What are the side effects of thymosin beta-4?

TB-500 and thymosin beta-4: the same molecule?

TB-500 is a synthetic fragment of thymosin beta-4, the 43-amino-acid protein the body produces naturally. The fragment keeps the active cell-migration region in a shorter, easier-to-synthesize form. Research literature — and search queries — use the two names interchangeably, though strict pharmacology references distinguish the full endogenous protein from the synthetic fragment.

For how the fragment compares with BPC-157 as a research peptide, see the BPC-157 vs TB-500 comparison.

What human safety data actually exists

Human exposure to thymosin beta-4 is limited to two RegeneRx-sponsored Phase 2 trials — in pressure ulcers (NCT00382161) and epidermolysis bullosa (NCT00311766) — both terminated for non-efficacy reasons such as patient availability and drug expiration, not for safety findings. Neither produced a published adverse-event dataset. There are no completed Phase 3 trials and no long-term human safety data.

What the cited studies examined

The literature cited on the profile studies mechanism and wound healing — actin binding, cell migration, angiogenesis, and tissue repair — largely in animal models. These studies were not designed to characterize side effects, so they neither report nor rule out adverse effects in humans. Claims that TB-500 has “no side effects” reflect this absence of study rather than evidence of safety.

The tumor-growth question

Because thymosin beta-4 promotes cell migration and angiogenesis — the growth of new blood vessels — a theoretical question has been raised about whether it could stimulate existing tumors. The cited literature does not resolve this: those studies were designed to measure wound-healing and regenerative activity, not malignancy risk, and no cited trial assessed it in humans. The question is open, not answered, in the sources this profile cites.

• No human trial has characterized the side effects of thymosin beta-4 / TB-500.
• Human exposure is two Phase 2 trials, both terminated for non-efficacy, with no published safety data.
• The cited studies examine wound-healing mechanism in animal models, not adverse effects.
• The theoretical tumor-stimulation question is not resolved by the cited literature.