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Semax vs Selank: What the Research Does and Doesn't Compare

By The Bionova Club Team

Disclosure: Bionova Club sells Semax and Selank, linked below.

Research use only. All Bionova products are sold strictly for in-vitro and laboratory research by qualified professionals. They are not drugs, food, or cosmetics, are not approved by the FDA, and are not for human or veterinary use. Nothing in this article is medical advice or a claim about effects in people.

Semax and Selank are almost always mentioned in the same breath. Both are short synthetic peptides, both have been studied mainly in Moscow laboratories (every paper cited below lists a Moscow affiliation), and both end in the same three amino acids. So it is natural to ask which one is "better." The honest answer is that the published literature rarely puts them side by side, and when it does, the comparisons are narrow.

This overview explains what each peptide is, what the research on each has focused on, the handful of studies that actually examined both, and the gaps a careful researcher should keep in mind. If you are sourcing material, see our Semax 5 mg and Selank 5 mg research peptides.

Semax vs Selank at a glance

  • Length
    • Semax: 7 amino acids (heptapeptide)
    • Selank: 7 amino acids (heptapeptide)
  • Sequence
    • Semax: Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP)
    • Selank: Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP)
  • Modeled on
    • Semax: an analog of ACTH(4-10), built on the ACTH(4-7) sequence (Met-Glu-His-Phe) plus Pro-Gly-Pro (Dolotov et al., 2006)
    • Selank: Tuftsin (TKPR), a tetrapeptide derived from immunoglobulin G
  • Shared feature
    • Semax: C-terminal Pro-Gly-Pro (PGP)
    • Selank: C-terminal Pro-Gly-Pro (PGP)
  • Molecular formula
    • Semax: C37H51N9O10S
    • Selank: C33H57N11O9
  • Molecular weight
    • Semax: ~813.9 g/mol
    • Selank: ~751.9 g/mol
  • Main research themes
    • Semax: Neurotrophin (BDNF/trkB) expression; gene expression in rodent ischemia models
    • Selank: GABAergic gene expression and GABA-binding assays; immune-related gene expression
  • Oxidation-sensitive residues
    • Semax: Yes, methionine (M)
    • Selank: None of C, M or W

Sequence and formula data: PubChem, Semax and PubChem, Selank; sequences also given in Kost et al., 2001. The same sequences and formulas appear on Bionova's Semax 5 mg and Selank 5 mg product pages.

What is Semax?

Semax is a synthetic analog of a short piece of adrenocorticotropic hormone (ACTH), described as an analog of ACTH(4-10) (Dolotov et al., 2006). Structurally it is the ACTH(4-7) sequence, Met-Glu-His-Phe, with a Pro-Gly-Pro tail added, which is why it is also written ACTH(4-7)PGP (Filippenkov et al., 2020). That design choice comes up again and again in the literature, so it is worth understanding.

Why the Pro-Gly-Pro tail matters

Short peptides tend to be broken down quickly by peptidases. Proline-rich "glyproline" sequences such as Pro-Gly-Pro were studied by Ashmarin and colleagues at Moscow State University as a way to make regulatory peptides more resistant to enzymatic breakdown (Ashmarin et al., 2005). Follow-up work measured how Semax holds up against proteolysis in different biological media (Shevchenko et al., 2013).

What Semax research has examined

Most Semax papers come from rodent and cell models. Two themes dominate:

  • Neurotrophin expression. Studies in rats measured brain-derived neurotrophic factor (BDNF) and trkB after Semax exposure, reporting changes in expression in the hippocampus (Dolotov et al., 2006).
  • Gene expression in ischemia models. Genome-wide transcription studies in rat models of focal brain ischemia examined how Semax shifted the expression of immune- and vascular-related genes (Medvedeva et al., 2014), with later transcriptome-level follow-up work (Filippenkov et al., 2020).

These are mechanism-oriented findings in animal and cell systems. They describe what was measured in those models and should not be read as evidence of any effect in people.

What is Selank?

Selank is a synthetic analog of tuftsin, a natural four-residue peptide (Thr-Lys-Pro-Arg) cleaved from immunoglobulin G. As with Semax, the developers extended the core sequence with Pro-Gly-Pro, giving the heptapeptide TKPRPGP.

What Selank research has examined

Selank's literature leans toward two areas:

  • GABAergic signaling. Gene-expression studies in rodents and in IMR-32 neuroblastoma cells examined Selank's influence on genes involved in GABAergic neurotransmission (Volkova et al., 2016; Filatova et al., 2017). Radioligand-binding work explored whether Selank acts as an allosteric modulator of GABA binding in brain membrane preparations (Vyunova et al., 2018).
  • Immune-related gene expression. Because tuftsin is an immunomodulatory peptide, several studies tracked inflammation-related gene expression in mouse tissue after Selank exposure (Kolomin et al., 2011).

Again, these are preclinical and in-vitro measurements, and the same caution applies.

Where the research actually compares Semax and Selank

Searching PubMed for both names together returns only a few studies that examine the two peptides in the same experiment. Two preclinical examples stand out:

  • Kost et al., 2001
    • Model: Human serum enzymes, in vitro
    • What was compared: Inhibition of enkephalin-degrading enzymes. Both peptides inhibited them; reported IC50 values were about 10 µM for Semax and 20 µM for Selank.
  • Slominsky et al., 2017
    • Model: Rat 6-OHDA lesion model
    • What was compared: Behavior in maze tests. Neither peptide changed motor activity; the authors reported a behavioral difference in the elevated maze for Selank but not Semax.

The enzyme study is the cleanest head-to-head comparison, because both peptides were tested in the same assay. It also points to a plausible shared mechanism: both contain the PGP motif, and the authors found that only the pentapeptide fragments kept the inhibitory activity; the tri-, tetra- and hexapeptide fragments did not. The rat study is useful mainly as a reminder that, even in one model, the two peptides were not interchangeable on every measure.

What the research doesn't compare

If you are designing an experiment or simply reading competitor claims, these gaps matter:

  1. No large head-to-head studies. There is no well-powered study that directly ranks Semax against Selank on any outcome.
  2. Concentrated authorship. All eleven papers cited here list Moscow institutions as author affiliations, and nine list the Institute of Molecular Genetics of the Russian Academy of Sciences.
  3. Language barrier. A meaningful share of the literature is published in Russian, with only an English abstract indexed in PubMed.
  4. Different models, different endpoints. Semax work clusters around neurotrophins and ischemia models; Selank work clusters around GABAergic and immune gene expression. Comparing results across those models is not a true comparison.
  5. Regulatory status. Neither peptide is approved by the FDA. In the United States, both are sold as research chemicals only.

The practical takeaway: "Semax vs Selank" is better framed as "two related peptides with different research histories" than as a contest with a winner.

Storage notes for the lab

Both peptides are typically supplied as lyophilized powder. General storage rules for sealed lyophilized peptides apply: keep the sealed container cold, dry and away from light, avoid repeated temperature cycling, let it reach room temperature before opening, and store as directed on the product label.

One sequence-specific point: Semax contains methionine, which is prone to oxidation. Keeping the powder sealed and limiting air exposure is especially sensible for Semax. Selank contains none of the most oxidation-prone residues (cysteine, methionine, tryptophan), although like any peptide it is most stable kept dry and sealed.

New to the chemistry? Our primer What are peptides? explains sequences, amino acid codes and why lyophilization matters.

Key takeaways

  • Semax (MEHFPGP) is built on an ACTH fragment; Selank (TKPRPGP) is built on tuftsin. Both share a C-terminal Pro-Gly-Pro motif.
  • Semax research focuses on neurotrophin and gene-expression changes in rodent models; Selank research focuses on GABAergic and immune-related gene expression.
  • Only a few studies test both together, such as an in-vitro enzyme assay and a rat behavior study.
  • There is no large head-to-head study, and most work comes from one research network.
  • Both are research-only materials. Browse them alongside other single compounds in our research peptides category.

Frequently asked questions

What is the difference between Semax and Selank?

Both are synthetic seven-amino-acid peptides with the same Pro-Gly-Pro ending. Semax is modeled on a fragment of ACTH, while Selank is modeled on tuftsin, a peptide derived from immunoglobulin G. Their research literatures focus on different mechanisms.

Are Semax and Selank the same peptide?

No. They share only the last three residues. Semax is Met-Glu-His-Phe-Pro-Gly-Pro and Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, so their molecular formulas and weights differ.

Has any study compared Semax and Selank directly?

A few. A 2001 in-vitro study compared their inhibition of enkephalin-degrading enzymes, and a 2017 rat study compared behavior in a lesion model. None was a large comparative study.

Why do Semax and Selank both end in Pro-Gly-Pro?

The developers added the Pro-Gly-Pro glyproline motif to short regulatory peptides to make them more resistant to breakdown by peptidases. It is a design feature shared by both compounds.

Who developed Semax and Selank?

Every paper cited in this article lists a Moscow institution as an author affiliation, and nine of the eleven list the Institute of Molecular Genetics of the Russian Academy of Sciences (for example, Dolotov et al., 2006). We did not find a primary source documenting where each peptide was first developed.

How should Semax and Selank be stored in the lab?

As lyophilized powders, keep sealed vials cold, dry and protected from light, and let them reach room temperature before opening. Semax contains methionine, so limiting air exposure is especially useful. Store as directed on the product label.

Shop for your research: Semax and Selank, for laboratory research. Use code CLUB10 at checkout for 10% off.

References

  1. Kost NV, et al. Semax and selank inhibit the enkephalin-degrading enzymes from human serum. Bioorg Khim. 2001 (in Russian; English abstract). https://pubmed.ncbi.nlm.nih.gov/11443939/
  2. Slominsky PA, et al. Peptides semax and selank affect the behavior of rats with 6-OHDA induced PD-like parkinsonism. Dokl Biol Sci. 2017. https://pubmed.ncbi.nlm.nih.gov/28702721/
  3. Ashmarin IP, et al. Natural and hybrid ("chimeric") stable regulatory glyproline peptides. Pathophysiology. 2005. https://pubmed.ncbi.nlm.nih.gov/15837162/
  4. Shevchenko KV, et al. Stability of Semax acetyl to proteolysis in various biological media. Dokl Biol Sci. 2013. https://pubmed.ncbi.nlm.nih.gov/23652441/
  5. Dolotov OV, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006. https://pubmed.ncbi.nlm.nih.gov/16996037/
  6. Medvedeva EV, et al. The peptide semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia: genome-wide transcriptional analysis. BMC Genomics. 2014. https://pubmed.ncbi.nlm.nih.gov/24661604/
  7. Filippenkov IB, et al. Novel Insights into the Protective Properties of ACTH(4-7)PGP (Semax) Peptide at the Transcriptome Level Following Cerebral Ischaemia-Reperfusion in Rats. Genes (Basel). 2020. https://pubmed.ncbi.nlm.nih.gov/32580520/
  8. Volkova A, et al. Selank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission. Front Pharmacol. 2016. https://pubmed.ncbi.nlm.nih.gov/26924987/
  9. Filatova E, et al. GABA, Selank, and Olanzapine Affect the Expression of Genes Involved in GABAergic Neurotransmission in IMR-32 Cells. Front Pharmacol. 2017. https://pubmed.ncbi.nlm.nih.gov/28293190/
  10. Vyunova TV, et al. Peptide-based Anxiolytics: The Molecular Aspects of Heptapeptide Selank Biological Activity. Protein Pept Lett. 2018. https://pubmed.ncbi.nlm.nih.gov/30255741/
  11. Kolomin T, et al. Expression of inflammation-related genes in mouse spleen under tuftsin analog Selank. Regul Pept. 2011. https://pubmed.ncbi.nlm.nih.gov/21609736/
  12. PubChem (NIH/NLM). Semax, CID 9811102. https://pubchem.ncbi.nlm.nih.gov/compound/Semax
  13. PubChem (NIH/NLM). Selank, CID 11765600. https://pubchem.ncbi.nlm.nih.gov/compound/Selank

For laboratory research use only. Not for human consumption.