Semax vs Selank: A Research Comparison
Semax and Selank are two Russian-developed synthetic heptapeptides that are frequently mentioned together, often studied in parallel, and sometimes assumed to be closely related. They share several structural features — both are seven-amino-acid peptides, both use a Pro-Gly-Pro C-terminal extension for enzymatic stability, and both were registered as medicinal products in Russia — but they derive from entirely different parent molecules and are studied in largely non-overlapping research contexts. This comparison walks through the origins, chemistry, research applications, and how they relate to each other in a research setting.
At a Glance
| Property | Semax | Selank |
|---|---|---|
| Parent molecule | ACTH (adrenocorticotropic hormone) fragment 4-7 | Tuftsin (endogenous immunomodulatory tetrapeptide) |
| Structure | Heptapeptide: Met-Glu-His-Phe-Pro-Gly-Pro | Heptapeptide: Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Molecular formula | C₃₇H₅₁N₉O₁₀S | C₃₃H₅₇N₁₁O₉ |
| Molecular weight | 813.94 g/mol | 751.87 g/mol |
| CAS number | 80714-61-0 | 129954-34-3 |
| Primary research heritage | Neurotrophic factors and cognitive research | Anxiolytic and immunomodulation research |
Origins: Shared Design Philosophy, Different Parents
Both compounds were developed in Russia during the late Soviet and post-Soviet period at institutions including the Institute of Molecular Genetics of the Russian Academy of Sciences. They share a design philosophy: take a short bioactive peptide fragment from a naturally occurring molecule, then extend it at the C-terminus with a Pro-Gly-Pro sequence to make it more resistant to enzymatic degradation and better able to reach the brain.
Semax is built on ACTH (adrenocorticotropic hormone). Specifically, it uses the ACTH 4-7 sequence (Met-Glu-His-Phe) with the Pro-Gly-Pro extension added. ACTH itself is a pituitary hormone with roles in stress response and steroidogenesis, but the ACTH 4-10 region has long been known to have neurotrophic activity independent of the hormonal effects of the full molecule.
Selank is built on tuftsin, a natural tetrapeptide (Thr-Lys-Pro-Arg) derived from the Fc region of IgG that has known immunomodulatory activity. Selank uses this tuftsin sequence with the same Pro-Gly-Pro C-terminal extension.
The result is two structurally similar peptides — both seven residues, both with the same stability extension — that carry entirely different biological heritages: neurotrophic vs immunomodulatory.
Areas of Research Investigation Compared
Semax
- Neurotrophic factor studies — BDNF and NGF expression in neuronal cell models
- Cognitive and memory research — learning and memory paradigms in rodent models
- Neuroprotection models — cerebral ischaemia and stroke models in rodents
- Melanocortin receptor pharmacology — interaction with the melanocortin receptor family
Selank
- GABAergic system studies — GABA-A receptor modulation in rodent anxiety models
- Neurotransmitter research — serotonergic and dopaminergic signalling in animal models
- Immunomodulation research — cytokine expression and immune cell activity
- BDNF signalling — preclinical studies overlapping with Semax research
The two overlap in only one clear area: BDNF signalling. Beyond that, Semax is studied primarily as a cognitive/neurotrophic tool and Selank primarily as an anxiolytic/immunomodulatory tool. Framing them as “similar peptides” based on their structure is not really accurate at the research-application level.
Key Differences
1. Biological pathway
Semax acts primarily through the melanocortin receptor family (inherited from its ACTH parent) and modulates neurotrophic factor expression as a downstream effect. Selank acts primarily through GABAergic and serotonergic pathways and retains some immunomodulatory activity inherited from its tuftsin parent. These are entirely different biological systems.
2. Research application
Semax’s research literature is dominated by cognitive, learning, and neuroprotection studies. Selank’s is dominated by anxiety and immunomodulation studies. Substituting one for the other in a research design would not be appropriate — they answer different questions.
3. Regulatory status
Both are registered as medicinal products in Russia (Semax has a longer registered clinical history there). Neither is approved by the MHRA, FDA, or any equivalent Western regulator for human or veterinary use.
4. Route of administration in research
Both peptides are frequently investigated via intranasal delivery in preclinical models — a route chosen because both molecules can cross the nasal epithelium and reach the brain. Standard bacteriostatic water reconstitution is compatible with intranasal research use.
Where They Overlap
The clearest overlap is in BDNF signalling — both peptides have been reported to modulate brain-derived neurotrophic factor expression in preclinical models, albeit through different upstream mechanisms. This is why the two are sometimes studied in combination in Russian neurological research, and why some research groups treat them as complementary tools rather than substitutes.
Product Specifications Compared
| Specification | Semax | Selank |
|---|---|---|
| Molecular formula | C₃₇H₅₁N₉O₁₀S | C₃₃H₅₇N₁₁O₉ |
| Molecular weight | 813.94 g/mol | 751.87 g/mol |
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Parent molecule | ACTH 4-7 | Tuftsin |
| Recommended solvent | Bacteriostatic water | Bacteriostatic water |
| Vial size (Revial Labs) | 10mg | 10mg |
| Purity | ≥99% HPLC verified | ≥99% HPLC verified |
Choosing Between Them in a Research Context
The choice is dictated by the research question rather than any notion of one being generally superior:
- Cognitive, learning, or neuroprotection research — Semax has the deeper literature.
- Anxiolytic or GABAergic research — Selank has the deeper literature.
- Immunomodulation research — Selank has a specific advantage due to its tuftsin heritage.
- BDNF signalling research — both are appropriate, and comparative studies exist.
- Investigating combined neurotrophic and anxiolytic effects — some research groups use both in parallel.
Frequently Asked Questions
Are Semax and Selank the same peptide with different names?
No. They are two structurally similar but distinct peptides. Both are heptapeptides with a Pro-Gly-Pro C-terminal extension, but the N-terminal four residues differ entirely, as do the parent molecules from which they derive (ACTH vs tuftsin).
Why do they share the Pro-Gly-Pro extension?
Both were designed by Russian research groups using the same stabilisation strategy — appending Pro-Gly-Pro at the C-terminus increases resistance to enzymatic degradation and improves the peptide’s ability to reach the brain. The choice reflects a shared design tradition rather than a shared biological function.
Can Semax and Selank be studied in combination?
Yes, and some Russian research groups have investigated combination effects. Because the two act on largely different biological pathways, combination studies can examine whether the effects are additive or interact in more complex ways.
Do both peptides use bacteriostatic water for reconstitution?
Yes. Both are typically reconstituted in bacteriostatic water. See How to Reconstitute Research Peptides for step-by-step guidance.
Products Referenced in This Comparison
Further Reading
Research Use Only
All products referenced in this article are supplied by Revial Labs for in vitro laboratory research use only. Not for human or veterinary use, not for use in food, cosmetics, or supplements, and not for diagnostic or therapeutic purposes. This article is a summary of published research directions and should not be interpreted as claims about either compound’s effects in humans. Neither compound is approved by the MHRA, FDA, or equivalent Western regulatory bodies.
