What is each one, chemically?
Thymosin alpha-1 is one defined 28-amino-acid peptide. Thymalin is a mixture of peptides extracted from calf thymus, so its composition varies by preparation and mechanism claims can only apply to the mixture.
Summary
Thymosin alpha-1 is a single defined molecule with international approvals and a label schedule; thymalin is a thymus-extract mixture whose evidence is old, regional, and low-certainty.
Key answers
Which has real evidence?
Thymosin alpha-1 has the stronger record: approved in dozens of countries (as Zadaxin) with label-defined schedules. Thymalin's support is a 266-person geriatric cohort and decades-old regional literature, with no confirmatory modern trials.
What is the identity risk?
Gray-market thymalin listings sometimes sell single-sequence peptides under the extract's name, which breaks the lineage's evidence entirely. With thymosin alpha-1 the identity question is simpler because the molecule is defined.
Comparison matrix
| Dimension | Thymalin | Thymosin alpha-1 |
|---|---|---|
| Overall evidence grade | D | C |
| Evidence label | Limited human evidence | Limited human evidence |
| Regulatory status | Varies by product and jurisdiction | Varies by product and jurisdiction |
| Editorial confidence | Low confidence | Moderate confidence |
| Efficacy | 0/5 not mapped | 2/5 limited |
| Safety | 0/5 not mapped | 2/5 limited |
| Regulatory risk | 3/5 moderate | 4/5 high |
| Product quality risk | 3/5 moderate | 4/5 high |
| Primary claim categories | Immune and inflammation | Immune modulation, Chronic hepatitis B evidence, Sepsis evidence, COVID and vaccine-response claims, FDA compounding review |
Peptide summaries
0/5 efficacy
Thymalin
Legacy Russian immune preparation with old, low-quality human literature.
Varies by product and jurisdiction
2/5 efficacyThymosin alpha-1
Thymosin alpha-1 has to be judged by clinical setting: chronic hepatitis B has the clearest historical positive signal, sepsis has a modern non-confirmatory phase 3 result, COVID and vaccine-response evidence is mixed or selected, and clinic wellness claims need direct evidence.
Varies by product and jurisdiction
References
- 1.
FDA. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee 2026.
Accessed 2026-07-24.
FDA meeting page for the July 23-24, 2026 PCAC review of BPC-157, KPV, TB-500, MOTs-C, emideltide/DSIP, Semax, and Epitalon bulk substances, including the uses evaluated for each, briefing documents, and docket FDA-2025-N-6895.
- 2.
FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks 2026.
Accessed 2026-06-08.
FDA summarizes potential significant safety risks and missing safety information for several nominated peptide bulk substances.