Selank vs Semax: Molecular Differences and Research Evidence

The short answer

Selank and Semax are different molecules built on the same engineering idea. Selank is the immunoglobulin fragment tuftsin extended with Pro-Gly-Pro; Semax is a fragment of adrenocorticotropic hormone extended with the same Pro-Gly-Pro tail ^[6][7]. Beyond that shared tail they have different parent molecules, different sequences and largely separate research literatures.

Most published work studies one compound or the other, which means most of the two bodies of evidence cannot be placed side by side at all. A small number of studies did examine both within the same experiment, and those are the only sources that support a direct comparison. This guide is organised around that distinction: what has actually been compared, and what has not.

Our full single-compound guides are separate: Selank peptide and Semax peptide. Precise Pep Labs sells Selank 10mg and Semax 10mg for in vitro research use only. Nothing here describes or recommends use in people or animals, nothing here is a protocol, and nothing here says that either compound is better than the other for any purpose.

The two molecules side by side

Every identity value above is from the public PubChem record for each compound, and both of our certificates print a formula and CAS number that match those records exactly.

What they share, and what that does not mean

The Pro-Gly-Pro tail is a stability measure. Short peptides are cleaved quickly by peptidases, and a proline-rich tail is intended to slow that. It is a chemical strategy applied to two unrelated starting sequences, not evidence of a shared mechanism.

There is one genuinely shared finding worth stating, because it is supported rather than assumed: for both compounds, published work shows the appended fragment is not biologically inert. In a rat cerebral ischaemia model, Pro-Gly-Pro alone altered transcription of neurotrophins and their receptors, though less selectively than intact Semax ^[13]. In mouse spleen, Selank's short Gly-Pro fragment reproduced much of the parent peptide's gene-expression profile ^[11]. That complicates attribution for both molecules in the same way, and it is the clearest structural parallel between them.

It does not follow that they do the same thing. The parent sequences are unrelated, and the evidence below bears that out.

Studies that examined both compounds

A PubMed search on November 8, 2026 identified five published studies in which Selank and Semax were examined within the same work. These are the only sources that support direct comparative statements.

A placebo-controlled imaging study in healthy volunteers

Panikratova and colleagues assessed resting-state functional connectivity in 52 healthy participants, with regions of interest including the amygdala and the dorsolateral prefrontal cortex in both hemispheres. Resting-state fMRI was performed three times — before, and at two timepoints after, administration of Selank, Semax or placebo. Differences were found between groups and between conditions in connectivity between the right amygdala and a region spanning the fusiform, inferior and middle temporal and parahippocampal gyri in the right hemisphere. The authors stated that post hoc analysis allowed them to define both general and compound-specific effects on that connectivity for the first time ^[1].

This is the strongest comparative source available, and its limits should be stated as plainly as its design. It measured functional connectivity in healthy volunteers. Connectivity is a brain-imaging measure, not a disease endpoint, and the study was not designed to assess one. A difference in a connectivity measure is not a demonstration of benefit, and the study does not establish that either compound is effective for anything.

A side-by-side cell model, with a differential result

Kobylyanskii and colleagues examined several peptides, including Semax and Selank, on proliferation, survival and differentiation of mouse embryonic stem cells and their derivatives. Two results separate the compounds:

• Semax significantly increased the survival rate of mouse embryonic stem cells under serum deprivation.
• Analysis of differentiation into GABA+ neurons showed that Selank reduced the proportion of those cells by 61 % relative to control, an effect shared in that experiment by thyroliberin (58 %) and nerve growth factor (87 %).

The authors' overall conclusion was that the compounds studied do not produce a toxic effect during the embryonic and fetal period of life ^[2].

This is a cell-culture experiment in a mouse model system. It demonstrates that the two compounds behave differently in at least one shared assay; it says nothing about either compound in a person.

A shared animal model, with a largely null result

Slominsky and colleagues tested both peptides in rats with 6-hydroxydopamine-induced parkinsonism. The reported outcome is mostly negative: neither peptide affected motor activity in the elevated cross-shaped maze, and neither affected passive defensive behaviour. Selank decreased the anxiety level of rats with toxic damage to dopaminergic neurons, an effect the authors noted had previously been seen in healthy rodents — leading them to conclude that damage to the substantia nigra does not change the animal's response to that peptide ^[3].

Null results matter in a comparison. In this model, the two compounds were alike in showing no motor effect, and differed only on one anxiety measure.

An independent analysis of marketed material

Vanhee and colleagues at Sciensano, the Belgian national public health institute, analysed two suspicious preparations seized in 2017 and 2018 and identified their contents as Selank and Semax. The paper notes that an online search found these peptides freely available as lyophilised powder or in nasal sprays, and develops a validated LC-MS/MS method — applicable to both hydrophilic and more hydrophobic peptides — for identifying ten such compounds, following the European OMCL network recommendation and validated to ISO 17025 ^[4].

This is the only fully independent source among the five: a national control laboratory with no connection to either compound's developers. It also contains the clearest statement about their trial status, discussed below.

An older comparative pharmacology paper

Liapina and colleagues published a comparison of the anticoagulant effects of regulatory proline-containing oligopeptides, covering glyprolines, Semax and Selank ^[5]. We cite it because it is a genuine head-to-head in an endpoint neither single-compound literature emphasises. The available abstract describes the background and rationale but does not report the comparative results, so we draw no conclusion from it and note it only as evidence that such a comparison exists in the literature.

Where the two literatures cannot be compared

Outside those five studies, placing results side by side is not supportable, for four reasons.

Different primary endpoints. Selank's literature is weighted towards anxiolytic endpoints and the enkephalin-degrading enzyme system ^[10], and towards GABAergic signalling ^[9]. Semax's is weighted towards neurotrophin gene expression and cerebral ischaemia models ^[13]. Most findings in one literature have no counterpart in the other, so there is nothing to compare them against.

Different models even within shared topics. Where both compounds do appear together, the shared endpoint is narrow: one behavioural model, one cell model, one coagulation assay, one imaging protocol.

No established potency or dose equivalence. No source we identified establishes an equivalence between the two compounds in any system, so no statement about one being stronger, faster or more active than the other is supportable.

Contradictions within a single compound's own literature. Selank's GABAergic mechanism, for example, is supported in rat frontal cortex but was not reproduced in a human neuroblastoma cell line, where the compound alone produced no change in GABAergic gene expression ^[12]. A mechanism that is unsettled for one compound cannot be meaningfully ranked against the other.

Marketed product, published human study, and registered trial

These three are different things, and conflating them is the most common error in material about these compounds. Each row below says what a named source or a dated search actually supports, and nothing beyond it.

We searched ClinicalTrials.gov with the registry's own search on November 8, 2026 and again on November 9, 2026, using the single terms "Selank" and "Semax" across all fields ^[16]. "Semax" returned 0 records on both dates. "Selank" returned 10 records on both dates, every one of them unrelated to the peptide and matched on loose text — among them trials of balance exercises, neurofeedback for dyslexia, an antiepileptic drug and hearing aids.

That is one registry and one search strategy, and it should be read as nothing more. ClinicalTrials.gov is the registry maintained by the United States National Library of Medicine. We did not search the Russian State Register of Medicines, the WHO International Clinical Trials Registry Platform, or any other national register, and a study that was never registered anywhere would not appear in any of them. What the search supports is narrow: no study of either peptide is listed on ClinicalTrials.gov on those dates. It is not evidence that no trial of either compound has ever been conducted, completed or registered.

It sits alongside the independent statement in the Sciensano analysis, whose authors wrote that these peptides, "to our knowledge, have not completed any clinical trials" ^[4] — itself a qualified statement rather than a categorical one. It is equally consistent with the existence of published human research on both compounds, such as the 52-participant imaging study described above ^[1], because a study can be conducted and published without ever appearing on that registry.

So these statements sit together without contradiction: both compounds are described in the cited literature as marketed pharmaceutical products in Russia ^[2], both have at least one published study in human participants ^[1], and neither is listed on ClinicalTrials.gov. None of that establishes clinical effectiveness for either compound anywhere, and this guide makes no such claim.

Analytical documentation side by side

Both compounds are covered by a third-party HPLC certificate from the same laboratory, which makes the documentation unusually comparable.

Four observations, none of which favours either compound.

Neither certificate records a lot. Both Batch fields read N/A. The report numbers identify the documents, not the material, and should not be read as verified lot identifiers.

Neither net content can be judged against a criterion. Both certificates print "~10mg" as the reference — a nominal value with no tolerance, upper limit or lower limit anywhere on the document. Both rows are marked by the laboratory as meeting that reference. Because no numeric acceptance range is documented, the size of either difference cannot be assessed against a criterion, and this guide does not describe either result as passing or failing. Our guide to purity versus net content explains why the two measurements answer different questions.

Neither identity line prints an observed mass. For both compounds that gap matters specifically, because each is also sold in an acetylated form. For Semax, published chemistry shows the acetylated variant forms a different copper complex and did not reproduce the unmodified peptide's protection in a cell model ^[14]. An intact-mass measurement would separate the forms; a confirmation line without one cannot. Our guide to reading a certificate of analysis covers what each field does and does not establish.

Endotoxin is excluded for both. Neither this guide nor our single-compound guides present an endotoxin result for Selank or Semax. Our editorial review of the available endotoxin documentation is unresolved, and endotoxin is in any case a separate measurement from chromatographic purity: a purity percentage says nothing about endotoxin content, and the reverse is equally true.

Limitations and open questions

• Only five studies examined both compounds, and one of them ^[5] reports no comparative results in its available abstract.
• The strongest comparative study measured connectivity, not outcomes, in healthy volunteers ^[1].
• The shared animal model was largely null for both compounds on motor endpoints ^[3].
• Both literatures are institutionally concentrated, with the Sciensano analysis ^[4] the clearest independent exception across either.
• No potency or equivalence relationship is established between them in any source.
• Neither certificate records a lot identifier or an observed mass, so neither supports a lot-level identity claim.
• The registry check covers one registry. The ClinicalTrials.gov searches above describe what is and is not listed there on the dates given. They say nothing about the Russian State Register, the WHO registry platform, or any study that was never registered.
• Sources read. Findings were verified against published abstracts and bibliographic records through PubMed, identity values against PubChem, and the registry statement against a ClinicalTrials.gov search on the date given. Full texts were not obtained for this article, so results reported only in figures or supplementary material are not represented here.

Where to find the certificates

Both Kovera Labs reports are in our COA Library, and each is linked from its product page: Selank 10mg and Semax 10mg. If the lot printed on a vial you hold does not appear there, contact us with that lot number and we will locate the corresponding report.