Semax and Selank are supplied strictly as laboratory research materials. They are not approved, intended or authorised for human consumption or any therapeutic use in this context. This article is written for qualified researchers and is not medical advice.
Two peptides from one programme
Semax and Selank are frequently paired because they share a lineage: both were developed concurrently at the Russian Academy of Sciences, both are seven-amino-acid peptides stabilised with the same Pro-Gly-Pro C-terminal motif, and both went on to regulatory registration inside Russia while remaining unapproved elsewhere. That common heritage is where the resemblance ends. Semax descends from a fragment of adrenocorticotropic hormone (ACTH) and is studied for nootropic and neurotrophic effects; Selank descends from the immune peptide tuftsin and is studied for anxiolytic and immunomodulatory effects. Put simply, the contrast is cognition and focus versus calm and anxiety. Here we put the two molecules side by side.
| Semax | Selank | |
|---|---|---|
| Peptide class | ACTH(4-10) analogue heptapeptide | Tuftsin analogue heptapeptide |
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Primary mechanism | BDNF modulation; dopaminergic & serotonergic signalling | GABAergic allosteric modulation; neuroimmune / cytokine signalling |
| Duration note | Serum half-life >1 h; bioactivity ~20–24 h in animal models | Short-acting peptide; intranasal route |
| Main research focus | Nootropic, neuroprotective, stroke models | Anxiolytic, anti-stress, neuroimmune |
| Regulatory status | Registered in Russia & Ukraine; not FDA/MHRA approved | Registered in Russia (2009); not FDA/MHRA approved |
Semax: the cognition and neurotrophic peptide
Semax is a synthetic heptapeptide derived from the ACTH(4-10) fragment, with a Pro-Gly-Pro tail bolted on to extend its bioactivity to roughly 20–24 hours in animal models — a substantial extension over the parent fragment, even though its measured serum half-life sits above an hour. Its sequence is Met-Glu-His-Phe-Pro-Gly-Pro. In research it is characterised as a nootropic and neuroprotective agent, and its most discussed signalling readout is BDNF: a single intranasal dose raised BDNF in rat basal forebrain within hours, and multi-course dosing elevated plasma BDNF in human stroke studies. Alongside that neurotrophic signature, Semax modulates monoamine neurotransmission, increasing serotonin and potentiating dopaminergic activity, which is why it is used in research paradigms that probe attention, learning and memory-consolidation markers.
Genome-wide transcriptomic work in ischaemic rat cortex added another layer: over half of Semax-modulated genes were immune-response related, with a cluster of vascular genes tied to endothelial migration — pointing to an immunomodulatory and pro-vascular basis for its neuroprotection. Semax is registered as a medicine in Russia and Ukraine for stroke, dyscirculatory encephalopathy and optic nerve atrophy, but it carries no FDA or MHRA approval and is supplied here purely as a research reagent. Researchers sourcing material can buy Semax UK at research grade with a COA, and the full mechanistic profile lives on the Semax knowledgebase page.
Selank: the anxiolytic and immunomodulatory peptide
Selank is a synthetic heptapeptide built on the natural immunomodulatory tetrapeptide tuftsin — a fragment of the IgG heavy chain — again extended with a Pro-Gly-Pro motif for stability. Its sequence is Thr-Lys-Pro-Arg-Pro-Gly-Pro. Where Semax leans cognitive, Selank leans calming: it was registered as a medical drug in Russia in 2009 as a 0.15% nasal solution for generalised anxiety disorder and neurasthenia, and its defining feature is anxiolysis without the sedation or muscle relaxation that characterises classical anxiolytics.
Mechanistically, Selank works mainly through the GABAergic system. Transcriptomic analysis of GABAergic genes in rat frontal cortex found a strong correlation between Selank's expression profile and that of GABA itself, supporting a model in which Selank allosterically raises GABA-A receptor affinity for endogenous GABA rather than acting as a direct agonist — a more physiological modulation than benzodiazepine-style receptor occupancy. Beyond that, Selank shifts cytokine and immunoglobulin expression, giving it a neuroimmune dimension that features in stress-signalling research. Material can be sourced as Selank research material, with the deeper profile on the Selank knowledgebase page.
What the differences mean in a research context
Read across the table and the two peptides look like mirror images built on a shared frame. Same length, same stabilising motif, same country of origin, same regulatory pattern — and yet opposite functional emphases, because they inherit from opposite parent molecules. Semax's ACTH lineage points it toward neurotrophic and monoaminergic signalling, making it the natural choice for research into cognition, neuroprotection and BDNF-linked plasticity. Selank's tuftsin lineage points it toward GABAergic and neuroimmune signalling, placing it in studies of anxiety, stress reactivity and immune-neurological crosstalk.
That divergence is exactly why the two are so often examined together rather than treated as substitutes. Their mechanisms barely overlap, so a study design can hold the peptide "family" constant while varying the pathway under investigation — cognition on one arm, calm on the other. It is also why researchers describe them as complementary: the focus-oriented profile of one and the anxiety-oriented profile of the other address different questions rather than competing to answer the same one. A note of caution belongs here too. Much of the supporting human data is Russian-language and tied to the registered indications in that jurisdiction; neither compound is approved by the FDA or MHRA, and preclinical findings do not establish safety or efficacy. The comparison describes distinct research profiles, not a ranking.
The bottom line
Semax and Selank share a birthplace and a scaffold but answer different questions: Semax is the ACTH-derived peptide for cognition, BDNF and neuroprotection, while Selank is the tuftsin-derived peptide for anxiolysis, anti-stress and neuroimmune signalling. Choose according to the pathway your work targets — or, as many do, study them together. For research-grade material, see our dedicated pages to buy Semax UK and buy Selank UK, each ≥99% purity with a COA.