Semax vs Selank vs the Stack: Which Nootropic Peptide for Your Research Goal?
Semax, Selank and the combined stack compared: mechanism, evidence base and an honest assessment. The decision guide for nootropic research.
Semax and Selank are the two best-known Russian nootropic peptides and are often mentioned in the same breath. They pull in different directions, though: one stimulating and neurotrophic, the other calming and anxiolytic. This guide helps you choose between Semax alone, Selank alone and the combined stack, and gives an honest assessment of the evidence base.
For the mechanistic background of both peptides, see the Semax and Selank overview. This article is about the decision.
TL;DR: The quick decision
Semax: the stimulating, focus- and neurotrophic-oriented peptide (BDNF upregulation, dopaminergic modulation). Selank: the calming, anxiolytic peptide (positive allosteric GABA modulation). The stack (Semax + Selank): designed to be complementary, focus plus calm. Important: there is no dedicated study for the combination, the rationale is purely mechanistic.
Evidence note up front
Both peptides were developed in Russia and are only registered there as medicines, not in the US or the EU. The bulk of the literature comes from the same Russian research groups, often in Russian, without large independent Western placebo-controlled trials. Treat statements about efficacy in humans as preliminary.
For research purposes only
This text contextualizes research peptides. It is not medical advice, not a recommendation for use in humans, and does not replace consulting a physician. The study doses mentioned are the doses used in the literature, not a dosing recommendation.
Quick selection by research goal
Focus, drive, neuroprotection
Anxiety, calm, stress buffering
The options in detail
Semax: the stimulating, neurotrophic peptide
Semax is a synthetic heptapeptide, an analogue of the ACTH(4-10) fragment with an attached Pro-Gly-Pro for stabilization, without the corticotropic activity of the parent hormone. It is positioned as a focus- and neuroprotection-oriented nootropic.
Mechanistically:
- BDNF/TrkB upregulation: a single intranasal dose (50 µg/kg) increased BDNF protein and TrkB phosphorylation in the rat hippocampus [PMID 16996037].
- Neurotrophins after ischemia: Semax and its metabolite Pro-Gly-Pro activated the transcription of neurotrophins and their receptor genes after cerebral ischemia [PMID 19633950].
- Dopaminergic and serotonergic modulation: in animal models Semax enhanced amphetamine-induced striatal dopamine release and increased serotonin turnover, without being a direct agonist itself [PMID 16362768].
- Enkephalinase inhibition: Semax inhibits enkephalin-degrading enzymes in human serum [PMID 11443939].
Clinically, the strongest signal is stroke recovery: in a cohort of stroke patients, Semax (6000 µg/day) accelerated functional recovery and increased plasma BDNF [PMID 29798983]. The characteristic route is intranasal. Note: this signal comes from Russian literature and was not placebo-controlled and blinded.
Brain-boosting nootropic peptide derived from ACTH. Increases BDNF (brain-derived neurotrophic factor), enhances focus, memory, and mental clarity. Widely used in Russian clinical practice for cognitive enhancement.
Selank: the calming, anxiolytic peptide
Selank is a synthetic heptapeptide, an analogue of the immunomodulatory tetrapeptide Tuftsin with a stabilizing Pro-Gly-Pro tail. It is positioned as a calming, anxiolytic nootropic and is registered in Russia for anxiety disorders.
Mechanistically:
- GABAergic modulation (anxiolytic core): Selank acts as a positive allosteric modulator of GABA binding in brain membranes [PMID 30255741] and alters the expression of GABAergic genes in the rat frontal cortex [PMID 26924987].
- Serotonergic modulation: Selank increased serotonin metabolism in the brainstem, unlike the parent Tuftsin [PMID 19803361].
- BDNF/neurotrophic: Selank regulated BDNF content in the hippocampus and prefrontal cortex [PMID 31625062].
- Enkephalinase inhibition: together with Semax, Selank inhibits enkephalin-degrading enzymes in human serum [PMID 11443939].
The strongest human signal is anxiety: as an add-on to a benzodiazepine, Selank accelerated the onset of the anxiolytic effect and reduced its side effects [PMID 26356395]. Here too: small study, Russian literature, add-on therapy and not placebo-controlled monotherapy. The characteristic route is intranasal.
Synthetic tuftsin analog with anxiolytic, nootropic, and immunomodulatory properties. Developed at the Russian Academy of Sciences.
The stack: Semax + Selank
The idea behind the stack is mechanistic complementarity: Semax provides drive, focus and neurotrophic support, while Selank's GABAergic anxiolysis buffers the overstimulation, that is, balanced focus. Both also share enkephalinase inhibition and influence BDNF.
Important: no combination study
For the joint administration of Semax and Selank as a stack, there is no study in the indexed literature that administered the combination and measured its effect. Works that mention both test them separately. The stack rationale is therefore purely complementary-mechanistic, not a demonstrated combination effect. This should not be over-interpreted.
Pre-mixed combination of the two leading nootropic peptides in one vial. Semax boosts focus and BDNF, Selank reduces anxiety and enhances calm. Together they provide balanced cognitive enhancement for research.
Direct comparison at a glance
| Property | Semax | Selank | Stack (Mix) |
|---|---|---|---|
| Class | ACTH(4-10) analogue | Tuftsin analogue | Combination of both |
| Orientation | Stimulating, neurotrophic | Calming, anxiolytic | Balanced |
| Core mechanism | BDNF/TrkB, dopamine/serotonin [16996037, 16362768] | Allosteric GABA modulation [30255741] | Complementary |
| Strongest human signal | Stroke recovery [29798983] | Anxiety (add-on) [26356395] | None (no combination study) |
| Administration | Intranasal | Intranasal | Intranasal |
| Evidence base | Russian literature, not blinded | Russian literature, small | Mechanistic rationale only |
Honest evidence ranking
From the strongest to the weakest evidence: Semax in stroke recovery and Selank in anxiety (both with a human signal, but Russian literature and not as blinded monotherapy), then the cognitive effects of both (strong animal mechanistics, thin human data), and finally the Semax-plus-Selank stack at the bottom tier, because no direct combination evidence base exists for it.
Which option fits which goal?
Focus, drive, neuroprotection
Semax. The stimulating, neurotrophic direction with BDNF upregulation and the strongest human signal in stroke recovery [PMID 16996037, 29798983].
Anxiety, calm, stress buffering
Selank. The anxiolytic direction via positive allosteric GABA modulation, with a human signal as a benzodiazepine add-on [PMID 30255741, 26356395].
Balanced focus without overstimulation
The stack. Complementary mechanisms combined, with awareness that the combination itself has not been tested in a study.
Frequently asked questions
The substances described here are research peptides. This article serves knowledge transfer only, is not medical advice and is not to be understood as a recommendation for use in humans.
Research context for English-speaking buyers
Most of our English-speaking customers ship to the UK, Ireland, Malta or other English-as-second-language EU territories. The regulatory picture differs per country.
- Relevant authorities
- MHRA (UK, post-Brexit), HPRA (Ireland, EU-aligned), FDA Section 503A bulks list (US, restricted Cat 2 status of several peptides as of 2026)
- Customs and VAT
- EU shipments include 19% VAT; UK shipments after Brexit are now extra-EU and may attract UK VAT plus a handling fee at import
- Typical shipping window
- EU 2-4 working days, UK 4-7 working days, other international 7-14 working days, depending on customs
Research-grade peptides shipped from our EU warehouse are sold for laboratory use only and are not authorised for human or veterinary therapeutic application in any of the destination jurisdictions. US customers should be aware that the FDA Section 503A bulks list classification (and the April 2026 reclassification of twelve compounds) only governs compounding pharmacies, not direct-to-researcher imports for non-clinical work. UK buyers should declare the consignment on import and may be asked for a research justification by HMRC. We provide a CoA per batch identified by colour code rather than serial number; customs sometimes asks for this document when clearing the parcel.