Nootropic Peptides: Semax and Selank in Neuroscience

EXOMA Scientific Team · Publicado el 5 de enero de 2026 · Actualizado el 24 de agosto de 2026

Review of studies on the effects of Semax and Selank in animal models, including mechanisms of action on neurotrophic factors.

Introduction: two peptides, one school

In the study of molecules with the potential to modulate the central nervous system, few examples are as cited in the preclinical literature as Semax y Selank. Both share the same scientific lineage —they emerged from work on neuropeptides developed in Russia during the final decades of the 20th century— and both illustrate a recurring idea in short-peptide neurochemistry: modifying a fragment of an endogenous signaling molecule to obtain a more stable entity, and studying how that new sequence interacts with brain signaling axes.

This article compares, with objective data, the chemical identity of each peptide, the signaling axes attributed to them in the research literature, and why they are jointly studied. All the material presented here is for scientific research reference purposes (RUO); it does not constitute guidance for use or a dose recommendation.

You can consult the complete data sheets in the Semax compendium and the Selank compendium, or review the cognitive category to place them within the research catalog.

Semax: a heptapeptide derived from ACTH(4–10)

Semax is a heptapeptide whose sequence is Met-Glu-His-Phe-Pro-Gly-Pro. Its design starts from a fragment of adrenocorticotropic hormone —specifically the portion ACTH(4–10), corresponding to the residues Met-Glu-His-Phe— to which the extension is added Pro-Gly-Pro (PGP) at the C-terminal end.

This structural detail is central. The ACTH(4–10) fragment by itself is a sequence known for its role in signaling associated with attention and memory processes in animal models, but short linear peptides tend to degrade rapidly through the action of peptidases. The addition of the tripeptide Pro-Gly-Pro modifies that behavior: the bonds involving proline residues are sterically more resistant to enzymatic cleavage, so the PGP extension acts as a "stopper" that hinders proteolytic degradation from the ends of the chain. It is a design principle that appears again and again in peptide chemistry: taking advantage of the conformational rigidity of proline to prolong the integrity of the molecule.

In the research literature, Semax is associated with the modulation of neurotrophic factors, in particular the brain-derived neurotrophic factor (BDNF) and the nerve growth factor (NGF), as well as interactions with the melanocortin system. These axes are of interest because neurotrophic factors participate in synaptic plasticity processes -the set of changes that allow neuronal connections to strengthen or reorganize- which constitute a biological substrate widely studied in the neuroscience of learning and memory.

The complete data sheet for this molecule is available at /producto/semax.

Selank: a synthetic analog of tuftsin

Selank is likewise a heptapeptide, with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its starting point differs from that of Semax: it derives from the tuftsin, an endogenous tetrapeptide (Thr-Lys-Pro-Arg) with a recognized role in immune signaling. As in the case of Semax, the base sequence is extended with the tripeptide Pro-Gly-Pro at the C-terminus, applying exactly the same stabilization logic against peptidases.

The signaling axes that the research literature associates with Selank are different from those of Semax: it is linked to neurotransmission GABAergic -GABA is the main inhibitory neurotransmitter of the central nervous system- and with the modulation of the serotonin, in addition to retaining some activity related to its immunological origin, a direct inheritance from tuftsin. This dual profile —one foot in neurochemistry and another in immune signaling— is one of the reasons why Selank is studied as a molecule of multiple mechanisms.

See the research profile at /producto/selank.

Objective chemical comparison

The following table summarizes the verified chemical identity of both peptides. These are objective structural data (CAS number, molecular formula, molar mass and sequence), not efficacy claims.

An interesting structural observation: the formula of Semax includes an atom of sulfur (S), absent in Selank. That sulfur comes from the residue of methionine (Met) in the first position of its sequence —methionine is one of the two sulfur-containing amino acids—. Selank, whose sequence lacks sulfurized residues, does not present it. It is an example of how amino-acid composition is directly reflected in the empirical formula of each peptide.

Both share an identical mass in the terminal tripeptide, but diverge completely in their N-terminal core, which explains why their total molar masses differ by just over 60 Da despite having the same number of residues (seven).

The Pro-Gly-Pro motif: the chemistry of stability

It is worth pausing on what Semax and Selank have in common from the standpoint of molecular design, because it is the key that unites them as a school of neuropeptides.

Short linear peptides are, by nature, substrates of exopeptidases, enzymes that trim amino acids from the ends of the chain. A fragment such as ACTH(4–10) or such as tuftsin, exposed to this enzymatic environment, has a limited structural integrity. The strategy adopted in both cases was to add the motif Pro-Gly-Pro at the carboxyl end.

La proline is a singular amino acid: its side chain closes onto the nitrogen of the peptide backbone forming a ring, which confers a conformational rigidity that no other proteinogenic amino acid possesses. Peptide bonds adjacent to proline residues are geometrically less accessible to many peptidases. By placing two prolines flanking a glycine at the terminal end, a region that is difficult to enzymatically "bite" is created, which in practice prolongs the structural integrity of the molecule relative to the base fragment without the extension.

This is a reusable design principle, and its identical presence in two molecules with such different origins—one derived from a pituitary hormone, the other from an immunological peptide—shows a coherent working philosophy behind both.

Why are they studied together?

Semax and Selank often appear paired in the research literature and in discussions about neuropeptides for several converging reasons:

• Shared origin. Both arose from the same Russian scientific tradition of developing peptide analogues of endogenous molecules, and both apply the same structural stabilization strategy with Pro-Gly-Pro.
• Complementary axes. Their studied mechanisms do not overlap but rather complement each other. Semax is oriented toward neurotrophic (BDNF/NGF) and melanocortin signaling; Selank toward GABAergic and serotonergic neurotransmission. In neuroscience terms, one is associated predominantly with plasticity axes and the other with inhibitory/monoaminergic modulation axes.
• Analogous experimental format. Being heptapeptides of comparable mass and physicochemical behavior, they lend themselves to equivalent laboratory handling protocols, which facilitates their parallel study.

This complementarity is precisely what makes them a reference pair within the cognitive category of the research catalog: they represent two distinct approaches —trophic and neurotransmitter— to the modulation of central nervous system function.

Handling in the laboratory

Like most research peptides, Semax and Selank are supplied in the form lyophilized (freeze-dried) to maximize their stability during storage. Lyophilization removes the water from the product by means of sublimation under vacuum, leaving a solid powder that preserves the integrity of the molecule much better than a liquid solution.

Before any experimental work, the lyophilized material must be reconstituted. Correct preparation of the solution is a critical step that should be planned carefully; we have developed a dedicated guide to the procedure in Reconstitution guide for lyophilized peptides, and calculation tools such as the reconstitution calculator, the vial calculator and the unit converter to support experimental planning.

To compare the chemical identity of these peptides against others in the catalog, the comparator allows comparing objective parameters side by side.

Semax vs. Selank: contrast summary

If we had to condense the distinction into a single idea: are structural cousins with different grandparents. They share the same stabilizing Pro-Gly-Pro "tail" and the same length of seven residues, but their N-terminal "head" comes from different molecular families —one hormonal (ACTH), the other immunological (tuftsin)— and that difference in origin translates into distinct signaling axes in the research literature.

For the researcher approaching these compounds for the first time, the useful reading is this: they are neither interchangeable nor redundant. Each is studied for its own interaction profile, and their value as a pair lies precisely in the fact that they address different aspects of the neurochemistry of the central nervous system.

Related reading

If you are interested in the design and characterization of research peptides beyond nootropics, these resources broaden the picture:

• BPC-157: mechanisms of action in preclinical models
• TB-500 (Thymosin Beta-4) and tissue regeneration
• How to calculate peptide dosing: a practical guide
• Full catalog at /productos and technical data sheets in the /compendio

Disclaimer (RUO). All products and information presented here are intended exclusively for scientific research (Research Use Only). The content of this article is educational and serves as a technical reference; it describes verified structural data and signaling axes reported in the research literature, and does not constitute clinical guidance, a recommendation for use, or a claim of efficacy. The chemical identity data (CAS, molecular formula, molar mass and sequence) are provided for laboratory characterization purposes.

References

Material for research use only. Verified primary sources supporting the scientific claims of this article:

1. Dolotov OV, Seredenina TS, Levitskaya NG, et al. The heptapeptide SEMAX stimulates BDNF expression in different areas of the rat brain in vivo. Dokl Biol Sci. 2003;391:292-295. doi:10.1023/a:1025177812262. PMID 14556513. (animal)
2. Dolotov OV, Karpenko EA, Inozemtseva LS, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006;1117(1):54-60. doi:10.1016/j.brainres.2006.07.108. PMID 16996037. (animal)
3. Filatova E, Kasian A, Kolomin T, et al. GABA, Selank, and olanzapine affect the expression of genes involved in GABAergic neurotransmission in IMR-32 cells. Front Pharmacol. 2017;8:89. doi:10.3389/fphar.2017.00089. PMID 28293190. (in vitro)
4. Kasian A, Kolomin T, Andreeva L, et al. Peptide Selank enhances the effect of diazepam in reducing anxiety in unpredictable chronic mild stress conditions in rats. Behav Neurol. 2017;2017:5091027. doi:10.1155/2017/5091027. PMID 28280289. (animal)
5. Zozulia AA, Neznamov GG, Siuniakov TS, et al. Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the therapy of generalized anxiety disorders and neurasthenia. Zh Nevrol Psikhiatr Im S S Korsakova. 2008;108(4):38-48. PMID 18454096. (human)

Products available at EXOMA

• Selank
• Semax
• Semax + Selank