What is Semax chemically?

It is a short synthetic peptide built on ACTH(4-10), the fourth to tenth residues of adrenocorticotropic hormone, with a Pro-Gly-Pro tripeptide added at the C-terminus. The ACTH fragment supplies the part of interest and the added tail supplies stability, so the molecule is best read as a stabilised version of a natural hormone fragment rather than as a novel structure.

Why is the Pro-Gly-Pro addition there?

Stability. The bare ACTH(4-10) fragment is degraded quickly by peptidases, which makes it impractical as a research tool however interesting its activity. Proline-containing sequences are comparatively resistant to peptidase cleavage, so appending Pro-Gly-Pro protects the C-terminal end and extends how long the molecule persists intact. It is the same design logic seen in several other modified peptides: keep the active portion, protect the vulnerable end.

Why was an ACTH fragment used as the starting point?

Because ACTH(4-10) had been reported to influence behavioural measures in research models without carrying the hormonal activity of the full-length hormone. Full ACTH stimulates cortisol release, which would confound any study of behavioural or neurological measures; a fragment that retains the measure of interest without the hormonal axis is a cleaner instrument. Whether that separation is as complete as the framing suggests is the kind of question the subsequent literature examines.

What is Semax studied for in research?

The published literature is principally neuroscience, describing effects on measures related to neurotrophic signalling in the models used. As with any such compound, observations depend on the model, the concentration, the exposure and the endpoint, and are properties of those systems rather than general effects.

How strong is the evidence base?

It needs reading with care. The bulk of the published research originates from a single national research programme, much of it in Russian-language or limited-visibility publications, and independent replication by unconnected international groups is limited. Concentrated evidence is weaker than the same volume of work spread across independent groups, because independent replication is how findings get tested. The same caveat applies to the compounds in our [peptide bioregulators](/guides/what-are-peptide-bioregulators) guide.

No. We do not stock it and there is no Certificate of Analysis for it in our library. It is covered here because it draws steady search interest and the limitations of its evidence base are rarely mentioned where it is sold.

What is Semax?

5 min read · Updated October 2026 · MY PEPTIDES Research Team

Key facts

Semax is a synthetic peptide derived from ACTH(4-10), a seven-residue fragment of adrenocorticotropic hormone, with a Pro-Gly-Pro sequence added at the C-terminus. That addition is the design feature: the tripeptide tail substantially increases the molecule\u2019s stability compared with the bare fragment, which would otherwise be degraded rapidly. It was developed in Russian research and is studied in neuroscience contexts, with the published literature describing effects on measures related to neurotrophic signalling in the models examined. Two caveats matter when reading about it. The parent fragment was chosen because ACTH(4-10) had been reported to influence behavioural measures without the hormonal activity of full-length ACTH, and the bulk of the research literature originates from a single national research programme with limited independent international replication. It is not a licensed medicine in the UK. MY PEPTIDES does not stock it. General information for laboratory context only, not medical advice.

The short answer

Semax is a stabilised version of a natural hormone fragment. The core is ACTH(4-10), seven residues taken from adrenocorticotropic hormone, and bolted onto the end is a Pro-Gly-Pro tripeptide whose job is to stop the molecule being degraded.

It was developed in Russian research and is studied in neuroscience contexts. Its evidence base has a specific structural feature that matters more than any individual finding, and that is covered below.

Why build it this way

Two design decisions, each solving a real problem.

Starting from ACTH(4-10) rather than from the whole hormone. Full-length ACTH stimulates cortisol release, which is exactly the sort of thing that ruins an experiment about behaviour or neurological measures: any observation could be attributed to the hormonal axis instead. The fragment had been reported to influence behavioural measures without that hormonal activity, which makes it a cleaner instrument. This is the same selectivity logic that recurs across peptide research, and the same caution applies: a reported separation of activities is a finding to be tested, not a property to be assumed.

Adding Pro-Gly-Pro to the C-terminus. The bare fragment is degraded rapidly by peptidases, which makes it useless as a tool no matter how interesting its activity. Proline-containing sequences resist peptidase cleavage comparatively well, so the tripeptide tail acts as a protective cap. The pattern of keeping an active core and protecting its vulnerable end appears in several compounds documented on this site, and it is one of the most common moves in peptide design.

The result is a molecule that is chemically unremarkable and practically usable, which is the point.

Reading the evidence base

The published literature on Semax is substantial in volume and concentrated in origin. Most of it comes from a single national research programme, a good deal of it appears in Russian-language or limited-visibility publications, and independent replication by unconnected international groups is limited.

This is the same structural issue discussed at length in our guide on peptide bioregulators, and the reasoning is identical. Independent replication is the mechanism by which a scientific claim is tested: findings reproduced by groups with no shared methods, reagents, assumptions or stake have survived a test that findings repeated within one programme have not faced. Volume of publication is therefore a poor proxy for confidence when the publications share an origin.

None of that means the work is wrong. It means the appropriate confidence is lower than the paper count suggests, and a reader who does not know how the literature is distributed will systematically overestimate how well established the compound is.

What the research does not establish

Semax is not a licensed medicine in the UK. Regulatory status differs between jurisdictions, and a compound's status elsewhere does not carry across. Supplying an unlicensed product for human medicinal use is unlawful here under the Human Medicines Regulations 2012 regardless of how a listing is phrased, and our guide on whether peptides are legal in the UK sets out the framework.

Research observations in animal and in-vitro models do not establish effects in humans, and nootropic framing in particular runs well ahead of what the available independent evidence supports.

Where MY PEPTIDES stands

We do not stock Semax. There is no Certificate of Analysis for it in our library and no product page for it on this site, and this guide is not an offer to supply it. What we do supply, and the documentation standard we hold it to, is set out in our guide on certificates of analysis.

The bottom line

Semax is an ACTH(4-10) fragment stabilised with a Pro-Gly-Pro tail, developed in Russian research and studied in neuroscience models. The design is sound and the chemistry unremarkable; the thing to understand is that its literature is concentrated in one research programme with limited independent replication, so confidence should be held more loosely than the volume of publication suggests. It is not a UK-licensed medicine and we do not supply it.

All compounds referenced on this site are discussed strictly in the context of in-vitro laboratory research. Nothing here is a medicine, a supplement, a cosmetic or a therapeutic product, nothing here describes administration or application to humans or animals, and this guide is general information rather than medical, legal or research advice.

Frequently asked questions

What is Semax chemically?: It is a short synthetic peptide built on ACTH(4-10), the fourth to tenth residues of adrenocorticotropic hormone, with a Pro-Gly-Pro tripeptide added at the C-terminus. The ACTH fragment supplies the part of interest and the added tail supplies stability, so the molecule is best read as a stabilised version of a natural hormone fragment rather than as a novel structure.
Why is the Pro-Gly-Pro addition there?: Stability. The bare ACTH(4-10) fragment is degraded quickly by peptidases, which makes it impractical as a research tool however interesting its activity. Proline-containing sequences are comparatively resistant to peptidase cleavage, so appending Pro-Gly-Pro protects the C-terminal end and extends how long the molecule persists intact. It is the same design logic seen in several other modified peptides: keep the active portion, protect the vulnerable end.
Why was an ACTH fragment used as the starting point?: Because ACTH(4-10) had been reported to influence behavioural measures in research models without carrying the hormonal activity of the full-length hormone. Full ACTH stimulates cortisol release, which would confound any study of behavioural or neurological measures; a fragment that retains the measure of interest without the hormonal axis is a cleaner instrument. Whether that separation is as complete as the framing suggests is the kind of question the subsequent literature examines.
What is Semax studied for in research?: The published literature is principally neuroscience, describing effects on measures related to neurotrophic signalling in the models used. As with any such compound, observations depend on the model, the concentration, the exposure and the endpoint, and are properties of those systems rather than general effects.
How strong is the evidence base?: It needs reading with care. The bulk of the published research originates from a single national research programme, much of it in Russian-language or limited-visibility publications, and independent replication by unconnected international groups is limited. Concentrated evidence is weaker than the same volume of work spread across independent groups, because independent replication is how findings get tested. The same caveat applies to the compounds in our [peptide bioregulators](/guides/what-are-peptide-bioregulators) guide.
Do you sell Semax?: No. We do not stock it and there is no Certificate of Analysis for it in our library. It is covered here because it draws steady search interest and the limitations of its evidence base are rarely mentioned where it is sold.