Why study a fragment rather than ACTH itself?

To separate behavioural effects from adrenal steroid release. A fragment too short to drive the endocrine effect isolates the question.

What did the 1970s studies examine?

Short-term memory (Dornbush 1976) and behavioural and physiological measures of attention (Sandman 1977).

Why did Semax follow?

Native ACTH(4-10) degrades rapidly. Semax replaces positions 8 to 10 with Pro-Gly-Pro, a peptidase-resistant motif.

Semax (ACTH Fragment Peptide)

Where This Line of Research Started

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

The behavioural interest in this sequence predates Semax by two decades. Dornbush and colleagues published on ACTH 4-10 and short-term memory in 1976, and Sandman and colleagues on MSH/ACTH 4-10 and measures of attention in 1977.

Key facts

Dornbush 1976: Pharmacol Biochem Behav (PMID 189333)
Sandman 1977: J Clin Endocrinol Metab (PMID 192754)
Fragment studied: ACTH(4-10) itself, not an analogue
Domains examined: Short-term memory, attention
Why a fragment: Separating behaviour from steroid release
Semax came later: As a stabilised analogue

Why anyone tested a fragment of a stress hormone

ACTH's main job is stimulating adrenal steroid release. Observations that it also affected behaviour raised an obvious question: was that a consequence of the steroids, or a direct effect? Testing a fragment too short to drive adrenal stimulation was the way to separate the two, which is why attention turned to residues 4 to 10 specifically.

What the fragment offered

A sequence retaining whatever was behaviourally active while lacking the portions required for the endocrine effect. If a fragment produced behavioural changes without the hormonal ones, the behavioural effect could not be attributed to steroid release. That is a clean experimental logic and it is why this particular fragment became a research object.

Research material referenced

Semax 10mg — third-party HPLC tested

View — £24.99

What was measured

Dornbush and colleagues examined short-term memory in 1976. Sandman and colleagues examined behavioural and physiological measures of attention in 1977, publishing in the Journal of Clinical Endocrinology and Metabolism. Attention and memory are the two domains this literature has concerned itself with ever since.

Why the research did not simply continue

Native ACTH(4-10) is a short unmodified peptide with no protection against peptidases, so its duration is very limited. A fragment that is interesting but degrades almost immediately is difficult to develop further, and that practical obstacle is what later analogue design set out to address.

How Semax relates to that history

Semax retains positions 4 to 7 of the fragment and replaces what followed with Pro-Gly-Pro, a motif chosen for peptidase resistance. It is a response to the durability problem rather than a new pharmacological idea — the question it was built to pursue is the one the 1970s work posed.

How to weigh 1970s behavioural data

Cautiously. Studies from that period generally involved small numbers, and reporting standards for randomisation, blinding and pre-specified endpoints were considerably looser than current expectations. They establish that a question was asked seriously and found interesting; they do not carry the evidential weight a modern trial would.

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

Why study a fragment rather than ACTH itself?: To separate behavioural effects from adrenal steroid release. A fragment too short to drive the endocrine effect isolates the question.
What did the 1970s studies examine?: Short-term memory (Dornbush 1976) and behavioural and physiological measures of attention (Sandman 1977).
Why did Semax follow?: Native ACTH(4-10) degrades rapidly. Semax replaces positions 8 to 10 with Pro-Gly-Pro, a peptidase-resistant motif.

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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