Are Semax and Selank the same class of peptide?

They share a design approach and a stabilising motif, but their bioactive fragments come from unrelated parent peptides — ACTH and tuftsin.

Does the Pro-Gly-Pro make them act similarly?

No. It is a stabilisation device rather than the source of activity; the pharmacophore in each sits in the retained fragment.

Is either approved in the West?

Neither. Both hold Russian registration histories and no MHRA, EMA or FDA authorisation.

Semax (ACTH Fragment Peptide)

Semax vs Selank: How They Differ

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-233 cited sources

Both were developed at the Institute of Molecular Genetics of the Russian Academy of Sciences and both use a Pro-Gly-Pro extension for stability, but their bioactive fragments come from unrelated parent peptides: Semax from ACTH, Selank from tuftsin, an immunomodulatory fragment of immunoglobulin G.

Key facts

Semax parent: ACTH (adrenocorticotropic hormone)
Selank parent: Tuftsin (IgG-derived tetrapeptide)
Shared design feature: Pro-Gly-Pro extension
Common origin: Institute of Molecular Genetics, RAS
Semax PubMed records: ~231
Selank PubMed records: ~135
Western approval: Neither

The same design philosophy, different starting material

Both peptides follow one strategy: take a short bioactive fragment of a larger endogenous peptide, append Pro-Gly-Pro to make it durable. What differs is the fragment. Semax starts from ACTH, a pituitary hormone. Selank starts from tuftsin, a tetrapeptide derived from the Fc region of immunoglobulin G with described immunomodulatory activity. Those parents have nothing to do with one another.

Why the shared motif does not make them similar

It is easy to read 'both use Pro-Gly-Pro' as implying a family relationship. It does not. The extension is a stabilisation device, not the source of activity — the design assumption in both cases is that the pharmacophore sits in the retained fragment. Two peptides sharing a stabilising tail are no more related than two proteins sharing a purification tag.

Research material referenced

Semax 10mg — third-party HPLC tested

View — £24.99

Different research literatures

Semax's literature centres on neurotrophin expression, neuroprotection in ischaemia models and cognition, with roughly 231 indexed records. Selank's centres on anxiolytic and immunomodulatory activity, consistent with its tuftsin origin, with roughly 135. Both share the pattern of internationally published preclinical work alongside clinical literature concentrated in Russian-language journals.

What tuftsin is

Tuftsin is a tetrapeptide, Thr-Lys-Pro-Arg, released from the heavy chain of immunoglobulin G. It was described as stimulating phagocytic activity in macrophages and neutrophils, which is why Selank's reported activity profile leans immunomodulatory in a way Semax's does not.

Shared regulatory position

Neither holds a marketing authorisation from the MHRA, EMA or FDA. Both have Russian registration histories. Both are supplied here for laboratory research only, and the same distinction applies to each: a registration elsewhere is a fact about another regulator's decision, not a therapeutic claim we make.

Quick reference

	Semax	Selank
Parent peptide	ACTH	Tuftsin (IgG-derived)
Bioactive fragment	ACTH(4-7)	Tuftsin
Stabilising motif	Pro-Gly-Pro	Pro-Gly-Pro
Research emphasis	Neurotrophins, ischaemia	Anxiolytic, immunomodulatory
PubMed records	~231	~135
Western approval	None	None

Extended research context

The Semax (ACTH Fragment Peptide) deep dive

Deep dive: what the Pro-Gly-Pro extension actually accomplishes

Semax is built from a four-residue fragment of ACTH with Pro-Gly-Pro appended, and that appendix does two separate jobs at once. Proline is the only proteinogenic amino acid whose side chain bonds back to its own backbone nitrogen, forming a ring that removes the amide hydrogen and locks rotation. Proteolytic enzymes generally need an extended, rotatable backbone at their active site, so bonds near proline are poor substrates for most of them — which is why proline-rich motifs recur throughout stabilised peptide design. The second job is subtractive: Pro-Gly-Pro occupies the positions where ACTH carries Arg-Trp-Gly, and those are the residues contributing to the parent hormone's adrenal-stimulating activity. One substitution therefore buys protease resistance and removes an unwanted pharmacology, which is unusually economical design.

Deep dive: the naming point worth getting right

Semax is near-universally described as an ACTH(4-10) analogue, and peer-reviewed paper titles use that phrase. Structurally it is not quite that. ACTH residues 4 to 10 are Met-Glu-His-Phe-Arg-Trp-Gly; Semax is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues match and the last three are wholly different — replacement rather than modification. PubChem, indexing by structure rather than design lineage, records it as ACTH(4-7) plus Pro-Gly-Pro. Neither name is wrong, but the loose one obscures the fact that the substituted segment is precisely the functionally consequential part.

Deep dive: reading an unevenly distributed evidence base

Semax's roughly 231 indexed records split along an unusual line. Mechanistic work — BDNF and trkB expression in rat hippocampus, transcriptomics in focal cerebral ischaemia, neurotrophin dynamics across brain regions — appears in international journals in English and can be assessed directly. Clinical work is concentrated in Russian-language publications, principally the Korsakov Journal of Neurology and Psychiatry, indexed by translated title and often without accessible English full text, much of it predating current standards for pre-registration and reporting. The honest position is that this is evidence which is difficult to verify independently, which is a different thing from evidence that is absent, and a different thing again from evidence that is established.

Research applications

▸Neurotrophin expression research (BDNF, NGF, TrkB, TrkA)
▸Neuroprotection and cerebral ischaemia models
▸Study of proline-stabilised peptide design
▸Comparative work on ACTH fragments without steroidogenic activity
▸Transcriptomic profiling in rodent brain models

Handling checklist

✓Store lyophilised material cold, dry and protected from light
✓Expect methionine oxidation as the degradation route (+16 Da; only one Met, so not +32)
✓No reducing agent needed — the sequence contains no cysteine
✓Introduce diluent gently against the vial wall; swirl rather than shake
✓Aliquot to avoid repeated freeze-thaw cycles
✓Check whether a certificate reports net peptide content or gross salt weight

Common research-handling mistakes

Learnt from thousands of researcher orders across our UK labs.

✗ Describing Semax as ACTH(4-10) without qualification

Fix: It shares only residues 4-7; Pro-Gly-Pro replaces Arg-Trp-Gly, and that replacement is the design's whole point.

✗ Treating Russian registration as equivalent to MHRA approval

Fix: Authorisations are jurisdictional and do not transfer. Semax has never been assessed by the MHRA, EMA or FDA.

✗ Reading a BDNF expression change as a demonstrated outcome

Fix: The studies measured gene and protein expression in rats. Expression is upstream of function and upstream again of any clinical claim.

✗ Assuming a named receptor exists

Fix: No primary receptor has been definitively established; the literature characterises downstream effects more confidently than the initiating event.

✗ Expecting ACTH-like adrenal effects

Fix: Semax does not stimulate adrenal steroidogenesis — the responsible residues were substituted out.

Continue researching

Peer-reviewed guides, comparators and matched reference materials.

Frequently asked questions

Are Semax and Selank the same class of peptide?: They share a design approach and a stabilising motif, but their bioactive fragments come from unrelated parent peptides — ACTH and tuftsin.
Does the Pro-Gly-Pro make them act similarly?: No. It is a stabilisation device rather than the source of activity; the pharmacophore in each sits in the retained fragment.
Is either approved in the West?: Neither. Both hold Russian registration histories and no MHRA, EMA or FDA authorisation.

Primary sources & clinical trials

Peer-reviewed research and registered trials from PubMed, ClinicalTrials.gov, PubChem, FDA and NIH. All links open in a new tab and point to the primary source, so every claim can be verified at origin.

Written and reviewed by

Jack Muncaster · Founder, UK Peptides

Jack founded UK Peptides in Manchester after repeatedly receiving research compounds with missing or recycled paperwork. He is responsible for supplier selection, batch release decisions and the content published in this research library. Every article here is sourced to primary literature and every product page to a signed third-party certificate.

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