# Semax vs Selank: What Is the Difference?

Semax and Selank are two different heptapeptides, and the difference is the first four amino acids. Both end in the same Pro-Gly-Pro tail. Semax is Met-Glu-His-Phe-Pro-Gly-Pro, built on a fragment of adrenocorticotropic hormone; Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, built on tuftsin. This guide sets out what each has been studied for, the two studies that placed them side by side, and what neither has. Supplied for in vitro research purposes only.

- Source: https://www.australianresearchpeptides.au/articles/semax-vs-selank
- Reading time: 9 minute read
- Published: 2026-09-02
- Publisher: Australian Research Peptides

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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.

_Semax and Selank compared by sequence, length, starting motif, shared ending, molecular formula, research themes, direct comparative evidence and main limitation_

|  | Semax | Selank |
| --- | --- | --- |
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Length | 7 amino acids | 7 amino acids |
| Starting motif | Met-Glu-His-Phe, positions 4 to 7 of adrenocorticotropic hormone | Thr-Lys-Pro-Arg, the sequence of tuftsin |
| Shared ending | Pro-Gly-Pro | Pro-Gly-Pro |
| Molecular formula | C37H51N9O10S, 813.9 g/mol | C33H57N11O9, 751.9 g/mol |
| Research themes | Gene transcription after induced stroke in rats; neurotrophin and immune-response genes | Neurotransmission gene expression in rat frontal cortex, and a proposed GABA-related link |
| Direct comparative evidence | Two studies place both in one experiment: an enzyme assay and a brain-imaging study | The same two studies. Neither measures a clinical outcome |
| Main limitation | Most published findings are animal transcription data, not behaviour or outcome | Same, and its mechanism is inferred from gene expression rather than measured directly |

## 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: what happens to gene activity in the brain after an induced stroke in rats. A 2010 study using a rat model of blocked blood flow reported that Semax raised the transcription of genes for several neurotrophins and their receptors in the cortex. Transcription is the step where a gene is read out into the message a cell uses to build a protein.

A 2017 genome-wide study in the same rat model reported that the biological process most markedly affected was the immune response, with changes across antigen-presentation and interferon signalling. Both findings are animal data, and both measure gene activity rather than behaviour. [The Semax listing](https://www.australianresearchpeptides.au/products/semax) 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 84 genes involved in neurotransmission in the frontal cortex of rats, one and three hours after Selank or GABA was given. Forty-five of those genes had changed at one hour and 22 at three hours, and at the one-hour point the changes produced by Selank correlated positively with those produced by GABA.

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](https://www.australianresearchpeptides.au/products/selank) 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 tested it directly. The 2010 rat stroke work gave Pro-Gly-Pro on its own as a third arm, and the tripeptide also raised transcription of several of the same genes. The profiles overlapped only partly: Semax acted selectively on the ischaemic cortex, while the tripeptide’s influence was described as mainly unspecific.

One name is on all five papers cited here.

N. F. Myasoedov is an author of every study referenced at the foot of this page, across nineteen years and both compounds. That does not make any of them wrong, and nothing above is disputed on that basis. It does mean five citations are not five independent confirmations, which is worth knowing before weighing any claim about either peptide.

## 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 is a clinical outcome trial, 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 dose-dependent way. This was done in glassware, not in a living subject. Semax halved the enzymes’ activity at a concentration of about 10 micromolar and Selank at about 20, making Semax the more potent of the pair in that assay. Their five-amino-acid fragments were active too; the three-, four- and six-amino-acid fragments were not.

**The imaging study, 2020.** Fifty-two healthy participants were scanned three times — before an injection, and five and twenty minutes after it — receiving Semax, Selank or placebo. The scan was resting-state functional MRI, meaning the participant lies still and performs no task while connectivity between brain regions is measured. The authors reported differences involving the right amygdala and a region of the right temporal cortex, and described both shared and separate effects for the two peptides.

That is the entire direct comparison. A search of ClinicalTrials.gov on 2 September 2026, scoped to the intervention field, returned no registered study of either peptide. Semax returned nothing at all. Selank returned two apparent hits, and both are unrelated brain-stimulation trials rather than studies of the compound.

## 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 Nootropic Peptides, 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](https://www.australianresearchpeptides.au/articles/peptide-testing-purity-coa) sets out which figure on the document is which.

## Which Has the Stronger Evidence?

Neither, and the honest answer depends on which question is asked. Semax has the broader animal literature; Selank has the more specific proposed mechanism. On the evidence type that would matter most — a registered clinical trial — both have nothing.

_Types of published evidence available for Semax and Selank, from registered clinical trials down to in-vitro enzyme work_

| Type of evidence | Semax | Selank |
| --- | --- | --- |
| Registered clinical trial | None found on ClinicalTrials.gov, 2 September 2026 | None found on ClinicalTrials.gov, 2 September 2026 |
| Measurement in people | One brain-connectivity scan study, 52 healthy participants | That same study, same participants |
| Animal gene-expression work | Two rat studies cited here: neurotrophin genes, then genome-wide immune-response genes | One rat study cited here: 84 neurotransmission genes in frontal cortex |
| Animal behaviour or outcome | Not covered by the studies cited here | Not covered by the studies cited here |
| In-vitro enzyme work | Inhibited human serum enkephalin-degrading enzymes, the more potent of the two | Inhibited the same enzymes at roughly twice the concentration |
| Independence of the sources | Shares an author with every other study cited here | Shares an author with every other study cited here |

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 attention, memory or mood 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 Nootropic Peptides, dispatched from Sydney. The table below is read from the catalogue as this page renders, rather than typed into the copy.

_Semax and Selank vial strengths, stock codes and prices, read from the ARP catalogue_

| Listing | Strength | Stock code | Price |
| --- | --- | --- | --- |
| [Semax](https://www.australianresearchpeptides.au/products/semax) | [10 mg](https://www.australianresearchpeptides.au/products/semax/10mg) | ARP-SEMAX-10 | $65.99 |
| [Semax](https://www.australianresearchpeptides.au/products/semax) | [30 mg](https://www.australianresearchpeptides.au/products/semax/30mg) | ARP-SEMAX-30 | $139.99 |
| [Selank](https://www.australianresearchpeptides.au/products/selank) | 30 mg | ARP-SELANK-30 | $149.99 |

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](https://www.australianresearchpeptides.au/coa) lists every document ARP has published and shows the remaining strengths as coming soon.

## Common Questions

### Is Semax or Selank Better?

Neither is a better version of the other, because they have never been measured against each other on anything that would settle it. The two studies placing them side by side compared an enzyme inhibition in glassware and a brain-connectivity scan, not an outcome. Which suits a piece of research depends on what that research is measuring.

### Are Semax and Selank Both Heptapeptides?

Yes. Semax and Selank are both heptapeptides, meaning chains of seven amino acids, and both close with the same Pro-Gly-Pro tail. The first four positions differ completely, which is why their formulas and masses differ: Semax is C37H51N9O10S at 813.9 g/mol, Selank is C33H57N11O9 at 751.9 g/mol.

### What Does the Pro-Gly-Pro Ending Do?

Pro-Gly-Pro is the three-amino-acid tail both peptides end in, and it is not inert. In a 2010 rat study it was given on its own, and it raised transcription of several of the same genes Semax raised. The two profiles were not identical: the tripeptide’s influence was described as mainly unspecific, while Semax’s was selective for the ischaemic cortex. That is the one published test of the shared tail found for this page.

### Can I Buy Semax and Selank in Australia?

Australian Research Peptides supplies both from within Australia, as separate listings under Nootropic Peptides, so an order does not cross a border or clear customs. Each product page shows its own current stock: [Semax](https://www.australianresearchpeptides.au/products/semax) and [Selank](https://www.australianresearchpeptides.au/products/selank).

## Related Guides

- [BPC-157 vs TB-500: what is the difference](https://www.australianresearchpeptides.au/articles/bpc-157-vs-tb-500) — the other pair mistaken for variants of one another.
- [Peptide types, categories and blends](https://www.australianresearchpeptides.au/articles/peptide-types-categories-blends) — how the catalogue is grouped, and what a blend fixes.
- [Peptide testing, purity and certificates of analysis](https://www.australianresearchpeptides.au/articles/peptide-testing-purity-coa) — peptide content against gross weight, on the document.
- [Lyophilised peptides: storage and handling](https://www.australianresearchpeptides.au/articles/lyophilised-peptides-storage-handling) — why a sealed vial is warmed before the seal is broken.
- [Peptide glossary and FAQ](https://www.australianresearchpeptides.au/articles/peptide-glossary-faq) — heptapeptide, analogue and counter-ion, defined once.

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

## References

1. [PubChem Compound CID 9811102 (Semax, Met-Glu-His-Phe-Pro-Gly-Pro), molecular formula C37H51N9O10S](https://pubchem.ncbi.nlm.nih.gov/compound/9811102)
2. [PubChem Compound CID 11765600 (Selank, Thr-Lys-Pro-Arg-Pro-Gly-Pro; also indexed as TP-7), molecular formula C33H57N11O9](https://pubchem.ncbi.nlm.nih.gov/compound/11765600)
3. [PubChem Compound CID 156080 (Tuftsin, Thr-Lys-Pro-Arg)](https://pubchem.ncbi.nlm.nih.gov/compound/156080)
4. [PubChem Compound CID 155489759 (Selank acetate), molecular formula C35H61N11O11; the acetate salt carries its own record, separate from Selank at CID 11765600](https://pubchem.ncbi.nlm.nih.gov/compound/155489759)
5. [PubChem Compound CID 172638603 (N-acetyl semax amidate), molecular formula C39H54N10O10S](https://pubchem.ncbi.nlm.nih.gov/compound/172638603)
6. [Dmitrieva VG, Povarova OV, Skvortsova VI, et al. "Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia." Cellular and Molecular Neurobiology 2010;30(1):71-79 (PMID 19633950)](https://pubmed.ncbi.nlm.nih.gov/19633950/)
7. [Medvedeva EV, Dmitrieva VG, Limborska SA, Myasoedov NF, Dergunova LV. "Semax, an analog of ACTH(4-7), regulates expression of immune response genes during ischemic brain injury in rats." Molecular Genetics and Genomics 2017;292(3):635-653 (PMID 28255762)](https://pubmed.ncbi.nlm.nih.gov/28255762/)
8. [Volkova A, Shadrina M, Kolomin T, et al. "Selank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission." Frontiers in Pharmacology 2016;7:31 (PMID 26924987)](https://pubmed.ncbi.nlm.nih.gov/26924987/)
9. [Kost NV, Sokolov OYu, Gabaeva MV, et al. "Semax and selank inhibit the enkephalin-degrading enzymes from human serum." Bioorganicheskaia Khimiia 2001;27(3):180-183 (PMID 11443939); article in Russian with an English abstract](https://pubmed.ncbi.nlm.nih.gov/11443939/)
10. [Panikratova YR, Lebedeva IS, Sokolov OY, et al. "Functional Connectomic Approach to Studying Selank and Semax Effects." Doklady Biological Sciences 2020;490(1):9-11 (PMID 32342318)](https://pubmed.ncbi.nlm.nih.gov/32342318/)
11. [ClinicalTrials.gov, registered-study search on the intervention field for Semax and for Selank (checked 2 September 2026)](https://clinicaltrials.gov/search?intr=Semax)

## Related compounds

- [Semax](https://www.australianresearchpeptides.au/products/semax)
- [Selank](https://www.australianresearchpeptides.au/products/selank)

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_All products supplied by Australian Research Peptides are for in vitro research purposes only._