Thymosin Beta-4 is a thymic peptide and research chemical that is 43 amino acids long. Thymosin Beta-4 is not a thymic hormone in the true sense of the word, but is found in many tissues throughout the human body. The thymosins were isolated by Allan Goldstein in the 1960s, with recognition of clinical and therapeutic potential coming in later decades.[1] Thymosin Beta-4 has recently been marketed extensively for performance enhancement in horses, where regulation is nonexistent relative to the human pharmaceutical industry. When TB4 is sold as a performance enhancement drug for greyhounds, horses, and other racing animals it is marketed under the name TB-500.