Semax vs Selank: What the Research Shows

Semax and Selank are sibling peptides from the same Moscow institute, registered as drugs in Russia and sold elsewhere as research chemicals. Semax is an ACTH fragment studied for stroke and cognition; Selank is a tuftsin analog studied for anxiety. Here is what the published studies actually measured — and how thin the human evidence is outside Russia.

Semax and Selank are related Russian peptides aimed at different targets: Semax is a fragment of the stress hormone ACTH, studied mainly for stroke recovery and cognition, while Selank is built on the immune peptide tuftsin and studied mainly for anxiety. Both came out of the Institute of Molecular Genetics of the Russian Academy of Sciences, both are given intranasally in the published studies, and both are registered medicines in the Russian Federation^1,6. Outside Russia they are unapproved research chemicals. The honest summary of the evidence is short: interesting rodent biology, a handful of small Russian clinical studies, and almost no independent Western trials. This guide goes through what each study actually measured. Our Semax reference page covers the compound in more depth.

Semax vs Selank at a glance

Where they come from

A 2022 review of peptide drug development in Russia lists 14 peptide products registered in the Russian Federation, including Semax (classified as a nootropic) and Selank (an anxiolytic)¹. The review credits Semax to scientists at the Institute of Molecular Genetics working under academicians I. P. Ashmarin and N. F. Myasoedov, and describes it as an analog of the ACTH(4–10) fragment used to treat ischemic stroke¹. Selank was designed at the same institute together with the V. V. Zakusov Research Institute of Pharmacology⁶.

The shared design idea is visible in the sequences. Each starts from a short natural fragment — the ACTH(4–7) core in Semax, tuftsin in Selank — and adds Pro-Gly-Pro at the end. The Selank authors state that the tail was added to improve metabolic stability and prolong the drug's action⁶. Researchers from these groups frequently describe Semax as 'ACTH(4–7)PGP'⁴. One point worth noting when reading the literature: many of the same authors, Myasoedov among them, appear on both the mechanistic and the clinical papers^{3,4,6,7,8,9,10}. That is normal for a drug developed inside one institute, but it means the evidence has had little independent replication.

What the Semax research shows

Animal and cell studies

The best-developed idea about Semax is that it works through brain-derived neurotrophic factor (BDNF), a protein involved in neuron survival and synaptic plasticity. In rats, intranasal Semax at 50 and 250 µg/kg raised BDNF levels in the basal forebrain within 3 hours but not in the cerebellum, and labeled Semax bound specifically to membranes from that brain region². A second rat study found a single 50 µg/kg dose raised hippocampal BDNF protein up to about 1.4-fold and activation of its receptor trkB about 1.6-fold, and treated rats performed more conditioned avoidance responses in a learning test³. In a rat model of stroke (transient middle cerebral artery occlusion), RNA sequencing found 394 genes expressed differently in Semax-treated animals 24 hours later; Semax suppressed inflammation-related genes and activated neurotransmission-related ones⁴.

Human studies

The clinical work we found is Russian-language and focuses largely on stroke. A representative 2018 study followed 110 patients after ischemic stroke, split into early and late rehabilitation groups and then into subgroups that did or did not receive Semax. The Semax regimen was two 10-day courses of 6,000 mcg per day with a 20-day gap. Patients given Semax had higher plasma BDNF, and Semax together with high BDNF was associated with faster improvement on the Barthel index of daily functioning⁵. The abstract does not describe randomization, blinding or a placebo⁵, so it cannot separate the effect of Semax from differences between the groups.

What the Selank research shows

Animal studies

Selank research centers on the GABA system, the same inhibitory neurotransmitter system that benzodiazepines act on. In rat frontal cortex, a single intranasal dose of Selank (300 µg/kg) changed the expression of 45 of 84 neurotransmission-related genes at 1 hour and 22 at 3 hours, with a pattern that correlated with the effect of GABA itself⁶. Receptor-binding experiments suggest Selank acts as an allosteric modulator of GABA receptors, with binding sites that appear to differ from those of benzodiazepines such as diazepam⁷. The researchers argue this explains why Selank looks like a mild tranquilizer in animals; that remains a hypothesis built on rodent tissue.

Human studies

Three Russian clinical studies carry most of the weight. In 2008, 62 patients with generalized anxiety disorder or neurasthenia received either Selank (30 patients) or the benzodiazepine medazepam (32); the anxiolytic effects were reported as similar, with Selank also showing 'antiasthenic and psychostimulant' effects⁸. A 2014 study compared Selank with the benzodiazepine phenazepam in 60 patients with phobic-anxiety and somatoform disorders and reported a pronounced anxiolytic effect lasting about a week after the last dose⁹. A 2015 study gave 30 patients phenazepam alone and 40 patients phenazepam plus Selank, reporting fewer phenazepam side effects — such as memory impairment and sedation — in the combination group¹⁰.

None of the three abstracts mentions randomization, blinding or a placebo arm^8,9,10. Comparing a new drug only against an active comparator, without blinding, can show that the two behaved similarly in that clinic; it cannot show that the new drug beats placebo. The Selank authors also cite earlier clinical studies, from 1990 and 1998, for the claim that Selank matches low-dose tranquilizers without benzodiazepine side effects such as dependence and withdrawal⁶.

The human evidence side by side

This is what 'limited human evidence' looks like in practice: real patients, real outcomes, but small groups, open designs, one country and one research network. It is enough to justify a proper trial. It is not enough to say either peptide works for the uses people search for, or to set a dose.

Routes and dosing: what's documented

Both peptides are studied intranasally. The animal studies above all used nasal administration^2,6, and the Selank authors describe the nasal route as the best way to deliver the peptide to the central nervous system⁶. The only human dose we could verify from a primary source is the Semax stroke regimen — 6,000 mcg per day in two 10-day courses⁵ — which comes from a hospital setting after stroke, not from use as a cognitive enhancer. We did not find a verifiable human dose for Selank in the abstracts we reviewed, so we don't give one. Injectable use of either peptide has no human study behind it that we could locate. For why the route changes how much of a peptide reaches the body, see How to take peptides.

Regulatory status outside Russia

Neither Semax nor Selank is approved by the FDA. FDA's page on compounding substances that may present significant safety risks lists both — in the section for substances whose nominations were withdrawn — with the same warning: compounded products may pose a risk of immunogenicity for certain routes of administration because of possible aggregation and peptide-related impurities. For Selank, FDA says it lacks important information about safety in humans; for Semax, that it has no or limited safety information for the proposed routes and so cannot know whether the drug would cause harm¹¹.

Semax was then placed on the agenda of FDA's Pharmacy Compounding Advisory Committee for 24 July 2026, for proposed uses in cerebral ischemia, migraine and trigeminal neuralgia¹². Selank was not on that agenda. Advisory committees make non-binding recommendations, and at the time of writing we have not seen an FDA decision on Semax that follows from that meeting — check the committee page for the current position¹².

What nobody knows yet

1. Whether either peptide beats placebo in a randomized, double-blind trial — for any outcome.
2. Whether Semax improves cognition in healthy adults, the main reason it is bought outside Russia.
3. Long-term safety beyond short treatment courses, and safety with repeated or continuous use.
4. How much of an intranasal dose reaches the brain or the blood in humans, and how that varies between people.
5. What is actually in a vial sold as a research chemical — content, purity and sterility are unverified, which is exactly the concern FDA raises.

If you're weighing either peptide, the useful questions for a clinician are the same as for any unapproved compound — see Are peptides safe? This guide summarizes published research; it is not a recommendation or dosing advice.

FAQ

References

Primary sources — PubMed / NEJM / The Lancet.

1. Deigin VI, Poluektova EA, Beniashvili AG, Kozin SA, Poluektov YM. Development of Peptide Biopharmaceuticals in Russia. Pharmaceutics. 2022;14(4):716. https://pmc.ncbi.nlm.nih.gov/articles/PMC9030433/
2. Dolotov OV, Karpenko EA, Seredenina TS, et al. Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain. J Neurochem. 2006;97 Suppl 1:82-86. https://pubmed.ncbi.nlm.nih.gov/16635254/
3. Dolotov OV, Karpenko EA, Inozemtseva LS, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006;1117(1):54-60. https://pubmed.ncbi.nlm.nih.gov/16996037/
4. Filippenkov IB, Stavchansky VV, Denisova AE, et al. Novel Insights into the Protective Properties of ACTH(4-7)PGP (Semax) Peptide at the Transcriptome Level Following Cerebral Ischaemia-Reperfusion in Rats. Genes (Basel). 2020;11(6):681. https://pmc.ncbi.nlm.nih.gov/articles/PMC7350263/
5. Gusev EI, Martynov MY, Kostenko EV, Petrova LV, Bobyreva SN. [The efficacy of semax in the treatment of patients at different stages of ischemic stroke]. Zh Nevrol Psikhiatr Im S S Korsakova. 2018;118(3 Vyp 2):61-68. In Russian. https://pubmed.ncbi.nlm.nih.gov/29798983/
6. Volkova A, Shadrina M, Kolomin T, et al. Selank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission. Front Pharmacol. 2016;7:31. https://pmc.ncbi.nlm.nih.gov/articles/PMC4757669/
7. Vyunova TV, Andreeva L, Shevchenko K, Myasoedov N. Peptide-based Anxiolytics: The Molecular Aspects of Heptapeptide Selank Biological Activity. Protein Pept Lett. 2018;25(10):914-923. https://pubmed.ncbi.nlm.nih.gov/30255741/
8. Zozulia AA, Neznamov GG, Siuniakov TS, et al. [Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the therapy of generalized anxiety disorders and neurasthenia]. Zh Nevrol Psikhiatr Im S S Korsakova. 2008;108(4):38-48. In Russian. https://pubmed.ncbi.nlm.nih.gov/18454096/
9. Medvedev VE, Tereshchenko ON, Israelian AIu, et al. [A comparison of the anxiolytic effect and tolerability of selank and phenazepam in the treatment of anxiety disorders]. Zh Nevrol Psikhiatr Im S S Korsakova. 2014;114(7):17-22. In Russian. https://pubmed.ncbi.nlm.nih.gov/25176261/
10. Medvedev VE, Tereshchenko ON, Kost NV, et al. [Optimization of the treatment of anxiety disorders with selank]. Zh Nevrol Psikhiatr Im S S Korsakova. 2015;115(6):33-40. In Russian. https://pubmed.ncbi.nlm.nih.gov/26356395/
11. U.S. FDA. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. Content current as of 04/22/2026. https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
12. U.S. FDA. July 23-24, 2026: Meeting of the Pharmacy Compounding Advisory Committee. https://www.fda.gov/advisory-committees/advisory-committee-calendar/july-23-24-2026-meeting-pharmacy-compounding-advisory-committee-07232026