Published · 8 references
TB-500 vs Thymosin Alpha-1
TB-500 and Thymosin Alpha-1 are different molecules: TB-500 is a seven-residue fragment of Thymosin Beta-4, and Thymosin Alpha-1 is a 28-residue peptide whose sequence matches part of prothymosin alpha.
Structure at a glance
TB-500 · 7 residues
Thymosin Alpha-1 · 28 residues
Ac: N-terminal acetyl group. Letters are one-letter amino acid codes.
Drawn from the product database. Each measure's bars share one scale.
| Property | TB-500 | Thymosin Alpha-1 |
|---|---|---|
| What it is | A synthetic seven-residue peptide corresponding to residues 17 to 23 of Thymosin Beta-4. | A synthetic 28-residue peptide whose sequence matches residues 2 to 29 of prothymosin alpha; its international nonproprietary name is thymalfasin. |
| How they relate | Different molecules from different parents. TB-500 corresponds to residues 17 to 23 of Thymosin Beta-4. The sequence of Thymosin Alpha-1 matches residues 2 to 29 of prothymosin alpha. | |
| CAS number | 885340-08-9 | 62304-98-7 |
| Molecular formula | C38H68N10O14 | C129H215N33O55 |
| Molecular weight | 889.02 g/mol | 3,108.31 g/mol |
| Sequence | Ac-LKKTETQ | Ac-SDAAVDTSSEITTKDLKEKKEVVEEAEN |
| Target | No target established for TB-500, which contains the actin-binding motif of Thymosin Beta-4.[1] | No target established for Thymosin Alpha-1. |
| Evidence base | Cell-culture and explant assays tested a peptide with its seven-residue sequence.[1] An aged-mouse study tested a synthetic peptide with that sequence.[2] Attributed activity not directly determined with TB-500 itself in animal or human studies, in the literature reviewed for it. | Randomized human trials. The largest, of 1,106 participants, in one indication, found no significant difference overall on the measures reported for it.[3] Two registered trials are listed as completed but unpublished.[4] |
| Regulatory status | The FDA has not approved TB-500 for human use. | A medicine containing thymalfasin holds a national marketing authorization in Italy, in one indication.[5] The FDA has approved no drug product containing it.[6] FDA granted four orphan designations, each in one indication; each record reads not approved for that indication.[7] |
| Compared head-to-head? | No direct comparison found in PubMed (searched October 2026).[8] | |
| Handling difference | Neither contains a cysteine or a methionine. TB-500's charge is close to balanced; Thymosin Alpha-1 has a strongly acidic composition, with very few basic side chains. | |
| Where they get confused | In the research-chemical market, the name TB-500 is sometimes applied to full-length Thymosin Beta-4. Thymosin Alpha-1 and Thymosin Beta-4 share part of a name and little else. | |
How TB-500 and Thymosin Alpha-1 differ
TB-500 and Thymosin Alpha-1 are different molecules from different parents. TB-500 is a synthetic seven-residue peptide. Thymosin Alpha-1 is a synthetic 28-residue peptide whose sequence matches residues 2 to 29 of prothymosin alpha. Its international nonproprietary name is thymalfasin. Thymosin Alpha-1 is a separate molecule from TB-500, with its own evidence base.
TB-500 corresponds to residues 17 to 23 of Thymosin Beta-4, and in the literature reviewed for TB-500, most studies used the full-length parent rather than a peptide with TB-500's sequence. Evidence for Thymosin Beta-4 does not transfer to Thymosin Alpha-1.
A peptide with TB-500's seven-residue sequence was tested in cell-culture and explant assays.[1] A synthetic peptide with the same sequence was also tested in aged mice.[2] TB-500 supplies that sequence in N-acetylated form. In the literature reviewed for TB-500, the activity attributed to it has not been directly determined with TB-500 itself in animal or human studies. Much of the foundational work in that literature comes from a relatively small number of groups, and the proposed mechanisms are not fully resolved. The literature reviewed for TB-500 reports no human safety data.
The human record reviewed for Thymosin Alpha-1 includes randomized trials. The largest, of 1,106 participants, in one indication, found no significant difference overall on the measures reported for it.[3] In that trial, no safety outcome differed from placebo overall, and one prespecified subgroup showed higher mortality on the drug than on placebo, a hypothesis-generating finding.[3] FDA's review also cites reports of fatal immune hemolytic anemia and engraftment failure in transplant recipients; such reports cannot show cause or frequency.[6] Two registered trials, each for 500 patients, are listed as completed but unpublished.[4] In the literature reviewed for Thymosin Alpha-1, its developer funded or sponsored the pivotal trials, including those that returned null results.
The FDA has not approved TB-500 for human use. It has approved no drug product containing thymalfasin.[6] Thymalfasin is the active ingredient of a medicine authorized in Italy, in one indication.[5] The material supplied here is a research-grade preparation, is not that medicine, and holds no marketing authorization. The Italian authorization belongs to thymalfasin alone. The FDA granted four orphan designations for thymalfasin, and each record reads not approved for its indication.[7] A designation is a development incentive rather than a marketing approval.
Have TB-500 and Thymosin Alpha-1 been compared directly?
No direct comparison was found in a PubMed search run in October 2026.[8] That search covers PubMed only.
Read more on each compound
TB-500
Frequently Asked Questions
Is TB-500 the same as Thymosin Alpha-1?+−
No. TB-500 and Thymosin Alpha-1 are different molecules from different parents. TB-500 is a seven-residue fragment of Thymosin Beta-4, and Thymosin Alpha-1 is a 28-residue peptide whose sequence matches part of prothymosin alpha. Thymosin Alpha-1 and Thymosin Beta-4 share part of a name and little else.
Is TB-500 or Thymosin Alpha-1 approved?+−
Neither TB-500 nor Thymosin Alpha-1 has an FDA approval; the FDA has approved no drug product containing thymalfasin, the international nonproprietary name for Thymosin Alpha-1. Thymalfasin is the active ingredient of a medicine authorized in Italy. The material supplied here is a research-grade preparation, is not that medicine, and holds no marketing authorization.
References
- 4ClinicalTrials.gov registry records NCT00040027 and NCT00039962. Both completed, enrollment 500 each, hasResults false. Retrieved via API v2 on 28 August 2026, with a PubMed search for either identifier returning zero records.
- 5European Medicines Agency. Public register entry, orphan designation for thymalfasin, designated 30 July 2002. Retrieved 28 August 2026.
- 6US Food and Drug Administration, Center for Drug Evaluation and Research. Briefing presentation, 4 December 2024. fda.gov
- 7US Food and Drug Administration, Office of Orphan Products Development. Orphan drug designation database, four thymalfasin designations, 1991 to 2006. Each record's FDA Orphan Approval Status field reads "Not FDA Approved for Orphan Indication". Reported as previously recorded rather than read live, 28 August 2026.
- 8PubMed search via NCBI E-utilities, run 3 October 2026; records entered to 2 October 2026. Query: ("TB-500"[tiab] OR "TB500"[tiab] OR "TB 500"[tiab] OR "LKKTETQ"[tiab] OR "Ac-LKKTETQ"[tiab]) AND ("thymosin alpha-1"[tiab] OR "thymosin alpha 1"[tiab] OR "thymosin alpha1"[tiab] OR "thymosin α1"[tiab] OR "thymosin α-1"[tiab] OR "Tα1"[tiab] OR "thymalfasin"[tiab]) AND ("1800/01/01"[edat] : "2026/10/02"[edat]). 0 records; none was a direct comparison of the two compounds.
Related comparisons
BPC-157 vs TB-500
BPC-157 is a 15-residue peptide and TB-500 a seven-residue fragment of Thymosin Beta-4: two different molecules.
Read ComparisonTB-500 vs Thymosin Beta-4
TB-500 is a seven-residue fragment of Thymosin Beta-4; most published research associated with TB-500 used the full 43-residue peptide.
Read ComparisonThymosin Alpha-1 vs Thymosin Beta-4
Thymosin Alpha-1 and Thymosin Beta-4 are different molecules that share part of a name: peptides of 28 and 43 residues.
Read Comparison