Selank vs Semax: Russian Heptapeptide Family Mechanism Comparison

Two peptides. Same institute, same decade, same delivery route. Selank and Semax were both developed at the Institute of Molecular Genetics in Moscow, both shortened from naturally occurring sequences (tuftsin and ACTH respectively), and both studied almost exclusively in Russian-language journals.

Researchers reach for them as a pair because they look like a matched experiment: one peptide targeted at anxiety endpoints, one at cognitive endpoints, in the same model systems by overlapping investigator groups. The comparison only holds up when the methods are read carefully.

Research content. The article below summarizes published preclinical and clinical literature. The compounds discussed are sold by Peerless Peptides for laboratory research use only and are not approved by the FDA for human or veterinary administration.

Last reviewed: May 18, 2026 by Peerless Research.

Summary

Selank and Semax are short synthetic peptides developed at the same Moscow institute in the 1990s and studied as a pair ever since. Selank derives from tuftsin (an immune-active tetrapeptide) and has been investigated for anxiolytic activity in rodent and small-n human studies. Semax derives from ACTH residues 4-10 and has been investigated for nootropic and neuroprotective effects in rodent and post-ischemic-stroke clinical studies.

Both are registered as prescription drugs in Russia; neither is FDA-approved. The published literature spans roughly four hundred papers, the majority in Russian, with methodological limitations that vary by study and matter for interpretation.

Note: The research described below was conducted in in vitro, animal-model, and small-n Russian clinical-trial systems. Human safety and efficacy of these compounds have not been established to FDA Phase 3 standards. This article is a literature review, not a recommendation of use.

The Two Molecules at a Glance

Both Selank and Semax are heptapeptides (seven-amino-acid sequences) built on a common design template. Each consists of a short biological "parent" sequence with an attached Pro-Gly-Pro (PGP) tail. The PGP extension is a stabilizer motif that the Institute of Molecular Genetics group used across multiple analogs. It blocks the proteases that would otherwise cleave the parent peptide in plasma and extracellular fluid, extending the active half-life from minutes to hours.

Property	Selank	Semax
Sequence (one-letter)	TKPRPGP	MEHFPGP
Sequence (parent + PGP)	tuftsin (TKPR) + PGP	ACTH(4-7) (MEHF) + PGP
Parent peptide	tuftsin (Thr-Lys-Pro-Arg, from the IgG heavy-chain CH2 domain)	ACTH residues 4-10 (Met-Glu-His-Phe-Pro-Gly-Pro)
Molecular formula	C₃₃H₅₇N₁₁O₉	C₃₉H₅₄N₁₀O₁₀S
Molecular weight (g/mol)	~751.9	~813.9
Standard Russian formulation	0.15% intranasal solution	0.1% or 1% intranasal solution
Russian regulatory registration	2009 (Peptogen)	1994 / 1996

The structural homology (both heptapeptides, both built on the PGP stabilizer template, both intranasal in standard Russian formulations) is what makes the side-by-side legible. The mechanistic divergence comes from the parents.

Institutional Provenance: IMG Moscow, Not Khavinson

The single most common error in English-language summaries of Selank and Semax is grouping them with "Khavinson bioregulators" or describing them as products of the "Russian peptide-bioregulator program." Both descriptions are wrong.

Selank and Semax were designed at the Institute of Molecular Genetics (IMG) of the Russian Academy of Sciences, in Moscow. The lab heads were Nikolai Myasoedov and Igor Ashmarin, with collaborators including Andreeva, Levitskaya, and (for Selank's clinical-development arc) Seredenin and Zozulya. The IMG group operated on a conventional medicinal-chemistry approach: take a short biological peptide with documented activity, attach a Pro-Gly-Pro stabilizer, exploit the proteolytic stability that the attachment buys.

The Khavinson program is something different. Vladimir Khavinson's St. Petersburg Institute of Bioregulation and Gerontology developed Epitalon, Pinealon, Cortagen, Vesugen, Cardiogen, Pancragen, and the broader "short-peptide bioregulator" catalog under a different research framework altogether. Khavinson's hypothesis is that two-to-four-amino-acid peptides bind in a sequence-specific manner to gene promoters and histone proteins, driving tissue-specific gene-expression changes. Whether that framework survives mainstream structural-biology review is a separate question and a different article.

What matters here is that the Khavinson catalog and the IMG Moscow catalog have no molecules in common. Different city, different decade, different research program, different mechanism story.

Grouping Selank and Semax under "Khavinson bioregulators" without qualification inherits the methodological liabilities of the Khavinson framework while obscuring the comparatively conventional pharmacology of the IMG Moscow analogs. The disambiguation is not a stylistic preference. It is a precondition for reading either literature honestly.

Selank's Mechanism: Tuftsin Lineage and GABAergic / Enkephalinergic Findings

Selank's parent, tuftsin, is a tetrapeptide (Thr-Lys-Pro-Arg) cleaved from the CH2 domain of the IgG heavy chain by spleen tuftsin endocarboxypeptidase and leukokininase. Tuftsin's endogenous activity is immune-modulatory: phagocyte activation, monocyte/macrophage stimulation, NK-cell modulation. The Selank analog adds the PGP tail and is studied principally for central-nervous-system endpoints rather than for tuftsin's classical immunological readouts.

The mechanism literature around Selank's CNS activity is built on four loosely related axes:

1. Enkephalinase inhibition. Selank slows degradation of endogenous enkephalins, which are opioid neuropeptides with anxiolytic and analgesic activity in rodent models. Reported in rat brain-tissue assays^[1].
2. GABAergic gene-expression modulation. A rat-cortex transcriptional study reported that intranasal Selank altered expression of multiple GABA-A receptor subunits and related interneuron markers^[2].
3. BDNF induction in rat hippocampus. Like Semax, Selank has been reported to increase brain-derived neurotrophic factor expression after intranasal administration in intact rats^[3].
4. Strain-dependent monoaminergic effects. Different rat and mouse strains produce different serotonin and norepinephrine turnover profiles after Selank, complicating cross-study interpretation.

A multi-axis mechanism story is worth flagging. When four separate molecular pathways are invoked to explain a single peptide's activity, it usually means no single, falsifiable target has been demonstrated, and that activity is being attributed to whichever downstream readout was easiest to measure in a given paper. Selank's mechanism literature has not yet produced the equivalent of, for example, Semax's clean BDNF/TrkB induction signal (below).

Semax's Mechanism: ACTH(4-10) Lineage and BDNF Induction

Semax's parent fragment is ACTH residues 4-10 (Met-Glu-His-Phe-Pro-Gly-Pro), the "behavioral pharmacophore" of corticotropin. The Dutch behavioral pharmacologist David de Wied established in the 1960s and 1970s that ACTH(4-10) carries the behavioral and cognitive activity of the full ACTH hormone without the adrenal-cortex-stimulating activity of the full hormone. The fragment retains CNS effects but does not provoke a corticosteroid response. Semax is essentially the de Wied fragment with the IMG Moscow PGP stabilizer attached.

The mechanistic anchor for Semax is Dolotov et al. 2006, published in Brain Research. A single intranasal 50 µg/kg dose of Semax produced a 1.4× increase in hippocampal BDNF protein, a 3× increase in BDNF exon-III mRNA, and a 2× increase in TrkB mRNA in intact rats^[4]. The finding was replicated by independent groups, including Klaus Engele's team at Saarland University in Germany. That replication is the strongest non-Russian mechanistic corroboration in either Selank's or Semax's literature.

A separate line of work shows that Semax administration shifts monoaminergic turnover (serotonin and dopamine) in rodent brain^[5]. The monoaminergic data are noisier than the BDNF data, and the interpretation is less mechanistically clean.

The 2020 Panikratova et al. functional MRI study added a connectomic dimension. Intranasal Semax in healthy human subjects altered resting-state functional connectivity between the amygdala, prefrontal cortex, and hippocampus in a pattern that differed from Selank's connectivity profile in comparable studies^[6]. The fMRI finding is interesting because it provides a non-invasive readout of differentiated central-nervous-system effects in humans. The sample size is small and replication is pending.

Clinical Evidence: What the Russian Trials Established (and What They Did Not)

The most-cited Selank clinical study is Zozulya, Seredenin et al. 2008, published in the Korsakov Journal of Neurology and Psychiatry^[7]. Sixty-two participants with generalized anxiety disorder or neurasthenia received fourteen days of intranasal Selank, with medazepam (a Hungarian-developed benzodiazepine common in Russian clinical practice) as the active comparator. The trial was open-label, single-site, and not pre-registered. There was no placebo arm.

Semax's clinical record is anchored by the Skvortsova group at the Pirogov Russian National Research Medical University. Veronika Skvortsova was Russian Minister of Health from 2012 to 2020, and her research team published the most-cited Semax clinical work: a 1997 acute-ischemic-stroke trial that compared thirty Semax-treated participants to eighty historical controls. The Skvortsova trial pre-dated modern preregistration and blinding norms. The historical-control design would not satisfy modern Western Phase 3 methodology.

Both clinical literatures share structural limitations: small n, single site, single investigator group, rarely blinded, no placebo, conducted before the modern preregistration era, published in Russian-language journals not always indexed in PubMed in full. These limitations do not mean the findings are wrong. They do constrain how strongly the findings can be generalized.

What the Comparison Literature Cannot Yet Settle

Several specific questions remain open in the published Selank-vs-Semax literature:

• Whether the intranasal route in Russian studies translates to other administration routes. The reported intranasal half-life of Selank in rat plasma is two to three minutes. The persistent CNS activity attributed to Selank is generally attributed to the PGP-tail metabolite, not to the intact parent. Which administration route best preserves the active species is not settled by the published data.
• Whether the rodent BDNF induction signal translates to humans. Dolotov's rodent finding for Semax is mechanistically clean. The human data are limited to the Panikratova fMRI study and the older Skvortsova stroke trials. The biomarker-to-clinical-outcome translation is not established.
• Whether Selank and Semax act on overlapping targets. Both have been reported to alter BDNF expression and to modulate monoaminergic turnover. Whether the overlapping findings reflect a shared downstream pathway or a common artifact of intranasal administration is unresolved.
• Whether combined administration produces additive, synergistic, or interfering effects. The published literature does not establish combined safety or efficacy. Comparison content does not extend to combination recommendations.

The brand of evidence-building visible in the published literature is closer to "exploratory pharmacology" than to confirmatory Phase 3 work. Findings should be weighted accordingly.

Regulatory Status: Russian Minzdrav and US FDA

Both peptides are registered as prescription drugs in Russia.

Selank was registered in 2009 by JSC Peptogen, with an indication for generalized anxiety disorder and a secondary indication in asthenia (a Russian clinical category broader than the Western fatigue diagnosis).

Semax was registered earlier: in 1994 for cognitive disorders and optic-nerve atrophy at 0.1% intranasal concentration, and in 1996 and 1998 for acute ischemic stroke at 1% intranasal concentration (Russian drug-register code P N000812/01). Semax is on the Russian Ministry of Health's list of vital and essential drugs (VED) per the December 7, 2011 government order.

Russian Minzdrav registration is not equivalent to FDA approval. The Russian regulator has different evidence requirements than the FDA, EMA, MHRA, Health Canada, TGA, or PMDA. Neither Selank nor Semax is FDA-approved for any indication.

In the US compounding-pharmacy regulatory channel, the two peptides have followed different paths:

• Semax is on the docket for the July 23-24, 2026 Pharmacy Compounding Advisory Committee meeting. The FDA proposes the compounds "Semax (free base)" and "Semax acetate" for review against the 503A Category 2 standards, with proposed indications limited to cerebral ischemia, migraine, and trigeminal neuralgia (Federal Register doc 2026-07361, written-comment docket FDA-2025-N-6895).
• Selank was removed from the FDA 503A Category 2 list on September 20, 2024 in the Evexias / Farmakeio settlement cohort but has never been PCAC-voted. Selank is not on the July 23-24, 2026 PCAC docket and was not in the April 2026 reclassification batch. This is an unusual posture: removed without a vote.

For US researchers, both compounds are sold as research-use-only chemicals through Peerless Peptides and other research chemical suppliers. Neither is FDA-approved for human or veterinary administration.

For PDP-level chemistry, regulatory updates, and supplier documentation, see the Selank entry and the Semax entry.

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References

1. Bondarenko EA, Belyaeva NV, Mokrushin AA, et al. (2001). Selank: a tuftsin analog with anxiolytic activity. Bull Exp Biol Med. PMID: 11550013.
2. Volkova A, Shadrina M, Kolomin T, et al. (2016). Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Front Pharmacol. 7:31. PMID: 26924987.
3. Inozemtseva LS, Karpenko EA, Dolotov OV, et al. (2008). Intranasal administration of the peptide Selank regulates BDNF expression in the rat hippocampus in vivo. Dokl Biol Sci. PMID: 18841804.
4. Dolotov OV, Karpenko EA, Inozemtseva LS, et al. (2006). Semax, an analog of ACTH(4-10), regulates BDNF expression in rat basal forebrain and hippocampus in vivo. Brain Res. 1117(1):54-60. PMID: 16996037.
5. Eremin KO, Kudrin VS, Saransaari P, et al. (2005). Semax, an ACTH(4-10) analogue with nootropic properties, activates dopaminergic and serotonergic brain systems in rodents. Neurochem Res. PMID: 15990752.
6. Panikratova YR, Vlasova RM, Akhutina TV, et al. (2020). The effect of Semax on functional connectivity of the resting state brain networks in healthy subjects. Hum Physiol. PMID: 32342318.
7. Zozulya AA, Neznamov GG, Siuniakov TS, et al. (2008). Efficacy and possible mechanisms of action of a new peptide anxiolytic drug Selank in the therapy of generalized anxiety disorders and neurasthenia. Zh Nevrol Psikhiatr Im S S Korsakova. 108(4):38-48. PMID: 18454096.

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Selank and Semax are sold by Peerless Peptides as research chemicals for in vitro and laboratory research by qualified researchers. They are not FDA-approved drugs, not for human or animal consumption, and not intended to diagnose, treat, cure, mitigate, or prevent any disease.