Semax vs Selank: What Is the Difference?

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What Is the Difference Between Semax and Selank?

Semax and Selank differ in their first four amino acids, and in nothing else structurally. Both chains are seven residues long, and both end in the same Pro-Gly-Pro tail. Semax opens with a fragment of a hormone; Selank opens with a naturally occurring peptide called tuftsin.

That is a larger difference than it sounds. Four of seven positions is most of the molecule, and the two sets of four share no amino acid at all. The result is two compounds with different molecular formulas, different masses and separate research literatures.

Are Semax and Selank the Same Peptide?

No. Semax and Selank are separate compounds with separate chemical database entries, separate molecular formulas and separate masses. They are not two names for one substance, and they are not two strengths of one substance.

The confusion is understandable, because both are heptapeptides — chains of seven amino acids — and the two are almost always described together. But sharing a length is not sharing an identity. The first four positions have no overlap whatsoever: methionine, glutamate, histidine and phenylalanine against threonine, lysine, proline and arginine.

What Is Semax?

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. Its first four amino acids are positions 4 to 7 of adrenocorticotropic hormone, usually shortened to ACTH. The closing Pro-Gly-Pro is added in the laboratory, and the hormone itself does not carry it.

The published work sits mostly in one field: gene-transcription measurement in rat cortical tissue. A 2010 study reported changes in the transcription of genes for several neurotrophins and their receptors in that tissue. Transcription is the step where a gene is read out into the message a cell uses to build a protein, and the study measured that step and nothing beyond it.

A 2017 genome-wide study in the same rat model reported that the gene sets with the largest transcript-level changes were those for antigen presentation and interferon signalling. Both findings are animal data, and both measure gene activity rather than behaviour. The Semax listing carries the full sequence, the vial strengths and its own research answers.

What Is Selank?

Selank is a synthetic heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its first four amino acids are the sequence of tuftsin, a naturally occurring four-amino-acid peptide. The same Pro-Gly-Pro tail closes the chain. Published papers also file the compound under the code TP-7.

Its research literature points somewhere else entirely. A 2016 study measured a panel of 84 genes involved in neurotransmission in the frontal cortex of rats, and compared the expression pattern recorded for Selank with the pattern recorded for GABA. The two patterns correlated positively at the earlier of the two time points the study sampled.

The authors of that study proposed allosteric modulation of the GABAergic system as one possible mechanism. Allosteric means binding somewhere other than the site the ordinary signal uses, and altering how the receptor responds. That is a proposal drawn from gene expression in rats, not a measured receptor result. The Selank listing carries the sequence and the vial it is supplied in.

What Do Semax and Selank Have in Common?

Semax and Selank share three things: seven amino acids each, the same Pro-Gly-Pro ending, and most of the same authors. Everything else in their published records differs — the model systems, the measurements taken, and the research fields the work belongs to.

The shared tail is not decoration, and one study examined it directly. The 2010 rat work included Pro-Gly-Pro on its own as a third arm, and recorded transcription changes across several of the same genes. The two profiles overlapped only partly: the pattern recorded for Semax was described as region-selective, while the pattern recorded for the tripeptide was described as mainly unspecific.

Has Semax Been Compared Directly With Selank?

Yes, but only twice and only narrowly. Two published studies put Semax and Selank into the same experiment: an enzyme assay from 2001 and a brain-imaging study from 2020. Neither measured an outcome, and neither compares the two on anything a buyer would call a result.

The enzyme assay, 2001. Both peptides inhibited enkephalin-degrading enzymes taken from human serum, and both did so in a concentration-dependent way. This was done in glassware, not in a living subject, and it is an enzyme-chemistry observation rather than a measure of what either compound does. In the same assay their five-amino-acid fragments were active too; the three-, four- and six-amino-acid fragments were not.

The imaging study, 2020. The second study to place both compounds in one experiment used resting-state functional MRI, a scan that measures connectivity between brain regions while no task is performed. It is an imaging measurement rather than an outcome measurement, and it settles nothing about what either compound does — which is the point worth carrying away from it.

That is the entire direct comparison. Away from those two experiments the published record on each peptide runs on its own track, in in-vitro assays and in animal models, and nothing in the literature joins the two ends together.

Do Semax and Selank Work by the Same Mechanism?

The published evidence does not support reducing either peptide to a single mechanism, and it does not show the two sharing one. What it shows is two separate measurement programmes that intersect in exactly one in-vitro assay.

The intersection is real: both inhibited the same serum enzymes in 2001, and the authors suggested this may be one basis for the biological activity of each. Away from that assay the records point in different directions. Semax’s rat work centres on neurotrophin and immune-response gene transcription; Selank’s on neurotransmission gene expression and a proposed GABAergic link.

The shared tail complicates the picture rather than simplifying it. Because Pro-Gly-Pro alone changed gene transcription in the 2010 rat study, any effect common to both peptides could belong to the tail instead of to either compound. No study opened for this page separates those possibilities.

Is Semax the Same as N-Acetyl Semax Amidate?

No. N-acetyl semax amidate is a modified analogue of Semax with its own chemical identity, its own database record and a different molecular formula. An analogue is a molecule built on the structure of another, and it is not interchangeable with the original.

Two changes separate them. An acetyl group is attached at the front of the chain, and the acid group at the far end is converted to an amide. That moves the formula from C37H51N9O10S at 813.9 g/mol to C39H54N10O10S at 855.0 g/mol.

The consequence for reading research is direct: a study of Semax is not automatically a study of the acetylated form. Australian Research Peptides lists Semax itself under Neuropeptide Research, and the acetylated analogue is not that listing.

Does “Selank Acetate” Mean a Different Sequence?

No. Selank acetate names the salt the peptide is supplied as, not a different sequence. The seven amino acids are identical. Chemical databases hold the acetate as a record of its own, because the added acetate changes the formula and the mass while leaving the sequence untouched.

Acetate here is a counter-ion — a small charged partner that balances the peptide’s own charge so it can be isolated as a dry solid. Peptides are routinely supplied this way. The practical consequence is that gross vial weight and peptide content are not the same number, which is one of the things a certificate of analysis exists to separate. How to read a peptide certificate of analysis sets out which figure on the document is which.

Which Has the Larger Research Record?

Neither, and the honest answer depends on which question is asked. Semax has the broader animal literature; Selank has the more specific proposed mechanism. Both records sit entirely in model systems — cell and enzyme assays, and work in rats — and neither of them is large.

Read that table as a description of what has been measured, not as a ranking. A rat transcription result stays a rat transcription result: it does not become a statement about anything happening in a person by being repeated confidently enough. Where a research field is named above — neurotransmission, immune response — it names the discipline the work belongs to, and nothing more.

What Does ARP Supply?

Australian Research Peptides lists Semax and Selank as separate freeze-dried vials under Neuropeptide Research, dispatched from Sydney. The table below is read from the catalogue as this page renders, rather than typed into the copy.

Availability is shown on each listing rather than here, because it changes without this page changing. The strengths differ only in how much powder was weighed into the vial.

No batch certificate is published for either compound at the moment. The certificate library lists every document ARP has published and shows the remaining strengths as coming soon.

Common Questions

Related Guides

• BPC-157 vs TB-500: what is the difference — the other pair mistaken for variants of one another.
• Peptide types, categories and blends — how the catalogue is grouped, and what a blend fixes.
• Peptide testing, purity and certificates of analysis — peptide content against gross weight, on the document.
• Lyophilised peptides: storage and handling — why a sealed vial is warmed before the seal is broken.
• Peptide glossary and FAQ — heptapeptide, analogue and counter-ion, defined once.

Australian Research Peptides lists Semax and Selank side by side under Neuropeptide Research, each a sealed freeze-dried vial sent from Sydney, and each listing shows its own current stock.

Read this article as plain text — Semax vs Selank: What Is the Difference?, in Markdown — the full text in Markdown, without the page around it, for assistants, screen readers and offline reading.