Semax vs Selank: A Comparison of Two Russian Heptapeptide Nootropics

Semax and Selank look like the same molecule on a vendor sheet. Both are seven-residue synthetic peptides. Both end in the same C-terminal Pro–Gly–Pro tail. Both were designed at the same Russian institute in the 1990s. Both are typically delivered as a nasal spray in the clinical literature. Both are registered as drugs only in the Russian Federation. Both are heavily described in the Russian-language scientific record and only thinly translated into Western journals.

That surface similarity hides what is actually a careful pharmacological design: two peptides built with the same C-terminal stabilizer, but on top of two completely different parent biomolecules — one fragment of adrenocorticotropic hormone, one fragment of the immune-system tetrapeptide tuftsin — and therefore aimed at two completely different signaling axes in the brain. This article walks through each peptide on its own terms and then sets them alongside each other so the differences are unambiguous.

Nothing here is a recommendation. Semax is supplied by PepMax under the slug semax; Selank is supplied under the slug selank; both are for laboratory research use only. Neither has been approved by FDA, EMA, MHRA, or Health Canada for any human or veterinary therapeutic use.

At a glance

The most efficient way to read these two compounds is side by side. Sequence and structural details below are taken from the original Russian Academy of Sciences synthesis papers and independent confirmations^[1][2].

Origins — one institute, two peptides

Both compounds emerged from the same group: the laboratory of Igor Petrovich Ashmarin and Nikolai Fedorovich Myasoedov at what is now the Institute of Molecular Genetics of the Russian Academy of Sciences, in collaboration with the Department of Human and Animal Physiology at Lomonosov Moscow State University. The program ran from the late 1980s through the 2000s and produced a family of regulatory-peptide analogs designed around two principles: (1) start from a known endogenous neuropeptide or peptide hormone fragment; (2) graft a Pro–Gly–Pro tail to confer protease resistance.

Semax was the earlier of the two. It was characterized in a series of papers in the early-to-mid 1990s as a non-hormonal analog of ACTH(4–10) that retained the cognitive and neurotrophic effects of the parent fragment without producing the adrenal-axis stimulation of full ACTH^[1]. Selank followed in the mid-to-late 1990s as a separate program built on the immunomodulatory tetrapeptide tuftsin, with the explicit design goal of an anxiolytic peptide that did not act through the benzodiazepine binding site^[2].

Sequences and the PGP stabilizer

Reading the two sequences side by side makes the design pattern explicit:

Semax  →  Met–Glu–His–Phe | Pro–Gly–Pro
Selank  →  Thr–Lys–Pro–Arg | Pro–Gly–Pro

The first four residues encode the biological identity. In Semax, MEHF is the active N-terminal fragment of ACTH(4–10), retaining the histidine and phenylalanine that the cognitive-effect literature on ACTH had implicated. In Selank, TKPR is native tuftsin — the same four residues that occur in the Fc region of immunoglobulin G heavy chain and that have been described as immunostimulatory and behaviorally anxiolytic-adjacent in older tuftsin work.

The C-terminal Pro–Gly–Pro tail is the same in both. It is what made the molecules clinically usable: free MEHF or free TKPR are degraded in plasma within minutes; with the PGP tail, intranasal administration produces measurable CNS effects in animal and human studies. This is also why both molecules are typically administered intranasally rather than orally — even with PGP, oral bioavailability remains low, but olfactory- and trigeminal-route delivery bypasses systemic peptidases.

Semax — what it is

Semax is a non-hormonal, neurotropic analog of ACTH(4–10). It does not stimulate cortisol release the way intact ACTH does — the truncation removes the hormonal portion of the parent molecule. What remains is a peptide that, in the Russian-language literature, is described as activating CNS systems involved in attention, learning, and recovery from ischemic injury.

Reported mechanisms

The most directly characterized signaling event for Semax is upregulation of brain-derived neurotrophic factor (BDNF) and of its receptor TrkB in the hippocampus. Dolotov and colleagues (2006) reported that intranasal Semax in rats produced increased BDNF and TrkB mRNA and protein in hippocampal regions associated with learning and memory^[4]. Storozhevykh and colleagues (2007) reported that both Semax and its free PGP fragment attenuated calcium dysregulation and improved survival of cortical neurons under glutamate toxicity, consistent with a neuroprotective mode of action^[3].

Two additional pathways recur. Eremin and colleagues (2005) reported that Semax activated dopaminergic and serotonergic signaling in rat brain regions associated with attention and motivation^[11]. And Kost and colleagues (2001) reported that Semax inhibited the enkephalin-degrading enzymes in human serum, prolonging the action of endogenous opioid peptides — a mechanism that Semax shares with Selank^[12].

Reported effects in literature

The Russian behavioral literature on Semax describes effects on attention, learning under cognitive load, and recovery of neurological function after experimentally induced cerebral ischemia. Inozemtseva and colleagues (2008) used c-Fos expression as a marker of neuronal activation and reported that intranasal Semax produced selective activation in cortical and hippocampal regions consistent with the cognitive-effect profile in behavioral assays^[10].

It is worth being explicit about what the literature does notclaim. The Semax record is consistent with the description “activating” and “cognitively oriented”; it is not described as anxiolytic, sedative, or sleep-modifying. The functional axis is alertness and learning, not calm.

Clinical research

The largest body of clinical work on Semax addresses ischemic cerebrovascular disease. Gusev, Skvortsova, and colleagues (1997) reported a controlled study in patients with acute hemispheric ischemic stroke in which intranasal Semax was associated with accelerated improvement on neurological scales and with electrophysiological signatures of cortical recovery^[5]. This study and follow-up Russian work formed the basis for Semax’s registration in the Russian Federation as a treatment for acute ischemic stroke and transient ischemic attack.

Selank — what it is

Selank is a metabolically stabilized analog of tuftsin, the four-residue Thr–Lys–Pro–Arg peptide derived from the Fc region of the IgG heavy chain. Tuftsin itself was studied in the 1980s and 1990s as an immunostimulatory factor that also showed behavioral anti-anxiety effects in rodent models. The original Russian program asked whether appending the Pro–Gly–Pro stabilizer would yield a clinically usable anxiolytic peptide; the answer became Selank^[2].

Reported mechanisms

The most consistent mechanistic finding in the Selank literature is positive allosteric modulation of the GABAergic system. In contrast to benzodiazepines, which act as positive allosteric modulators at the benzodiazepine binding site of the GABA-A receptor, Selank is reported to influence GABA-A receptor function through a different, non-benzodiazepine binding interaction — producing the anxiolytic phenotype without the sedative, amnestic, or motor-impairing side effects characteristic of benzodiazepines^[7].

A second pathway is shared with Semax: inhibition of the enkephalin-degrading enzymes leucine aminopeptidase and angiotensin-converting enzyme, which prolongs the half-life of endogenous enkephalins. Kost and colleagues (2001) reported this enzyme-inhibitory activity for both Semax and Selank in human serum^[12]. Tallerova and colleagues, and other groups working with Selank, have also reported modulation of serotonergic signaling and cytokine balance, consistent with the immunomodulatory–anxiolytic axis that Selank’s tuftsin parentage suggests.

Reported effects in literature

Selank’s reported effects in behavioral models cluster around anxiolysis without sedation. Kozlovskii and Danchev (2003) reported that Selank optimized performance on a conditioned active-avoidance task in rats — the animals retained the learning, but with a lower stress signature and without the motor impairment characteristic of anxiolytic doses of benzodiazepines^[6]. Volkova and colleagues (2016) published a comparative analysis with classical benzodiazepines and reported that Selank’s anxiolytic potency was in a similar range to short-course benzodiazepine therapy without the sedation, dependence, or rebound profile^[7].

As with Semax, the literature is explicit about what Selank is not. It is not described as cognitively activating, nor as a treatment for attention or learning deficits. The reported axis is calm without sedation — not alertness.

Clinical research

Two Russian-language clinical reports anchor the Selank human evidence base. Zozulya and colleagues (2008) reported on Selank in generalized anxiety disorder and neurasthenia, describing a response profile in the same range as short-course benzodiazepine therapy, with the absence of the typical benzodiazepine adverse-event signature^[8]. Medvedev and colleagues (2015) followed up with a clinical-practice-style report on Selank as an adjunct to standard pharmacotherapy in anxiety disorders^[9]. Both reports underpin Selank’s registration in the Russian Federation for generalized anxiety disorder.

Side-by-side: where they diverge

The structural similarity of Semax and Selank invites the assumption that they are functionally similar. The literature does not support that assumption. Reading the two evidence bases together, the divergence is consistent across mechanism, behavioral effect, and clinical indication.

A useful mental model: the two peptides share a stabilizer (PGP) and a route (intranasal), but their parent biology is the divider. Semax inherits the cognitive-and-trophic signature of the ACTH(4–10) lineage. Selank inherits the immune-and-anxiolytic signature of the tuftsin lineage. The PGP tail is structural; the first four residues are the pharmacology.

Limitations of the evidence base

Both literatures share three structural limitations that any researcher should weigh before drawing conclusions from them.

First, language and venue concentration. The majority of human and clinical work on both Semax and Selank is published in Russian-language journals, principally Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova(the Korsakov Journal of Neurology and Psychiatry) and adjacent Russian Academy of Sciences outlets. Western Phase 3 trials registered on ClinicalTrials.gov or EudraCT do not exist for either compound as of this writing. A researcher who reads only English-language literature will see a small fraction of the actual evidence base — mostly mechanistic rodent studies translated into Western journals through Russian first-authors.

Second, single-program origin.Like the BPC-157 literature (which is concentrated in the Sikirić group at Zagreb), the Semax and Selank literatures are concentrated in the Ashmarin–Myasoedov line of laboratories. Independent replication outside of that institutional network is sparse. This is a known limitation of Russian Academy peptide research; it is also a property of the compounds’ development history, not an indictment of any individual paper.

Third, intranasal delivery interpretation. Both compounds are typically administered intranasally in human studies. The direct nose-to-brain delivery route complicates comparisons to systemic dosing in rodent models, and pharmacokinetic data on the actual brain concentration achieved by intranasal administration in humans is limited. Effect sizes in the clinical literature should not be back-translated to a specific brain exposure.

Reconstitution & handling

Both compounds are supplied as lyophilized powders for laboratory research use. They share the standard handling expectations of small synthetic peptides:

• Reconstitute with bacteriostatic water (0.9% benzyl alcohol) for stability over multiple days, or sterile water for shorter-duration single-use studies. Mix gently; do not vortex.
• Store the lyophilized vial sealed in a cool, dry, dark location prior to reconstitution. Once reconstituted, refrigerate (2–8 °C) and use within the protocol-defined window.
• Avoid repeated freeze–thaw cycles. Aliquot if multiple thaws are anticipated.
• Both peptides degrade more rapidly in solution than in the lyophilized state — the motivation for the same lyophilization strategy used across the PepMax catalog.

Further reading

For readers approaching either compound for the first time, the most useful entry points in the English-language literature are the mechanism papers cited above — in particular Dolotov et al. 2006 for Semax^[4], Kozlovskii & Danchev 2003 for Selank^[6], and Kost et al. 2001 for the shared enkephalin-degrading-enzyme inhibition pathway^[12]. Russian-language readers will find a substantially deeper clinical literature in Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova and in the Doklady Biological Sciences archive.

Companion PepMax research articles cover related subjects: What ≥99% purity actually means for the analytical-quality questions that apply to all peptides we ship; How we verify peptide purity for the HPLC and mass-spectrometry workflow used on every Semax and Selank lot; and BPC-157 compound profile for a comparable evidence-quality discussion of another peptide whose literature is dominated by a single research group.