What Are Semax and Selank?
By the Zen Well Labs Research Team · Last reviewed September 2026 · For laboratory research reference only
Short answer: Semax and Selank are two different synthetic heptapeptides (seven amino acids each) developed at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow. Both end in the same Pro-Gly-Pro tripeptide, but their first four residues come from different natural peptides. Semax is Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP), built from the ACTH(4-7) fragment: formula C37H51N9O10S, molecular weight ≈813.9 Da, CAS 80714-61-0, PubChem CID 9811102. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP), built from the immunoglobulin-derived tetrapeptide tuftsin: formula C33H57N11O9, molecular weight ≈751.9 Da, CAS 129954-34-3, PubChem CID 11765600. Most of the published work comes from cell-culture and rodent models. Neither peptide is approved by the FDA for any use. Zen Well Labs sells both for in-vitro laboratory research only.
Semax and Selank at a glance
| Identifier | Semax | Selank |
|---|---|---|
| Type | Synthetic linear heptapeptide | Synthetic linear heptapeptide |
| Parent fragment | ACTH(4-7): Met-Glu-His-Phe | Tuftsin: Thr-Lys-Pro-Arg |
| C-terminal extension | Pro-Gly-Pro | Pro-Gly-Pro |
| Sequence (one-letter) | MEHFPGP | TKPRPGP |
| Sequence (three-letter) | H-Met-Glu-His-Phe-Pro-Gly-Pro-OH | H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH |
| Molecular formula | C37H51N9O10S | C33H57N11O9 |
| Molecular weight (average) | ≈813.9 Da | ≈751.9 Da |
| Monoisotopic mass | ≈813.348 Da | ≈751.434 Da |
| CAS number | 80714-61-0 | 129954-34-3 |
| PubChem CID | 9811102 | 11765600 |
| FDA UNII | I5FAL2585H | TS9JR8EP1G |
| Contains sulfur (Met) | Yes | No |
| Typical supplied form | Lyophilized powder (Zen Well Labs: 5 mg vial) | Lyophilized powder (Zen Well Labs: 5 mg vial) |
| US regulatory status | Not FDA-approved for any use; research chemical | Not FDA-approved for any use; research chemical |
Two peptides, one design strategy
Semax and Selank are often discussed together because they share a laboratory of origin and a design idea. Short natural regulatory peptides tend to be broken down quickly by proteases. The Moscow group, associated with N. F. Myasoedov and I. P. Ashmarin, added a C-terminal Pro-Gly-Pro (PGP) tripeptide to short bioactive fragments to make them more resistant to enzymatic degradation. Kolomin and colleagues (Neuroscience & Medicine, 2013) review this programme and both peptides in detail.
What they share ends there. The N-terminal four residues, which carry most of each peptide’s reported activity, are different:
- Semax starts with Met-Glu-His-Phe, residues 4–7 of adrenocorticotropic hormone (ACTH).
- Selank starts with Thr-Lys-Pro-Arg, the tetrapeptide tuftsin, first described by Najjar and colleagues as a fragment of the immunoglobulin G heavy chain.
The two peptides differ by about 62 Da in average mass, have different elemental compositions (only Semax contains sulfur) and are not interchangeable reference materials. A mass-spectrometry result near 814 Da points to Semax. A result near 752 Da points to Selank.
Semax
Identity
PubChem lists Semax under CID 9811102 with the synonym H-Met-Glu-His-Phe-Pro-Gly-Pro-OH. Its record title is “ACTH (4-7), Pro-Gly-Pro-“, which states the design directly. Literature descriptions vary: many papers call Semax “an analog of ACTH(4-10)”, because Pro-Gly-Pro replaces the native residues 8–10 of that longer fragment. Others, including more recent work from the same institute, describe it as “ACTH(4-7)PGP”. Both descriptions refer to the same heptapeptide, MEHFPGP.
Because the N-terminal residue is methionine, Semax can oxidise to methionine sulfoxide (+16 Da). That is worth watching for in MS data from older or poorly stored material.
Catalogues also list modified variants, such as N-acetylated and/or C-terminally amidated “Semax” derivatives. These are different chemical entities with different masses and registry entries. The identifiers on this page apply only to the unmodified heptapeptide. Magrì and colleagues (Journal of Inorganic Biochemistry, 2016), for example, reported that N-terminal acetylation changes Semax’s copper(II) and zinc(II) coordination behaviour, which is a reminder that small modifications change the chemistry.
What has the published research looked at?
The Semax literature is concentrated in Russian research groups. Recurring preclinical themes include:
- Neurotrophin expression in rodent brain. Dolotov and colleagues (Brain Research, 2006) reported increased BDNF protein and trkB phosphorylation, along with raised BDNF and trkB mRNA, in the rat hippocampus after Semax administration. A companion paper (Journal of Neurochemistry, 2006) reported specific binding in rat basal forebrain membranes.
- Rat cerebral ischemia models (gene expression). Published gene-expression studies used rat focal cerebral ischemia models (Dmitrieva et al., 2010; Medvedeva et al., 2014, 2017).
These are model-specific findings in animal tissue. They do not establish safety or efficacy in humans.
Selank
Identity
PubChem lists Selank under CID 11765600 (H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH; formula C33H57N11O9; ≈751.9 Da; CAS 129954-34-3). The first four residues are tuftsin (Thr-Lys-Pro-Arg), which Najjar and co-workers characterised in the early 1970s. Selank has two basic residues (Lys, Arg) and no methionine, so it is more basic than Semax and lacks Semax’s oxidation-prone thioether.
What has the published research looked at?
- GABAergic system readouts. Vyunova et al. (Protein & Peptide Letters, 2018) used radioligand binding on rat brain membrane preparations and reported that Selank changed [3H]GABA binding in a way consistent with allosteric modulation. In human neuroblastoma IMR-32 cells, Filatova et al. (Frontiers in Pharmacology, 2017) found no direct Selank effect on the mRNA levels of 84 GABAergic and neurotransmission genes, but did see changes when Selank was combined with GABA or olanzapine. This is a useful example of an in-vitro result that qualifies earlier hypotheses.
- Gene expression in rodent tissue. Volkova et al. (Frontiers in Pharmacology, 2016) measured expression of 84 neurotransmission-related genes in rat frontal cortex after Selank or GABA administration. Kolomin et al. (Molecular Immunology, 2014) followed the time course of inflammation-related gene expression (C3, Casp1, Il2rg, Xcr1) in mouse spleen after Selank or its Gly-Pro fragment was given.
As with Semax, these are cell-line and rodent-model findings, not evidence of human safety or efficacy.
Semax vs Selank: how to keep them straight
| Question | Semax | Selank |
|---|---|---|
| Which natural fragment? | ACTH(4-7) | Tuftsin (IgG-derived) |
| Main literature themes | Neurotrophin (BDNF/trkB) expression; gene expression in rat ischemia models | GABAergic readouts; immune/inflammation gene expression |
| Mass check | ≈813.9 Da | ≈751.9 Da |
| Oxidation-prone residue | Met1 | None |
For more on how short peptides are compared side by side, see our BPC-157 vs TB-500 comparison.
Regulatory status: United States and elsewhere
In the United States, neither Semax nor Selank is an FDA-approved drug, and neither is an approved food, cosmetic or dietary supplement. There is no FDA-approved product containing either peptide. Zen Well Labs lists both as research chemicals for in-vitro use only.
Their status outside the United States is different, and it should be stated accurately. Both peptides were developed as medicinal products in the Russian Federation. Kolomin et al. (2013) report that a Selank formulation was registered by the Russian Ministry of Health in 2009, and a Semax product appears in the Russian State Register of Medicinal Products (GRLS). We note this only as regulatory history. Registration in one country does not create approval, equivalence or any authorised use in the United States, and it has no bearing on how research-grade material from Zen Well Labs may be used. Most of the clinical literature on both peptides was published in Russian and has not been reviewed by the FDA.
What is missing
- Independent replication. Most studies come from a small group of closely connected Russian institutions. Independent, international replication is limited.
- Physico-chemical characterisation. Published stability, degradation-product and impurity-profile data for research-grade material are sparse compared with the bioassay literature.
- Western regulatory review. There are no FDA-reviewed randomized controlled trial data for either peptide. Claims that turn rodent or cell-culture observations into human benefits go beyond the evidence and the legal status of these materials.
Storage and stability in the laboratory
Store both peptides as sealed lyophilized powder: keep vials closed, dry and protected from light, at −20 °C for long-term storage. Short periods at 2–8 °C are generally tolerated for sealed dry material. Let a cold vial reach room temperature before opening so moisture does not condense on the powder, and reseal promptly. Semax needs extra care against oxidation because of its N-terminal methionine. Keep vials tightly sealed to limit air exposure, and re-check the mass if a +16 Da species appears on a later analysis. See our guide to lyophilized peptide storage and stability for general principles.
How are Semax and Selank identity and purity verified?
Reversed-phase HPLC reports purity as percent peak area. Mass spectrometry confirms which peptide is in the vial: ≈813.9 Da (average; monoisotopic ≈813.35) for Semax, and ≈751.9 Da (average; monoisotopic ≈751.43) for Selank. The two peptides differ by about 62 Da, so an MS result settles any labelling mix-up at once. A Certificate of Analysis should report both results and a batch number, and ideally the CAS number used. Our guide on how to read a peptide COA explains each field.
Frequently asked questions
Are Semax and Selank the same peptide?
No. Both are heptapeptides ending in Pro-Gly-Pro, but Semax (MEHFPGP) is built on ACTH(4-7) and Selank (TKPRPGP) is built on tuftsin. They have different formulas, masses and CAS numbers.
What is the sequence of Semax?
Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP). Formula C37H51N9O10S, ≈813.9 Da, CAS 80714-61-0, PubChem CID 9811102. Back to the Semax section.
What is the sequence of Selank?
Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP). Formula C33H57N11O9, ≈751.9 Da, CAS 129954-34-3, PubChem CID 11765600. Back to the Selank section.
Why is Semax called both an ACTH(4-7) and an ACTH(4-10) analog?
The first four residues match ACTH(4-7), and Pro-Gly-Pro takes the place of native residues 8–10. Papers use either description for the same molecule.
Are Semax and Selank FDA-approved?
No. Neither is approved by the FDA for any use. Their regulatory history in the Russian Federation does not change their US status.
Is N-acetyl Semax the same as Semax?
No. Acetylated and/or amidated derivatives are separate chemical entities with different masses. The identifiers on this page apply only to unmodified Semax.
What are Zen Well Labs Semax and Selank products intended for?
In-vitro laboratory research only. They are not for human or veterinary use.
References
- Kolomin T, Shadrina M, Slominsky P, Limborska S, Myasoedov N. A New Generation of Drugs: Synthetic Peptides Based on Natural Regulatory Peptides. Neuroscience & Medicine. 2013;4(4):223–252. doi:10.4236/nm.2013.44035.
- Dolotov OV, Karpenko EA, Inozemtseva LS, Seredenina TS, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Research. 2006;1117(1):54–60.
- Dolotov OV, Karpenko EA, Seredenina TS, Inozemtseva LS, et al. Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain. Journal of Neurochemistry. 2006;97(Suppl 1):82–86.
- Dmitrieva VG, Povarova OV, Skvortsova VI, Limborska SA, et al. Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia. Cellular and Molecular Neurobiology. 2010;30(1):71–79.
- Medvedeva EV, Dmitrieva VG, Povarova OV, Limborska SA, et al. The peptide semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia: genome-wide transcriptional analysis. BMC Genomics. 2014;15:228.
- Medvedeva EV, Dmitrieva VG, Limborska SA, Myasoedov NF, et al. Semax, an analog of ACTH(4-7), regulates expression of immune response genes during ischemic brain injury in rats. Molecular Genetics and Genomics. 2017;292(3):635–653.
- Magrì A, Tabbì G, Giuffrida A, Pappalardo G, et al. Influence of the N-terminus acetylation of Semax, a synthetic analog of ACTH(4-10), on copper(II) and zinc(II) coordination and biological properties. Journal of Inorganic Biochemistry. 2016;164:59–69.
- Vyunova TV, Andreeva L, Shevchenko K, Myasoedov N. Peptide-based anxiolytics: the molecular aspects of heptapeptide Selank biological activity. Protein & Peptide Letters. 2018;25(10):914–923.
- Filatova E, Kasian A, Kolomin T, Rybalkina E, et al. GABA, Selank, and olanzapine affect the expression of genes involved in GABAergic neurotransmission in IMR-32 cells. Frontiers in Pharmacology. 2017;8:89.
- Volkova A, Shadrina M, Kolomin T, Andreeva L, et al. Selank administration affects the expression of some genes involved in GABAergic neurotransmission. Frontiers in Pharmacology. 2016;7:31.
- Kolomin T, Morozova M, Volkova A, Shadrina M, et al. The temporary dynamics of inflammation-related genes expression under tuftsin analog Selank action. Molecular Immunology. 2014;58(1):50–55.
- Nishioka K, Sato PS, Constantopoulos A, Najjar VA. The chemical synthesis of the phagocytosis-stimulating tetrapeptide tuftsin (Thr-Lys-Pro-Arg) and its biological properties. Biochimica et Biophysica Acta. 1973;310(1):230–237.
- PubChem Compound Summary, CID 9811102 (Semax; ACTH (4-7), Pro-Gly-Pro-). National Center for Biotechnology Information.
- PubChem Compound Summary, CID 11765600 (Selank). National Center for Biotechnology Information.
Related
- What is Epithalon?
- BPC-157 vs TB-500
- How to read a peptide COA
- Lyophilized peptide storage and stability
Research use only. All products sold by Zen Well Labs are intended strictly for in-vitro laboratory research. They are not drugs, foods, cosmetics or dietary supplements, are not approved by the FDA for any use, and are not for human or veterinary use. Nothing on this page is medical advice, and nothing here describes or recommends administration to humans or animals.
