A hormone fragment, with a tail added
Semax is built from a short section of ACTH, the adrenocorticotropic hormone, specifically residues four to seven, with a Pro-Gly-Pro sequence attached at the end. The fragment on its own has no hormonal activity of the kind ACTH is known for.
The added tail is the point: it slows enzymatic breakdown considerably. Without it the fragment would be degraded too quickly to be worth studying.
That tail is a general trick rather than anything specific to this molecule. Proline residues resist several of the peptidases that would otherwise trim a short sequence from its ends, so appending them buys time without disturbing the part of the peptide doing the work. You meet the same manoeuvre across peptide chemistry once you start looking for it.
BDNF, and what the Russian work reports
The mechanism most often cited involves brain-derived neurotrophic factor and related signalling, with reported effects on attention and on outcomes in stroke and ischaemia models. It is registered in Russia for several neurological indications.
The bulk of that literature is Russian-language and was produced under a regulatory framework that differs from the EMA or FDA route. It is not absent evidence, but it has not been through the review process most readers here would assume.
If you searched for what is semax expecting a tidy answer, the regulatory split is why there is not one. The literature indexed on PubMed gives a fair sense of how much of the work is reachable in English and how much is not, which is a more honest measure of the evidence than any summary of its conclusions.
| Length | 7 amino acids |
| Derived from | ACTH fragment 4–7 |
| Modification | Pro-Gly-Pro tail for stability |
| Proposed mechanism | BDNF and related signalling |
| Regulatory status | Registered in Russia; not elsewhere |
| Formats | Peptide pen and nasal spray |
| Purity | ≥ 99% (HPLC) |
| Category | Research use only |
Descriptive data. Read nothing into it about outcomes.
Two formats, one short sequence
Seven residues is short enough for nasal delivery to be worth investigating, which is why semax appears both as a pen and as a spray. The nasal route is the one most of the Russian work used.
Which format suits a given protocol depends on what is being measured. They are alternative routes, not a hierarchy.
Neither format alters what the compound is, and a spray is not a gentler edition of a pen. The nasal spray format page covers what genuinely differs: the preparation itself, the volume delivered per actuation, and the surface the material meets first.
One semax registration, and what it does not carry across
Registration in one country is a real fact about a compound and a weak basis for conclusions anywhere else. It means a national authority reviewed a dossier under its own rules and issued an authorisation. It does not mean another regulator would reach the same view on the same file, and neither the European nor the American authority has been asked to.
For a reader in Europe the practical position is simpler than the regulatory one. There is no marketing authorisation here, which places the compound in the same category as the rest of this catalogue, and what research-only status permits and does not permit is the page that maps where those boundaries actually sit.
The other compound worth reading alongside it is the Dihexa file, which arrives from an entirely different research tradition and shares only the question being asked. Comparing what has been published about each is a quick way to see how differently two compounds in one catalogue area can be evidenced.
Semax in the catalogue
Confirmed at 99% and above by HPLC, with documentation per batch.
Where Semax fits in
The wider frame, in three short pages.
About Semax
What comes up in most enquiries about this compound.