So is 'ACTH(4-10) analogue' wrong?

Not wrong, but imprecise. It describes design lineage. Structurally Semax shares only residues 4–7 with ACTH.

Why does Semax not stimulate the adrenals?

The Arg-Trp-Gly segment that contributes to that activity is not present. Pro-Gly-Pro replaces it.

Does the literature use both names?

Yes. Paper titles commonly say ACTH(4-10) analogue; PubChem indexes the structure as ACTH(4-7)-PGP.

Semax (ACTH Fragment Peptide)

Is Semax Really an ACTH(4-10) Analogue?

JMWritten & reviewed by Jack Muncaster · Founder, UK PeptidesLast reviewed 2026-08-232 cited sources

Semax is conventionally described as an ACTH(4-10) analogue, and peer-reviewed papers use that phrase. Structurally it shares only residues 4 to 7 with ACTH — Met-Glu-His-Phe — with Pro-Gly-Pro replacing rather than modifying Arg-Trp-Gly. PubChem indexes it as ACTH(4-7)-PGP.

Key facts

ACTH(4-10) sequence: Met-Glu-His-Phe-Arg-Trp-Gly
Semax sequence: Met-Glu-His-Phe-Pro-Gly-Pro
Shared with ACTH: Residues 4–7 only
Replaced: Arg-Trp-Gly → Pro-Gly-Pro
PubChem indexing: ACTH (4-7), Pro-Gly-Pro-
Consequence: No steroidogenic activity

Line the two sequences up

ACTH residues 4 through 10 are Met-Glu-His-Phe-Arg-Trp-Gly. Semax is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues are identical. The last three are entirely different — not conservative substitutions, but a replacement of arginine, tryptophan and glycine with a proline-glycine-proline motif. Both peptides are seven residues long, which is part of why the ACTH(4-10) description became conventional.

Why the conventional name persists

It is not an error so much as a shorthand describing lineage rather than composition. Semax was designed from the ACTH(4-10) region, and papers including the 2006 Brain Research study on BDNF and trkB expression carry 'an analog of ACTH(4-10)' in their titles. PubChem, which indexes by structure rather than design history, records it as ACTH(4-7) plus Pro-Gly-Pro. Both descriptions are in legitimate use.

Research material referenced

Semax 10mg — third-party HPLC tested

View — £24.99

Why the distinction actually matters

Because the substituted residues are the functionally important ones. The Arg-Trp-Gly segment contributes to ACTH's melanocortin-receptor pharmacology and its adrenal-stimulating activity. Removing it is not incidental tidying — it is the deliberate step that yields a peptide retaining reported central activity without stimulating adrenal steroidogenesis. Describing Semax as an ACTH(4-10) analogue and stopping there obscures the single most consequential design decision in the molecule.

What Pro-Gly-Pro brings in its place

Proline-containing motifs resist most peptidases, because the ring structure constrains the backbone conformation that proteolytic enzymes require at their active site. Substituting a protease-vulnerable tripeptide with a proline-rich one raises stability substantially. So the same change that removes an unwanted activity also solves a durability problem, which is an unusually economical piece of design.

How to describe it precisely

The accurate short description is that Semax is a heptapeptide comprising the ACTH(4-7) fragment with a C-terminal Pro-Gly-Pro extension. If reading a paper that says ACTH(4-10) analogue, nothing is wrong — but the reader should know the two peptides diverge after residue four.

Quick reference

Position	ACTH(4-10)	Semax
1 (ACTH 4)	Met	Met
2 (ACTH 5)	Glu	Glu
3 (ACTH 6)	His	His
4 (ACTH 7)	Phe	Phe
5	Arg	Pro
6	Trp	Gly
7	Gly	Pro

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

So is 'ACTH(4-10) analogue' wrong?: Not wrong, but imprecise. It describes design lineage. Structurally Semax shares only residues 4–7 with ACTH.
Why does Semax not stimulate the adrenals?: The Arg-Trp-Gly segment that contributes to that activity is not present. Pro-Gly-Pro replaces it.
Does the literature use both names?: Yes. Paper titles commonly say ACTH(4-10) analogue; PubChem indexes the structure as ACTH(4-7)-PGP.

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.

How we write and check this content Report a factual error in this article

More Semax (ACTH Fragment Peptide) articles

Popular across the research hub

One flagship guide from every other research category — keep exploring.

← Back to Forum