Semax is a synthetic seven-residue peptide built from a fragment of adrenocorticotropic hormone with the hormonal activity engineered out and a short stabilising tail added. Developed in Russia and still prescribed there, it has an unusual research profile: a substantial clinical literature in one language and comparatively little independent replication outside it.
What is Semax?
Semax is a heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues — Met-Glu-His-Phe — are the ACTH(4–7) fragment of adrenocorticotropic hormone, taken unchanged. The final three, Pro-Gly-Pro, are a synthetic addition that does not occur in the hormone at all. You will also see Semax described as an analogue of the longer ACTH(4–10) fragment, because the Pro-Gly-Pro tail stands in for the three residues that would otherwise follow; both descriptions refer to the same molecule, and “ACTH(4–7)-Pro-Gly-Pro” is the more literal of the two.
That construction is the whole point of the molecule, and it is worth understanding before reading anything else about it. ACTH is a hormone whose primary role is stimulating cortisol release from the adrenal cortex. Researchers studying it had long observed that certain fragments appeared to influence behaviour and learning in animal models independently of the hormonal cascade. The problem was separating the two: anything retaining corticotropic activity would flood the system with downstream hormonal effects that made the behavioural question impossible to isolate.
Semax was engineered to resolve that. It retains the short central fragment associated with the neural observations while lacking the structural elements required for corticotropic activity, so it does not stimulate cortisol release. It is, in effect, an attempt to keep one property of a hormone and discard the rest.
It was developed in Russia and remains a prescription medicine there, listed among the country's essential medicines. It has not been evaluated or approved in most other jurisdictions, including Canada.
| Common name | Semax |
|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro |
| Single-letter code | MEHFPGP |
| Residue count | 7 amino acids (heptapeptide) |
| Derived from | ACTH(4–7) fragment (Met-Glu-His-Phe) plus a synthetic Pro-Gly-Pro extension; also written ACTH(4–10) analogue |
| Molecular formula | C37H51N9O10S |
| Molecular weight | 813.93 g/mol |
| CAS number | 80714-61-0 |
| Corticotropic activity | None reported — the hormonal action of the parent fragment is absent |
| Physical form | Lyophilised powder |
| Format supplied | 10 mg per vial |
| Purity standard | ≥99%, verified by HPLC and mass spectrometry |
| Classification | Neuro research compound |
The Pro-Gly-Pro tail and why it matters
The three residues appended to the ACTH fragment are not decorative. Short peptides are ordinarily degraded within minutes by peptidases, which is the central practical obstacle to studying them: a compound that disappears before it can act is difficult to characterise regardless of what it might do.
Proline is comparatively resistant to cleavage by many peptidases, owing to its unusual ring structure, which constrains the backbone geometry that those enzymes require. A proline-containing tail at the terminus therefore slows degradation of the whole molecule considerably. The Pro-Gly-Pro motif is a recurring design element in this family of Russian-developed peptides for exactly that reason — it appears again in Selank, which applies the same approach to a different parent sequence.
For anyone working with these compounds, that shared design is more informative than it first appears: it means Semax and Selank are not two unrelated molecules that happen to come from the same country, but two applications of one stabilisation strategy.
Reported mechanisms
The honest position is that the mechanism is not established. Published sources describing Semax generally state outright that its mode of action remains unknown, and the candidate mechanisms in the literature should be read as hypotheses with varying levels of support rather than as settled pharmacology.
The most frequently reported observation is an effect on neurotrophins. Animal studies describe Semax rapidly raising levels and expression of brain-derived neurotrophic factor and its receptor TrkB in the hippocampus. BDNF is central to synaptic plasticity, and a compound that moves it quickly is of obvious interest, but the finding describes an effect rather than a mechanism — it does not explain what the peptide binds in order to produce it.
Two further candidates appear regularly. Semax may interact with melanocortin receptors, which would be consistent with its ACTH origin, since ACTH is itself a melanocortin-family peptide. It has also been proposed to inhibit enkephalinase enzymes, which would indirectly raise levels of endogenous opioid peptides. Neither is firmly established.
Reading the Semax literature: a large proportion of the published work is Russian-language, produced in the context of a domestic approved medicine, and has not been independently replicated in Western laboratories. That is not an accusation — it reflects where the compound was developed and regulated — but it does mean the evidence base is structurally different from that of a compound studied in parallel across multiple research communities. Anyone evaluating this literature should note which claims rest on independently replicated work and which rest on a single national research tradition, and should be particularly cautious with secondary English-language summaries, which frequently restate Russian clinical findings without that context.
Research contexts
Published work involving Semax clusters around neuropeptide signalling, neurotrophin expression, and models of cognitive and neurological function. In our catalogue it sits under neuro research, alongside the other compounds studied in nervous-system model systems.
It is also used straightforwardly as a reference peptide in analytical work — a defined seven-residue sequence with a known mass is useful for validating detection methods, and the proline-rich tail makes it a convenient test case for studying peptidase resistance itself.
Researchers comparing Semax against structurally related compounds commonly work with Selank in parallel, and the Semax and Selank blend exists for studies running both. If you are new to multi-compound formulations, our guide to peptide blends covers how they are put together and when a blend is or is not appropriate for a controlled experiment.
Regulatory status
Semax is a prescription drug in Russia and appears on that country's list of vital and essential medicines. It is not approved by the FDA, and in the United States it is unscheduled but unapproved. It has not been evaluated or authorised in most other countries.
Handling and storage in the laboratory
Semax is supplied as a lyophilised powder, comparatively stable in that form under cold storage and markedly less so once reconstituted. Standard practice is to keep sealed vials frozen and protected from light and moisture, and to let a vial reach room temperature before opening so that atmospheric moisture does not condense inside it.
One sequence-specific point: Semax begins with methionine, and methionine is among the residues most readily oxidised. An N-terminal methionine is particularly exposed, so minimising air contact during handling matters more for this peptide than for sequences lacking it. Oxidation produces a species with a different mass, which means it is detectable by mass spectrometry — useful if you are troubleshooting unexpected results.
Reconstitution solvent, working concentration and aliquoting strategy depend on the assay and should follow the protocol of the study being run rather than any general figure. Avoid repeated freeze-thaw cycling, which is the single most common avoidable source of variation between runs, and record lot numbers against experiments so that a batch change does not become an undiagnosable confound later in a series.
Verification and certificates of analysis
A purity figure means little without the document behind it, and in this market certificates are often generic, undated, or produced only after purchase. Every Semax lot NexPept lists is tested by an independent third-party laboratory using high-performance liquid chromatography and mass spectrometry, and the report is published openly.
Reports for every batch we have shipped are in the NexPept Certificate of Analysis library, with the batch number printed on each vial matching a published certificate. From late September 2026 onward we have also been adding heavy-metal and endotoxin testing to those reports.
When reading any certificate, confirm that the batch number matches the vial you received, that both an identity method and a purity method are reported rather than purity alone, that the test date is recent, and that the issuing laboratory is named. Our quality standards page sets out how our batches are tested and documented, what research peptides are explains how research-grade material differs from a drug or a supplement, and our guide to research peptides in Canada covers sourcing and regulation in more depth. If you are weighing suppliers, buying peptides in Canada walks through what to check before ordering.
Lyophilised powder, batch-tracked, third-party tested by HPLC and MS. Ships from Ontario with same-day dispatch on orders placed before 2 PM EST.
View Semax 10 mg See the COARelated research compounds
Researchers working on neuropeptide questions frequently hold these alongside Semax — Selank as the closest structural relative, the blend for studies running both, and the remaining neuro-category compounds for adjacent model systems:
Frequently asked questions
What is Semax derived from?
The ACTH(4–7) fragment of adrenocorticotropic hormone — Met-Glu-His-Phe — with a synthetic Pro-Gly-Pro tail added at the C-terminus. It is also commonly written as an ACTH(4–10) analogue. The full sequence is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues come from the hormone; the last three do not occur in it.
Does Semax have hormonal activity like ACTH?
No. ACTH's defining action is stimulating cortisol release from the adrenal cortex, and Semax does not retain that activity. Separating the fragment from the hormonal cascade was the specific design goal, because the hormonal effects otherwise make the neural observations impossible to study in isolation.
Why does the Pro-Gly-Pro tail matter?
It slows enzymatic degradation. Proline's ring structure constrains the peptide backbone in a way that many peptidases cannot accommodate, so a proline-containing terminus extends how long the molecule survives. The same motif appears in Selank, which uses the same stabilisation strategy on a different parent sequence.
How does Semax work?
Not established. Published sources state the mechanism is unknown. Animal studies report rapid increases in BDNF and its TrkB receptor in the hippocampus; proposed interactions with melanocortin receptors and inhibition of enkephalinase enzymes have also been suggested. All should be treated as hypotheses rather than settled pharmacology.
Semax or Selank — what's the difference?
Different parent sequences sharing a design principle. Semax is built from an ACTH fragment; Selank from a different endogenous peptide. Both carry a Pro-Gly-Pro extension for peptidase resistance and both came out of the same Russian research tradition, which is why they are frequently studied in parallel. We also list them together as a combined blend.
Is Semax approved in Canada?
No. Semax is a prescription medicine in Russia and is on that country's essential medicines list, but it has no Health Canada authorisation and is not FDA approved. Research-grade material supplied by NexPept is not a drug, supplement or treatment, and is for laboratory research use only.
What purity should I expect, and how is it verified?
NexPept lists Semax at ≥99% purity, confirmed by HPLC and mass spectrometry before a lot is listed. Reports for every batch we have shipped are published in our COA library, so the certificate is available before you order rather than after.
How should Semax be stored and handled?
Sealed vials kept frozen, protected from light and moisture, and brought to room temperature before opening so moisture does not condense inside. This sequence has an N-terminal methionine, which oxidises readily, so minimising air exposure matters more here than for many peptides. Specific conditions should follow the protocol being run.
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More from NexPept: browse the full research catalogue, read our other research articles, or check the frequently asked questions for ordering and documentation details.