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Semax vs Selank comes down to parent molecule and research focus. Both are synthetic seven-amino-acid peptides developed in Russia, and both end in the same Pro-Gly-Pro tail, but Semax is built on a fragment of the hormone ACTH1 while Selank is built on the immune peptide tuftsin2. In Russia, Selank is approved for anxiety and Semax has been used for neurological conditions including ischaemic stroke3; neither is an FDA-approved drug4, neither is authorised through the EU's centralised procedure5, and neither is named in Australia's Poisons Standard6.
Because the two are so often mentioned in the same breath, it is easy to assume they are variations on one compound. They are not. This comparison sets out how they differ in structure, in the models they have been studied in, in the mechanisms proposed for them and in the quality of the evidence behind each.
Chemical identifiers are as listed by PubChem.7,8 The other rows summarise the studies discussed below.
| Semax | Selank | |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP) | Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP) |
| Parent molecule | ACTH(4-7), a fragment of adrenocorticotropic hormone | Tuftsin (Thr-Lys-Pro-Arg), a fragment of the immunoglobulin G heavy chain |
| Molecular formula | C37H51N9O10S | C33H57N11O9 |
| Molar mass | 813.9 g/mol | 751.9 g/mol |
| CAS number | 80714-61-0 | 129954-34-3 |
| PubChem CID | 9811102 | 11765600 |
| Main research models | Experimental stroke in rats; learning tasks; neurotrophin signalling | Rodent anxiety and stress models; GABAergic gene expression |
| Leading proposed mechanism | Raised BDNF and trkB activation | Allosteric modulation of GABA-A binding; inhibition of enkephalin breakdown |
| Human evidence | Small Russian-language stroke studies | Small Russian-language anxiety trials against benzodiazepines |
| Status in Russia | On the list of vital and essential medicines | Approved for anxiety |
| FDA compounding page | Withdrawn category 2 nomination; potential immunogenicity risk noted9 | Withdrawn category 2 nomination; potential immunogenicity risk noted |
The same stabilising tail. Both peptides were built by attaching the tripeptide Pro-Gly-Pro, a "glyproline", to a short natural peptide. In Semax the tail increases resistance to peptidases1; in Selank it was added to improve metabolic stability and prolong action.2 The tail is the design feature intended to help both short peptides survive enzymatic breakdown for longer.
The same scientific home. Selank was designed at the Institute of Molecular Genetics of the Russian Academy of Sciences with the Zakusov Research Institute of Pharmacology2, and much of the Semax literature comes from the same institute and its collaborators.10 That shared origin is why the two are paired, and it is also a shared weakness: independent replication outside this network is limited for both.
Medicine status in Russia only. Semax is on Russia's list of vital and essential medicines1 and Selank is described as approved there for anxiety.3 Outside Russia, both are research compounds.
Semax takes positions 4 to 7 of ACTH (Met-Glu-His-Phe). ACTH is a pituitary hormone, but Semax is reported to have no hormonal activity.1 Selank takes tuftsin, a four-residue fragment of the heavy chain of human immunoglobulin G with immunomodulatory properties.2,3 The two parent peptides share no sequence, so any overlap in reported effects cannot be put down to a common active motif other than the tail.
Semax research concentrates on the brain's response to injury and on learning. A representative 2006 rat study reported that a single application of Semax raised hippocampal BDNF protein about 1.4-fold and increased activation of its receptor, trkB, alongside more conditioned avoidance responses.10 Much of the rest of the Semax literature measures gene expression after experimental stroke.
Selank research concentrates on anxiety-like behaviour. A 2018 radioligand study reported that Selank altered GABA binding in brain membrane preparations in a way consistent with positive allosteric modulation of GABA-A receptors, the site where benzodiazepines act.11 A 2016 rat study reported expression changes in 45 of 84 neurotransmission-related genes in the frontal cortex one hour after Selank, changes that correlated with those produced by GABA itself.2
The models differ as much as the molecules. Semax stroke studies typically use middle cerebral artery occlusion in rats, in which one of the brain's main arteries is blocked permanently or for a set time, then measure infarct size, behaviour or gene expression at fixed intervals. Selank studies lean on behavioural paradigms such as the elevated plus maze, which scores how much time a rodent spends in the open arms of a raised platform, often after weeks of unpredictable mild stress. Results from one family of models say little about the other, which is one reason the two literatures rarely meet.
In other words, Semax is studied mainly as a neurotrophic and neuroprotective candidate and Selank mainly as an anxiolytic candidate. Both descriptions come from preclinical work.
Head-to-head data are scarce. Two studies stand out.
What is missing is the obvious experiment: both peptides tested in the same animal model, at matched molar amounts, alongside a Pro-Gly-Pro-only control, with blinded scoring. None of the studies reviewed here used that design, so claims that one peptide outperforms the other in any model rest on comparisons across different papers, laboratories and methods.
For both peptides the clinical literature is small and published mostly in Russian.
Semax has been studied in people after ischaemic stroke. In a 2018 study, 110 patients in early or late rehabilitation were subdivided by whether they received Semax; the authors reported higher plasma BDNF and better Barthel index recovery in the Semax subgroups. The abstract does not describe randomisation, blinding or a placebo.14
Selank has been studied in anxiety-related disorders, with benzodiazepines as comparators. In a 2008 study, 62 patients with generalised anxiety disorder or neurasthenia received Selank or medazepam, and the authors reported similar anxiolytic effects in both groups.15 Clinical studies have been described as showing a spectrum of effects similar to benzodiazepines such as diazepam and phenazepam.2
Neither peptide has a trial registered on ClinicalTrials.gov (searched September 2026), and neither has been tested in the kind of large, independent, placebo-controlled trial that would support firm conclusions. That is why the popular question "which is better?" has no evidence-based answer.
For laboratory researchers the choice follows the question being asked. Work on ischaemia models, neurotrophin signalling or learning tasks has more Semax precedent to build on. Work on anxiety-like behaviour, GABAergic transmission, enkephalin metabolism or immune gene expression has more Selank precedent. Because both carry the same Pro-Gly-Pro tail, comparative designs benefit from controls that separate the effect of the tail from the effect of the parent sequence.
One practical point for comparative work: equal masses are not equal amounts. Using the PubChem molar masses, 1 mg of Semax free peptide is about 1.229 µmol, while 1 mg of Selank is about 1.330 µmol, roughly 8% more molecules. Salt forms such as acetates, and residual water, shift the real figures further, so equimolar designs should be calculated from each lot's stated net peptide content rather than from the label mass.7,8
Chemical stability also differs. Semax contains methionine, an amino acid whose sulphur-containing side chain is prone to oxidation; Selank's sequence has no methionine, cysteine or tryptophan. That can matter for storage and for solution stability over long experiments; see how to store peptides.
Both are supplied as lyophilised powders; the basics of synthesis, freeze-drying and research-use labelling are covered in our primer on what research peptides are. Titan Peptides supplies Semax 10 mg and Selank 10 mg for laboratory research only. For the full evidence on each, see the Semax research overview and the Selank research overview.
They are built on different natural peptides. Semax adds a Pro-Gly-Pro tail to ACTH(4-7), a fragment of the hormone ACTH, while Selank adds the same tail to tuftsin, a fragment of immunoglobulin G. Semax research focuses on experimental stroke and BDNF signalling; Selank research focuses on rodent anxiety models and GABA-A receptor binding.
There is no evidence-based answer. The two have never been compared in a large controlled trial, and their human studies are small, Russian-language and not placebo-controlled. They have mostly been studied in different models, so the useful question for researchers is which compound has more precedent for the model and endpoint being investigated.
Rarely. A 2001 in vitro study found that both inhibited enkephalin-degrading enzymes in human serum, with IC50 values of 10 µM for Semax and 20 µM for Selank. A 2020 imaging study in 52 healthy volunteers reported shared and distinct changes in amygdala connectivity after each peptide compared with placebo.
In Russia, Semax is on the list of vital and essential medicines and Selank is described as approved for anxiety. Neither is FDA-approved, neither is authorised through the EU centralised procedure, and neither is named in Australia's June 2026 Poisons Standard. Research-grade material is supplied for laboratory research only.
Pro-Gly-Pro is a glyproline tripeptide that the developers attached to both parent peptides to improve metabolic stability. According to papers from the developing institute, the tail increases resistance to peptidases, the enzymes that cut peptides apart, and lengthens duration of action. It is the main structural feature the two peptides share.
Semax is a seven-amino-acid ACTH fragment analogue listed as an essential medicine in Russia but not approved in the US or EU. Here is what the rodent and small clinical studies report, and how much weight they can bear.
Selank is a seven-amino-acid analogue of the immune peptide tuftsin, approved in Russia as an anti-anxiety medicine but not in the US or EU. This is what the published studies report, and how far they go.
A plain-English primer on research peptides: what a peptide is, how peptides are built one amino acid at a time on a resin bead, why they arrive as a freeze-dried powder, and what "research use only" does and does not mean.
