Semax and Selank: Identity and Evidence Differences

What each compound is

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro (about 813.9 Da). It corresponds to the ACTH(4-10) fragment of adrenocorticotropic hormone with a Pro-Gly-Pro extension at the C-terminus. The extension is a design feature intended to slow breakdown. Our Semax research overview covers its evidence in more detail.

Selank is also a synthetic heptapeptide, with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro (about 751.9 Da). It is built on tuftsin, the tetrapeptide Thr-Lys-Pro-Arg, and carries the same Pro-Gly-Pro extension.

Where they differ

Both were developed in Russia and are described in the Russian literature as pharmaceutical products. Neither is a licensed medicine in the United Kingdom, and the materials supplied here are laboratory reagents.

Mass is a practical identifier here. The two differ by roughly 62 Da, so a certificate reporting a mass far from the expected value is describing a different material rather than a variation of the one listed.

Where the comparison breaks down

The two are paired in retail listings, but the pairing is conventional. They share a C-terminal Pro-Gly-Pro extension and a country of origin. They do not share a parent molecule, and no common documented target makes one a version of the other.

Evidence is also not comparable. Each compound's published record comes from a small number of research groups, mostly in rodent and cell models, and we are not aware of a head-to-head study. Findings for one cannot be used to rank the other, and no table in this article can supply a ranking the literature does not contain.

A large share of the primary literature for both appears in Russian journals, many of them in English translation. Study designs, animal strains and reporting conventions differ from study to study, which makes cross-study comparison harder still.

What a fair comparison can cover

A comparison is legitimate on questions that have documentary answers: sequence, parent molecule, mass, supplied format and what each batch certificate reports. It is not legitimate on questions that need head-to-head data, such as relative performance, tolerability or suitability for a given purpose. Where a page ranks the two on those, it is presenting a preference as a finding.

Common conflations

• •"Which is stronger." The question assumes a shared scale. The compounds are structurally unrelated, so there is no common measure to be stronger on.
• •"Nootropic." In retail copy this is a marketing label applied to both. It is not a pharmacological class and does not describe a demonstrated outcome.
• •N-acetyl forms. N-acetyl versions of each are separate molecules with different masses, not alternate names for the compounds above.
• •Pen and nasal-spray listings. These are other supply formats. The items compared here are single-compound lyophilised vials.

Analytical documentation

Each certificate reports identity and measured purity for the batch tested, and nothing about biological effect. Published reports are in the COA library; the product records are Semax 10mg and Selank 10mg, and both sit in the nootropic category.

The guides to reading a peptide COA and understanding HPLC purity explain what those documents can and cannot show. Buying guides are available for Semax and Selank.

Scope and laboratory-use boundary

Materials sold on this site are supplied solely for non-clinical in-vitro laboratory research. They must not be ingested, injected, inhaled, applied or otherwise administered to a human or animal.

We do not provide dosing, routes of administration, treatment guidance, cosmetic-use guidance or in-vivo protocols. Preparation, storage and handling must follow a validated institutional SOP, the material documentation and an appropriate risk assessment.