Research-use-only context. This article summarizes published third-party scientific literature — the large majority of it conducted in cultured cells or animal models. It is not medical advice, not a therapeutic or performance claim, and not a usage guide. American Peptides products are sold strictly for in vitro laboratory research and are not for human or veterinary use.
Two different parents, one shared tail
Selank and Semax are frequently listed together, and the reason is structural rather than functional. Both are synthetic heptapeptides built by taking a short endogenous fragment and appending the same three residues — Pro-Gly-Pro — to the C-terminus.
- Selank (CAS 129954-34-3) is Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its parent is tuftsin, an endogenous immunomodulatory tetrapeptide (Thr-Lys-Pro-Arg).
- Semax (CAS 80714-61-0) is Met-Glu-His-Phe-Pro-Gly-Pro. Its parent is the ACTH(4-7) fragment of adrenocorticotropic hormone — a fragment with no corticotropic activity of its own.
The parents are unrelated. The tail is the shared design decision.
What Pro-Gly-Pro is for
Short peptides are degraded rapidly by peptidases, and the C-terminus is a common point of attack. The peptide-chemistry rationale for the Pro-Gly-Pro extension is that proline's constrained ring geometry makes the adjacent bonds poor substrates for many peptidases, so the extended sequence persists longer than the bare parent fragment under the same conditions.
There is direct enzymology on this. A 2001 study examined how both peptides interact with enkephalin-degrading enzymes in human serum — an in-vitro biochemical assay measuring enzyme behaviour in a defined system.1 That is the kind of evidence that supports a stability claim: measurable, mechanistic, and about the molecule rather than about an organism.
What the published research examines
The great majority of the Selank and Semax literature is Russian-language or Russian-origin and uses animal behavioural models. A 2017 study reported behavioural observations in a 6-OHDA rat model,2 and a 2020 paper applied a functional-connectomic approach to studying both peptides in an animal system.3
Two things are worth noting for anyone surveying it. First, these are animal-model studies, and behavioural endpoints in rodents are among the least transferable results in the literature. Second, much of the corpus sits outside the journals and reporting conventions most Western reviewers are calibrated to, which makes independent replication harder to assess rather than absent.
What the research has not established
The honest summary of the Selank and Semax literature is that it is early and largely preclinical. The corpus is dominated by animal behavioural work, and independent replication outside the originating research tradition is limited. Reviewers writing in this area consistently describe the compound as investigational, and it is not approved by the FDA for any use. Findings generated in cultured cells or in animal models do not transfer automatically to any other context, and the gap between a receptor-level observation and a demonstrated outcome in people is the single largest caveat a researcher surveying this literature should carry forward.
Supplied as two separate vials
Where American Peptides lists these together, they are two separately synthesized peptides in their own lyophilized vials — they are not premixed. If the listing includes a spray applicator, the liquid already in the applicator is the supplied reconstitution solution and the peptides remain in their own vials. Each lot is HPLC-characterised with identity confirmed by mass spectrometry and carries its own COA. Full specifications are on the Selank + Semax reference monograph, with single-compound detail at Selank and Semax.
Frequently Asked Questions
Why do Selank and Semax both end in Pro-Gly-Pro?
It is a shared design choice, not a shared origin. The peptide-chemistry literature describes Pro-Gly-Pro as a C-terminal stabilizing motif that slows enzymatic degradation relative to the unextended parent fragment. Their parent sequences — tuftsin and an ACTH fragment — are unrelated.
What are the sequences?
Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro (CAS 129954-34-3). Semax is Met-Glu-His-Phe-Pro-Gly-Pro (CAS 80714-61-0). Both are supplied as lyophilized powders for laboratory research use only.
Are Selank and Semax supplied premixed?
No. They are two separately synthesized peptides in their own vials. Where a spray applicator is included, the liquid in the applicator is the supplied reconstitution solution — the peptides are in separate vials.
Are Selank or Semax approved by the FDA?
No. Neither is approved by the FDA for any indication. Both are supplied strictly as research chemicals for laboratory use only.
References
- In-vitro study of how Semax and Selank interact with enkephalin-degrading enzymes in human serum. Bioorg Khim, 2001. PubMed 11443939
- Behavioural observations with Semax and Selank in a 6-OHDA rat model. Dokl Biol Sci, 2017. PubMed 28702721
- Functional-connectomic approach to studying Selank and Semax effects in an animal model. Dokl Biol Sci, 2020. PubMed 32342318
This article is for laboratory research reference only. American Peptides products are sold strictly for in vitro research. Not for human consumption.
Related research
Compliance Notice: American Peptides products are sold strictly for laboratory and academic research purposes only. They are not intended for human or veterinary consumption, diagnosis, treatment, or prevention of any disease. All content on this page is educational in nature and does not constitute medical advice or product claims. Researchers are responsible for handling these compounds in accordance with their institution’s safety protocols and applicable laws.
