what is the difference
Semax and selank
Two peptides of the same length from the same laboratory, built on unrelated starting fragments, and sold so consistently as a pair that their abbreviations have started trading places.
Semax is a seven amino acid peptide built from ACTH(4-10), a short stretch of adrenocorticotropic hormone, with a proline-glycine-proline tail attached to slow its breakdown in blood. The change takes away the hormonal activity the parent carries. Selank is also seven amino acids and carries the same tail, but its starting fragment is tuftsin, a four amino acid piece released from the heavy chain of immunoglobulin G that signals to immune cells.
Both came out of the Institute of Molecular Genetics in Moscow, both are registered medicines in Russia, and both are sold into the same audience, usually side by side. That closeness is where the trouble starts: the N-acetylated amidate forms are abbreviated NASA for semax and NAS for selank, one letter apart, and vendor listings swap them. This page sets out what each substance is, what its own record contains, and which facts belong to which molecule.
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The short answer
Semax and selank are different peptides with different parents. Semax descends from a stress hormone fragment with the hormonal activity engineered out; selank descends from tuftsin, an immune-signalling fragment. The proline-glycine-proline tail they share is a stability trick applied to both, not a family relationship.
Their published records are also different shapes. On 2 August 2026 the registry returned no study of semax at all, under its own name, under N-acetyl semax, or under Semax ACTH; selank returned 10, largely non-interventional or Russian-sponsored, and none of them tests the anxiety use it is marketed for [7]. What exists for semax in people is two Russian-language stroke reports indexed in PubMed [1] [2]. What exists for either in the use it is actually sold for is rodent behaviour and rodent biochemistry [3] [4] [6].
Side by side
| Property | Semax | Selank |
|---|---|---|
| What it is | A seven amino acid peptide: ACTH(4-10) with a proline-glycine-proline tail attached | A seven amino acid peptide: tuftsin with the same proline-glycine-proline tail attached |
| Parent fragment | Adrenocorticotropic hormone, residues 4 to 10. The modification removes the hormonal activity the parent carries | Tuftsin, a four amino acid fragment released from the heavy chain of immunoglobulin G that signals to immune cells |
| Abbreviation of the N-acetyl amidate form | NASA, for N-acetyl semax amidate | NAS, for N-acetyl selank amidate. One letter apart, and vendor listings swap them |
| Other names in circulation | ACTH(4-10) analog | TP-7, which is the name the published rat work uses [4] |
| What it is marketed for | Focus, memory, and recovery after brain injury | Anxiety and stress |
| Registered human trials | 0 on 2 August 2026, under semax, under N-acetyl semax and under Semax ACTH [7] | 10 on 2 August 2026, largely non-interventional or Russian-sponsored, and none testing the marketed use [7] |
| Published human literature indexed in PubMed | Two Russian-language reports in the same journal, both in stroke populations: a 1997 clinical and electrophysiological study in the acute period of hemispheric ischaemic stroke [1] and a 2018 study of patients at different stages of ischaemic stroke [2] | None found for this page. The published work is rodent behaviour and rodent biochemistry [4] [5] [6] |
| Published work behind the marketed use | Rodent. Semax was reported to change BDNF and trkB expression in the rat hippocampus [3] | Rodent. Long-term treatment with the tuftsin analog TP-7 and anxiety-phobic behaviour in rats [4], a review of the tuftsin family in stress-related behaviour [5], and hippocampal and prefrontal BDNF content in rats after ethanol exposure [6] |
| Status in Russia | A registered medicine | A registered medicine |
| US approval status | No approved application returned by a query of FDA's approved-products data on 2 August 2026 [10] | No approved application returned by the same query on the same date [10] |
| FDA 503A position | Semax-related bulk drug substances went before the Pharmacy Compounding Advisory Committee on 24 July 2026, as two voting questions covering the free base and the acetate [8] [9] | Not among the seven substances put to that committee on 23 and 24 July 2026 [9] |
Why the two get mixed up
The abbreviation is the mechanism. N-acetyl semax amidate compresses to NASA and N-acetyl selank amidate compresses to NAS, and those two strings differ by a single character in a category where product names are already dense with hyphens and numbers. A listing that drops or gains one letter names a different molecule, and nothing in the surrounding copy would tell a reader that it had happened.
Everything around the names reinforces the collapse. The two peptides are the same length. They were developed at the same institute. They carry the same proline-glycine-proline tail, added for the same reason. They are registered as medicines in the same country and are unapproved in the same one. They are sold together, discussed together, and reviewed together in the same community threads.
What does not carry across is the part that matters. Semax starts from a piece of a stress hormone and selank starts from a piece of an antibody, so their parents belong to different systems entirely. A result about one is not a result about the other, and the shared tail is a chemical stabiliser rather than evidence of a shared mechanism. Where this site reports a study, it names the molecule the study actually gave.
What the published record covers for each
The two records differ most in what a registry search returns. Semax returned nothing on 2 August 2026, under its own name and under both aliases, so nothing currently registered anywhere is capable of changing what is known about it; the human material that exists is two Russian-language reports in the same journal, both in stroke, with design detail not available in the English-language record [Human open-label] [1] [2] [7]. Both are in a population nobody buys the peptide for, and both come from the institute that developed it.
The work behind the focus and memory use is in rats: semax was reported to regulate BDNF and trkB expression in the hippocampus, which is a measurement of gene and protein expression in brain tissue rather than a behavioural outcome [Animal] [3]. Mechanism in a rodent does not establish an effect in people.
Selank's 10 registrations read like a programme until they are opened. They are largely non-interventional or Russian-sponsored, and none of them tests the anxiety use the peptide is sold for, on a ClinicalTrials.gov search run for this page on 2 August 2026 [7]. The published basis for that use is rat behaviour: long-term treatment with the tuftsin analog TP-7 measured against anxiety-phobic behaviour and body weight [4], a review collecting the tuftsin family work in stress-related behaviour [5], and a study reporting BDNF content in the rat hippocampus and prefrontal cortex after ethanol exposure [6] [Animal].
One comparison people make for selank deserves stating precisely, because of how it is usually phrased. Selank is described as producing no dependence signal of the kind associated with benzodiazepines. That description rests on rodent behavioural work and on Russian-language reports rather than on a controlled human comparison, and an absent report is a different thing from a measured finding. No study set the two against each other in people.
Our takeOne letter separates the two abbreviations and roughly forty years of unrelated parent biology separates the molecules. The registry returns nothing for one of them and ten records for the other that turn out to be measuring rather than administering, which means the marketed uses of both rest on rodent work.
Frequently asked questions
Are semax and selank the same peptide?
No. Both are seven amino acids long and both carry a proline-glycine-proline tail, but semax is built from ACTH(4-10), a fragment of adrenocorticotropic hormone, and selank is built from tuftsin, a fragment released from the heavy chain of immunoglobulin G. Different parents, different systems, and evidence about one is not evidence about the other.
What do NASA and NAS stand for?
NASA is N-acetyl semax amidate and NAS is N-acetyl selank amidate. Those are the acetylated, amidated forms of the two peptides, and the two abbreviations differ by one letter. Listings swap them, which is the single most common mix-up in this group and the reason this page exists.
How many registered trials does each one have?
On 2 August 2026 a ClinicalTrials.gov search returned no study of semax under its own name, under N-acetyl semax, or under Semax ACTH. Selank returned 10, and reading them shows they are largely non-interventional or Russian-sponsored, with none testing the anxiety use the peptide is marketed for [7]. A registration count is not a count of completed trials, and in this category the two numbers are rarely the same.
Is either one approved in the United States?
No. A query of FDA's approved-products data on 2 August 2026 returned no application for either substance [10]. Both are registered medicines in Russia, which is a different regulatory system with different requirements, and a registration there carries no US status.
What did FDA's compounding committee do with semax in July 2026?
Semax-related bulk drug substances went before the Pharmacy Compounding Advisory Committee on 24 July 2026, as two separate voting questions covering the free base and the acetate. The meeting was noticed in the Federal Register on 16 April 2026 under docket FDA-2025-N-6895 [8], and the agency's voting-questions document names all seven substances put to the committee [9]. Selank was not among them. A committee recommendation is advisory in either direction, and FDA has published no vote record. Reporting says the committee recommended semax for inclusion, against FDA staff's own written proposal, and the 503A record on this site sets out what that did and did not change.
Does coming off FDA's Category 2 list mean a substance was added to the 503A Bulks List?
No, and the two are separate steps in the same process. FDA's interim categories sort nominated bulk drug substances while it evaluates them, and Category 2 flags substances raising significant safety risks. The Bulks List itself is the outcome of the evaluation, and a substance is added to it by rulemaking after the advisory committee process the Federal Register notice describes [8]. Moving off an interim category moves a substance from explicitly flagged to unlisted, which is not the same as being listed.
References
- Gusev EI, Skvortsova VI, Miasoedov NF, Nezavibat'ko VN, Zhuravleva EIu, Vanichkin AV. [Effectiveness of semax in acute period of hemispheric ischemic stroke (a clinical and electrophysiological study)]. Zh Nevrol Psikhiatr Im S S Korsakova. 1997. PMID 11517472
- Gusev EI, Martynov MY, Kostenko EV, Petrova LV, Bobyreva SN. [The efficacy of semax in the tretament of patients at different stages of ischemic stroke]. Zh Nevrol Psikhiatr Im S S Korsakova. 2018. PMID 29798983 DOI 10.17116/jnevro20181183261-68
- Dolotov OV, Karpenko EA, Inozemtseva LS, Seredenina TS, Levitskaya NG, Rozyczka J, Dubynina EV, Novosadova EV, Andreeva LA, Alfeeva LY, Kamensky AA, Grivennikov IA, Myasoedov NF, Engele J. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. 2006. PMID 16996037 DOI 10.1016/j.brainres.2006.07.108
- Czabak-Garbacz R, Cygan B, Wolański L, Kozlovsky I. Influence of long-term treatment with tuftsin analogue TP-7 on the anxiety-phobic states and body weight. Pharmacol Rep. 2006. PMID 16963804
- Kozlovskaya MM, Kozlovskii II, Val'dman EA, Seredenin SB. Selank and short peptides of the tuftsin family in the regulation of adaptive behavior in stress. Neurosci Behav Physiol. 2003. PMID 14969422 DOI 10.1023/a:1025988519919
- Kolik LG, Nadorova AV, Antipova TA, Kruglov SV, Kudrin VS, Durnev AD. Selank, Peptide Analogue of Tuftsin, Protects Against Ethanol-Induced Memory Impairment by Regulating of BDNF Content in the Hippocampus and Prefrontal Cortex in Rats. Bull Exp Biol Med. 2019. PMID 31625062 DOI 10.1007/s10517-019-04588-9
- US National Library of Medicine, ClinicalTrials.gov. Registry counts run through API v2 on 2 August 2026. Semax returned 0 studies, N-acetyl semax 0 and Semax ACTH 0. Selank returned 10, which on reading are largely non-interventional or Russian-sponsored and none of which tests the marketed anxiety use. ClinicalTrials.gov. 2026. Registry search
- US Food and Drug Administration. Pharmacy Compounding Advisory Committee; notice of meeting; establishment of a public docket; request for comments: bulk drug substances nominated for inclusion on the section 503A bulk drug substances list. Published 16 April 2026, document 2026-07361, Docket No. FDA-2025-N-6895. Federal Register, volume 91, page 20465. 2026. Meeting notice
- US Food and Drug Administration. Questions for PCAC regarding whether FDA should include certain bulk drug substances on the 503A Bulks List, Pharmacy Compounding Advisory Committee, 23 and 24 July 2026. The document names all seven substances put to a vote: BPC-157, KPV, TB-500, MOTS-c, emideltide, epitalon and semax. FDA advisory committee materials. 2026. Voting questions
- US Food and Drug Administration. Drugs@FDA approved products data, queried through the openFDA drug/drugsfda endpoint on 2 August 2026 for semax and for selank as active ingredients. No approved application was returned for either. openFDA. 2026. Query endpoint