For research purposes only. Not for human consumption or therapeutic use. Neither Selank nor Semax is approved by the FDA or EMA.
Selank and Semax are two synthetic peptides developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. Both are built from short native regulatory sequences. Both are studied intranasally. And both are often labeled “nootropic peptides” in the literature, though that label describes a research context, not a clinical outcome.
This guide compares the two side by side. It covers sequences, mechanisms, administration routes, the Russian research tradition that produced most of the primary literature, and how researchers commonly investigate the pair together in preclinical models.
Selank vs Semax at a glance
Selank and Semax are frequently discussed in the same breath. They are not the same molecule. They do not share a parent peptide. And their proposed mechanisms act on different receptor systems. The table below summarizes the key differences.
| Property | Selank | Semax |
|---|---|---|
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Met-Glu-His-Phe-Pro-Gly-Pro |
| Parent peptide | Tuftsin (immunomodulatory tetrapeptide) | ACTH(4-10) fragment (neurotrophic) |
| Molecular weight | ~751 Da | ~813 Da |
| Primary proposed mechanism | GABAergic modulation, enkephalin metabolism | BDNF/NGF expression, MAPK/ERK signaling |
| Key research areas | Anxiolytic-like behavior, immune signaling | Cerebrovascular models, cognitive endpoints |
| Research administration route | Intranasal, subcutaneous | Intranasal, subcutaneous |
| Methionine residue | No | Yes (Met1, oxidation sensitive) |
| Origin lab | Institute of Molecular Genetics, Moscow | Institute of Molecular Genetics, Moscow |
Origins: two peptides from the same Russian tradition
Both peptides emerged from the same research program in Moscow. Selank was designed from tuftsin, a naturally occurring tetrapeptide released from IgG heavy chain cleavage. Tuftsin is known for its immunomodulatory effects. Adding a C-terminal Pro-Gly-Pro extension produced Selank, a heptapeptide with improved metabolic stability.
Semax took a different parent. Early studies of adrenocorticotropic hormone (ACTH) found that the ACTH(4-10) fragment retained neurotrophic activity independent of adrenal steroid release. Researchers trimmed and modified that fragment, then applied the same Pro-Gly-Pro stabilization trick. The result was Semax.
This shared lineage matters for researchers. Both peptides share the same C-terminal extension. Both were developed to resist aminopeptidase degradation. And both are designed around the idea that short peptides can carry the regulatory signal of much larger parent molecules.
Selank mechanism of action
Selank has been studied primarily in the context of anxiety-like behavioral models and immune signaling. Its proposed mechanisms involve several distinct pathways.
GABAergic modulation
Published research suggests Selank may influence the GABAergic system. Studies in animal models have reported changes in GABA-A receptor subunit expression after Selank administration. Unlike benzodiazepines, which bind GABA-A receptors directly, Selank appears to act through indirect modulation. The exact receptor-level interaction is still under investigation.
BDNF expression
Brain-derived neurotrophic factor (BDNF) is a key neurotrophin involved in synaptic plasticity. Several preclinical studies have reported associations between Selank administration and altered BDNF mRNA expression in specific brain regions. These are mRNA-level observations. They should not be read as direct evidence of protein-level functional change.
Enkephalin metabolism
Selank has been reported to inhibit enzymes involved in enkephalin degradation. This would potentially prolong endogenous opioid peptide signaling without direct opioid receptor binding. This mechanism is distinct from classical opioid pharmacology and remains an active area of investigation.
Semax mechanism of action
Semax research focuses on neurotrophic factor regulation and cerebrovascular endpoints. Its proposed mechanisms are different from Selank’s.
Neurotrophic factor upregulation
Published research associates Semax administration with increased expression of BDNF, nerve growth factor (NGF), and glial cell line-derived neurotrophic factor (GDNF) in preclinical models. These effects appear to operate independently of melanocortin receptor binding, despite Semax’s parent sequence deriving from ACTH. The signaling downstream is reported to involve MAPK/ERK cascades.
Cerebrovascular preclinical models
Semax has been studied in animal models of cerebral ischemia. Published reports describe associations with reduced infarct volume and altered neurological scores in these models. These findings are limited to rodent models and should not be extrapolated to human clinical outcomes.
Transcriptomic effects
Gene expression studies in the rat brain have reported that Semax administration affects hundreds of genes. The pathways involved span immune response, neurotransmission, and vascular function. This breadth is consistent with a peptide acting upstream of multiple signaling cascades rather than at a single receptor.
The Pro-Gly-Pro extension
Both peptides share the C-terminal Pro-Gly-Pro tripeptide. This is not an accident of design. The extension reduces susceptibility to aminopeptidase cleavage, extending the functional window in biological systems.
Pro-Gly-Pro (PGP) is also biologically active on its own. It has been independently studied in neutrophil chemotaxis and inflammatory signaling. Whether the Pro-Gly-Pro tail contributes to the Selank and Semax profile, or acts purely as a metabolic shield, remains an open question. Researchers designing dose-response studies should be aware of this ambiguity.
Intranasal administration in research
Intranasal delivery is the dominant research route for both Selank and Semax. This is not a matter of convenience. It is a direct consequence of the molecular properties of these peptides.
Short peptides like Selank and Semax face two problems with systemic delivery. First, they are rapidly cleaved by peptidases in plasma. Second, they do not readily cross the blood-brain barrier when administered subcutaneously. Intranasal administration bypasses both problems. It delivers peptide directly to the olfactory and trigeminal nerve pathways, providing a route into the central nervous system that avoids first-pass metabolism.
For researchers, this has practical implications. Typical intranasal concentrations in published protocols range from 0.1 to 1.0 mg/mL. Reconstituted solutions are transferred to sterile nasal spray bottles. Dosing volumes are small (often 50 microliters per nostril). Subcutaneous administration is also used, particularly for kinetic studies where systemic exposure is the endpoint. See our guide on intranasal vs subcutaneous bioavailability for a broader comparison.
Russian neuroscience tradition and Western replication
Most primary literature on Selank and Semax comes from Russian institutions. The Institute of Molecular Genetics, the Institute of Experimental Medicine, and associated groups have published the majority of peer-reviewed work on both peptides. Journals like Bulletin of Experimental Biology and Medicine and Neuroscience and Behavioral Physiology carry many of these findings.
Western replication has been limited. This is partly a funding pattern. Neither peptide has a Western commercial sponsor pursuing clinical development. It is also partly a regulatory pattern. Both compounds are approved as pharmaceuticals in Russia but lack EMA or FDA authorization. The asymmetry means researchers working with Selank or Semax should cross-reference original Russian sources rather than relying solely on English-language reviews. PubMed indexes many of these papers, but not all.
This same dynamic appears with other peptides from the Russian regulatory peptide tradition, including those covered in our neuroprotective peptides in longevity research guide.
Stacking Selank and Semax in research
Researchers frequently investigate Selank and Semax together. The rationale is straightforward. The two peptides have distinct proposed mechanisms. Selank is studied for GABAergic and immune endpoints. Semax is studied for neurotrophic and cognitive endpoints. Co-administration lets researchers probe whether the effects are additive, synergistic, or independent.
Published preclinical studies have examined the pair in behavioral models and in molecular marker panels. Results vary by model and endpoint. Researchers designing stacking protocols should plan for separate vehicle controls, interaction terms in their statistical model, and careful dose-matching between peptides.
Handling and storage
Both peptides are supplied as lyophilized powders. Reconstitution uses bacteriostatic water. Unreconstituted vials are stored at -20 C. Once reconstituted, solutions are kept at 2-8 C and typically used within 21-28 days.
Semax has one additional handling concern. Its N-terminal methionine (Met1) is susceptible to oxidation. Light, heat, and trace metal ions accelerate this. Amber vials and foil wrapping are standard precautions. Selank lacks methionine and is somewhat more stable under comparable conditions.
For quality control, researchers should verify purity by HPLC (>=98 percent) and confirm the correct molecular weight by mass spectrometry. Residual trifluoroacetic acid from synthesis can affect pH-sensitive experiments and should be documented on the certificate of analysis. For broader terminology, see our peptide research terminology glossary.
Frequently asked questions
Is Selank the same as Semax?
No. They are two different synthetic peptides with different sequences, different parent molecules, and different proposed mechanisms. Selank derives from tuftsin and is studied for GABAergic and immune effects. Semax derives from an ACTH fragment and is studied for neurotrophic factor expression. They share only the C-terminal Pro-Gly-Pro stabilization extension and the same originating research tradition.
How are Selank and Semax administered in research?
Both peptides are predominantly administered intranasally in preclinical studies. This route bypasses first-pass metabolism and provides direct nose-to-brain delivery via olfactory and trigeminal pathways. Subcutaneous administration is also used, particularly for pharmacokinetic studies. Typical intranasal research concentrations range from 0.1 to 1.0 mg/mL.
What is the molecular weight of Selank?
Selank has a molecular weight of approximately 751 Da. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro. Mass spectrometry is the standard verification method, and research-grade material should be cross-checked against the expected monoisotopic mass.
Does Semax cross the blood-brain barrier?
When delivered intranasally, Semax is reported to reach central nervous system tissue via olfactory and trigeminal nerve pathways, which is a different route from classical blood-brain barrier transport. Systemic delivery faces the usual peptidase and barrier challenges short peptides encounter. Published research has examined both routes.
Are Selank and Semax FDA approved?
No. Neither Selank nor Semax has FDA or EMA approval. Both are approved as pharmaceuticals in Russia, where they were developed at the Institute of Molecular Genetics. In the EU and US they are available only for research use as synthetic peptides. They are not approved drugs for any human indication in these jurisdictions.
Can Selank and Semax be stacked in research protocols?
Yes, and many published studies co-administer the two peptides. Their distinct proposed mechanisms (GABAergic versus neurotrophic) make them a natural pair for preclinical work that wants to probe multiple pathways in one experiment. Researchers planning stacking protocols should include separate vehicle controls and dose-match carefully.
Research-grade material from CertaPeptides
CertaPeptides supplies both peptides as research vials with >=99 percent HPLC purity and batch-specific certificates of analysis. Available formats include Selank 5 mg, Selank 10 mg, Semax 5 mg, Semax 10 mg, and a combined Semax + Selank Blend 20 mg for researchers running stacking protocols.
Strictly for research purposes only. Not for human consumption or therapeutic use. Neither compound is approved by the FDA or EMA for any clinical indication. The term “nootropic” in this article describes a research context, not a clinical outcome or medical claim.
References
- Uchakina ON, et al. (2008). Immunomodulatory effects of Selank in patients with anxiety-asthenic disorders. Bulletin of Experimental Biology and Medicine, 145(2), 225-227. PMID: 18577280.
- Ashmarin IP, et al. (1997). Regulatory peptides in cognitive processes. Neuroscience and Behavioral Physiology, 27(3), 261-267. PMID: 9469267.
- Medvedev VE, et al. (2013). Anxiolytic effect of Selank and its metabolites. Bulletin of Experimental Biology and Medicine, 156(2), 163-166. PMID: 23847065.
- Eremin KO, et al. (2004). Semax and Selank affect the behavior of rats in the open field test. Bulletin of Experimental Biology and Medicine, 137(3), 257-260. PMID: 15232644.
- Kozlovskii II, Danchev ND. (2003). Optimizing effects of cortexin and Semax on the learning and memory processes in rats. Neuroscience and Behavioral Physiology, 33(4), 369-372. PMID: 12783168.