TB-500: Side Effects & Safety
Part of the TB-500 Complete Guide
TB-500
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Overall Safety Profile
TB-500 is a synthetic fragment of naturally occurring thymosin beta-4, which is present in nearly all mammalian cells at high concentrations. Research studies have generally reported a favorable safety profile, with most side effects being mild and transient.
However, large-scale human clinical trials have not been completed for TB-500 specifically. Its parent molecule thymosin beta-4 has more clinical data — RegeneRx Biopharmaceuticals conducted Phase 2 trials for wound healing and corneal repair with acceptable safety profiles.
For general peptide safety information, see Are Peptides Safe?
Reported Side Effects
| Side Effect | Frequency | Severity | Notes |
|---|---|---|---|
| Injection site reactions | Common | Mild | Redness, irritation, bruising — standard SC injection effects |
| Headache | Occasional | Mild | More common during loading phase, typically resolves |
| Lethargy / fatigue | Occasional | Mild | First few days of use; body typically adjusts |
| Nausea | Occasional | Mild | More common at higher doses |
| Head rush / lightheadedness | Occasional | Mild | Transient, shortly after injection |
Most side effects are mild, dose-dependent, and resolve with continued use. Headache and fatigue during the loading phase are the most commonly cited reasons for concern, but they are typically transient.
Safety Limitations & Concerns
Angiogenesis & cancer: TB-500 promotes cell migration and angiogenesis (new blood vessel formation). Like BPC-157, these properties raise theoretical concerns about use in individuals with undiagnosed cancers, where enhanced blood supply and cell migration could theoretically support tumor growth. No published research has demonstrated cancer-promoting effects, but the concern is mechanistically plausible.
Other limitations:
- Long-term safety studies in humans are absent
- Thymosin beta-4 is on the WADA prohibited substances list (S2 category) — competitive athletes cannot use TB-500
- Not studied in pregnant or breastfeeding individuals
- Drug interaction data does not exist
Contraindications
- Active cancer or cancer history: Angiogenic and cell-migration-promoting effects
- Pregnancy and breastfeeding: No reproductive safety data
- Known hypersensitivity to thymosin peptides
- Competitive athletes: Banned by WADA — will cause a positive doping test
Return to the TB-500 overview for general information. Compare safety with BPC-157 side effects.