" labeling.¹⁵ It called the products new drugs that are not generally recognized as safe and effective.¹⁵

Related pages

The overview is in What is TB-500?. Study doses are on TB-500 dosage, and reported results on TB-500 benefits and uses. Storage and lab handling are on How to reconstitute TB-500. General lab safety is covered in safety basics. The research vial is listed under TB-500 for sale.