In short
Semax and Selank are routinely discussed as a pair, and for good reason. Both came out of the same Russian research institute, both are stabilised by the same appended tripeptide, and both are studied in the central nervous system. They are not interchangeable. The essentials:
- Different parents: Semax derives from a fragment of ACTH, Selank from the immune peptide tuftsin
- Different contexts: Semax appears in neurotrophic and attention research, Selank in anxiety and withdrawal models
- Same stabiliser: both carry an appended proline-glycine-proline sequence that resists peptidase degradation
- Same limitation: the evidence base is largely Russian, western replications are scarce, and most behavioural studies use a contested route of administration
Everything below refers to published research and to sourcing material for laboratory purposes, not to use in humans.
What are the two molecules, structurally?
Semax is a synthetic analogue of the 4-10 fragment of adrenocorticotropic hormone, extended by a proline-glycine-proline sequence. Selank is a heptapeptide derived from tuftsin, an endogenous immune peptide, carrying the same PGP extension. The shared element is the stabiliser, not the active core. Their parent sequences come from entirely different biological systems, one endocrine and one immune.
That appended tripeptide matters more than it looks. Native peptide fragments are degraded quickly by peptidases, and without the extension neither molecule would survive long enough to be practical in a study. The stabiliser is what made both usable as research tools.
Semax was developed in the 1980s at the Institute of Molecular Genetics of the Russian Academy of Sciences. Selank came out of the same tradition, which explains why the two are so often presented together despite the difference in origin.
What has been published on Semax?
Semax research spans several mechanistic levels rather than converging on one. A 2011 study described changes in the expression of neurotrophic factors in rat brain following administration. More recent work has examined antidepressant-like and antistress effects in animal models, and a 2025 paper proposed involvement of the mu opioid receptor gene Oprm1. A 2025 review consolidates the current state and places the derivatives in context.
The specific publications are worth naming, because the field is small enough that a handful of papers carry most of the weight: Stavchansky 2011, Mol Biol; Inozemtseva 2024, Eur J Pharmacol; Liu 2025, Br J Pharmacol; and the review by Radchenko 2025, Acta Naturae.
What that list does not contain is a completed registration-relevant clinical trial. Semax is not approved as a medicine in the EU.
What has been published on Selank?
Selank is studied in a narrower band than Semax, concentrated on anxiety, stress and withdrawal models, with the described point of action in the GABAergic and serotonergic systems. A 2018 review covers the molecular aspects. Animal model work describes effects in ethanol-induced memory impairment and in morphine withdrawal aversion models.
The molecular groundwork is summarised in Vyunova 2018, Protein Pept Lett. The animal model literature includes Kolik 2019, Bull Exp Biol Med and Konstantinopolsky 2022, Bull Exp Biol Med.
Selank shares the regulatory status of its sibling. It is not an approved medicine anywhere in the EU.
Side by side
The two molecules differ in parent sequence and research context, and overlap in stabiliser, regulatory status and the limitations of their evidence base. Price per milligram is the only comparable commercial figure, because vials differ in content.
| Semax | Selank | |
|---|---|---|
| Derived from | ACTH(4-10) | Tuftsin |
| Parent system | Endocrine | Immune |
| Stabiliser | PGP extension | PGP extension |
| Research context | Neurotrophic factors, stress, attention | Anxiety, withdrawal, GABA system |
| Price per mg, 5 mg vial | 5.38 € | 5.38 € |
| Price per mg, 10 mg vial | 3.59 € | 3.59 € |
| Regulatory status | Not approved | Not approved |
The larger vial lowers the milligram price by roughly 30 percent in both cases. Product data and batch certificates are on the Semax and Selank pages.
Why the methodology matters more than the comparison
Two constraints apply to the entire literature on both molecules, and neither is usually mentioned in vendor summaries. The first is the blood-brain barrier. Peptides are comparatively large, charged molecules and do not cross it readily. What is taken for granted with a small molecule, that some fraction of the administered dose reaches the central nervous system, has to be demonstrated separately for a peptide.
The second constraint is the route. Most behavioural studies of both compounds use intranasal administration, and that route has been openly contested in neuropeptide research for years. The critique is best known from work on oxytocin, where the question of how much substance actually reaches the brain, and whether that amount explains the reported effects, was set out directly (Leng and Ludwig 2016, Biol Psychiatry). The same question applies here.
Add the origin of the data. The evidence base comes predominantly from Russian research, and independent western replications are rare. None of this means the findings are wrong. It means the confidence interval around them is wider than a summary table suggests.
The most methodologically interesting paper compares both compounds using a connectomic approach, attempting to tie described effects to measurable network changes rather than reporting them in isolation (Panikratova 2020, Dokl Biol Sci). That is the kind of work the field needs more of.
How to verify laboratory material
For a laboratory the practical question is not which of the two is more interesting, but whether the vial contains what the label claims. The number printed on the label is not evidence. The batch-specific certificate of analysis is.
| Check | What it establishes |
|---|---|
| Batch-specific CoA | Applies to the actual lot, not a generic sample document |
| HPLC purity | Describes chromatographic purity, not peptide content by mass |
| LC-MS identity | Confirms the molecule is the one on the label |
| Independent laboratory | Analysis separate from the manufacturer, Molequa® batches are verified by Janoshik Analytical |
Both compounds ship as lyophilised powder, are sensitive to temperature and moisture, and are stored at 2 to 8 °C protected from light.
What this article deliberately omits
No dosing schedules, no administration protocols, no recommendations for use in humans. Neither compound is an approved medicine, and both are sold exclusively as reference material for laboratory research.
Every reference above points to a real, verifiable publication. When a summary attributes an effect to a peptide and cannot name a source for it, that absence is itself information about the source.
Frequently asked questions
What is the difference between Semax and Selank? They derive from different parent sequences. Semax is a synthetic analogue of the ACTH 4-10 fragment, from the endocrine system. Selank is a heptapeptide derived from tuftsin, an endogenous immune peptide. Both carry the same appended proline-glycine-proline sequence, which is a stabiliser rather than an active core.
What is each compound studied for? Semax appears in research on neurotrophic factors, stress and attention (Stavchansky 2011, Mol Biol; Radchenko 2025, Acta Naturae). Selank is studied in a narrower band covering anxiety, stress and withdrawal models, with the described point of action in the GABAergic and serotonergic systems (Vyunova 2018, Protein Pept Lett).
Why is the intranasal route methodologically contested? Most behavioural studies of both compounds use intranasal administration. Peptides are comparatively large, charged molecules and do not cross the blood-brain barrier readily, so the question of how much substance reaches the brain, and whether that amount explains the reported effects, has to be answered separately. The critique is best known from oxytocin research (Leng and Ludwig 2016, Biol Psychiatry).
How strong is the evidence base? It is limited. The literature comes predominantly from Russian research, independent western replications are rare, and there is no completed registration-relevant clinical trial for either compound. The most methodologically advanced work compares both using a connectomic approach (Panikratova 2020, Dokl Biol Sci).
Are Semax and Selank approved medicines? No. Neither is registered as a medicine in the EU. Molequa® sells both exclusively as reference material for scientific laboratory research, not for use in humans, not as a food supplement and not as a cosmetic.
What does each cost per milligram? Semax is 5.38 € per mg in the 5 mg vial and 3.59 € per mg in the 10 mg vial. Selank is 5.38 € per mg in the 5 mg vial and 3.59 € per mg in the 10 mg vial. The larger vial lowers the milligram price by roughly 30 percent for both.
How do I verify the material before buying? Ask for the batch-specific certificate of analysis with lot number, analysis date, HPLC purity and mass spectrometry identity confirmation. HPLC purity describes chromatographic purity, not peptide content by mass, so the number alone is not sufficient. Molequa® batches are verified by the independent laboratory Janoshik Analytical.
