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Residue An evidence-graded reference for peptide science

Selank vs semax

C Selank Proposed: allosteric GABA-A modulation and enkephalinase inhibition Not FDA-approved · FDA compounding nomination withdrawn C Semax ACTH(4-7) analog; proposed neuroimmune and neurotrophic (BDNF) effects Not FDA-approved · FDA compounding nomination withdrawn

Residue Editorial Team · updated

In brief

Selank and semax are synthetic heptapeptides studied mainly in Russia. Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) was studied for anxiety: in 62 patients its effect was similar to the benzodiazepine medazepam1PubMed[Efficacy and possible mechanisms of action of a new peptide anxiolytic selank in the therapy of generalized anxiety disorders and neurasthenia]. Zozulia AA et al. Zh Nevrol Psikhiatr Im S S Korsakova. 2008.. Semax (ACTH(4-7) plus Pro-Gly-Pro) was studied in ischemic stroke, with reports of better recovery and higher BDNF2PubMed[The efficacy of semax in the tretament of patients at different stages of ischemic stroke]. Gusev EI et al. Zh Nevrol Psikhiatr Im S S Korsakova. 2018.. Neither has large randomized trials or FDA approval3FDACertain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. U.S. FDA, content current as of 04/22/2026..

How do Selank and Semax compare at a glance?

Table 1. Selank and Semax on the dimensions that matter most; every entry is cited.
DimensionSelankSemax
SequenceThr-Lys-Pro-Arg-Pro-Gly-Pro4PubMedThe inhibitory effect of Selank on enkephalin-degrading enzymes as a possible mechanism of its anxiolytic activity. Zozulya AA et al. Bull Exp Biol Med. 2001.Met-Glu-His-Phe-Pro-Gly-Pro5PubMedSemax, an analog of ACTH((4-7)), regulates expression of immune response genes during ischemic brain injury in rats. Medvedeva EV et al. Mol Genet Genomics. 2017.
Studied forAnxiety, neurasthenia1Ischemic stroke2,6PubMed[Effectiveness of semax in acute period of hemispheric ischemic stroke (a clinical and electrophysiological study)]. Gusev EI et al. Zh Nevrol Psikhiatr Im S S Korsakova. 1997.
Largest clinical study62 patients vs medazepam1110 stroke patients, 5 months2
Proposed mechanismGABA allosteric modulation; enkephalinase inhibition7PubMedPeptide-based Anxiolytics: The Molecular Aspects of Heptapeptide Selank Biological Activity. Vyunova TV et al. Protein Pept Lett. 2018.,4BDNF; immune and vascular gene expression after ischemia2,8PubMedThe peptide semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia: genome-wide transcriptional analysis. Medvedeva EV et al. BMC Genomics. 2014.
Registered trialsNone; the 2 search hits are unrelated device studies9TrialClinicalTrials.gov registry search: selank. 2 registered studies at fetch.None on ClinicalTrials.gov at fetch10TrialClinicalTrials.gov registry search: semax. 0 registered studies at fetch.
FDAWithdrawn nomination3Withdrawn nomination3
Evidence gradeCC

Written by Residue Editorial Team

Reviewed by Residue Editorial Team · source-by-source check,

First published

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Registry data · How we grade · Markdown + sources

Figure 1. Size of the research record, from PubMed and ClinicalTrials.gov at the data edition. Bars are scaled to the larger value in each row; volume is not quality.
PubMed records 68 209
Trial publications 3 4
Registered studies 2 0
Phase 3 studies 0 0

Selank Semax

Both peptides end in the tripeptide Pro-Gly-Pro. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro4. Semax joins the ACTH(4-7) fragment to Pro-Gly-Pro, giving Met-Glu-His-Phe-Pro-Gly-Pro5,11PubChemPubChem compound record: ACTH (4-7), Pro-Gly-Pro-. C37H51N9O10S · MW 813.9 g/mol..

What is the evidence for Selank?

In 62 patients with generalized anxiety disorder or neurasthenia, selank (30 patients) and medazepam (32) had similar anxiolytic effects, and selank also showed anti-asthenic and psychostimulant effects1. Laboratory work found it inhibited enzymatic breakdown of plasma enkephalin (IC50 15 µM)4, acted as a positive allosteric modulator of GABA binding7, and in rat frontal cortex changed expression of 45 of 84 neurotransmission genes within an hour12PubMedSelank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission. Volkova A et al. Front Pharmacol. 2016..

What is the evidence for Semax?

In 110 ischemic-stroke patients followed for five months, semax raised plasma BDNF and was associated with better Barthel index outcomes, particularly alongside early rehabilitation2. A 1997 study added semax to therapy in 30 acute stroke patients and compared them with 80 conventionally treated controls, reporting faster neurological recovery6. In rats after focal brain ischemia, semax mainly altered immune-response genes plus 24 vascular genes at 3 hours8.

How should this evidence be read?

Neither record includes a large, placebo-controlled, multicenter trial, and ClinicalTrials.gov held no registered trial testing either peptide at our fetch9,10. That is why both sit at Grade C on our evidence scale.

Are they FDA-approved?

FDA lists selank acetate and semax among withdrawn compounding nominations and says it lacks important safety information for humans3. Neither is FDA-approved.

Two identical glass beakers, one holding pale amber liquid and one clear, standing either side of a brass balance

Why do they get these evidence grades?

C Selank
Small clinical studies in Russian journals, including a 62-patient comparison with medazepam; no large randomized placebo-controlled trial indexed in PubMed. Grade C: Limited / early human data.
C Semax
Small clinical studies in stroke published in Russian journals, without large randomized controlled trials; mechanism work is in rats. Grade C: Limited / early human data.

Questions readers ask

What is the difference between selank and semax?

They share a Pro-Gly-Pro tail but differ otherwise: selank's other residues are Thr-Lys-Pro-Arg4, while semax builds on the ACTH(4-7) fragment5. Selank was studied for anxiety1, semax for stroke2.

Are selank and semax FDA-approved?

No. FDA lists both among withdrawn compounding nominations and states it lacks safety information about them3.

How strong is the clinical evidence?

Limited. The studies are small and published in Russian journals; the 1997 semax stroke study compared 30 treated patients with 80 conventionally treated controls6, and the selank study compared two active treatments without placebo1.

Can you take selank and semax together?

No published trial among the sources we cite tested them together. Both remain unapproved in the US, and FDA lists them among withdrawn compounding nominations3.

References

Every source below was retrieved from its official API or page and cached on the data-edition date. Numbers match the margin notes.

  1. 1 PubMed 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. PMID 18454096.
  2. 2 PubMed Gusev EI, Martynov MY, Kostenko EV, et al. [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.
  3. 3 FDA Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. U.S. FDA, content current as of 04/22/2026.
  4. 4 PubMed Zozulya AA, Kost NV, Yu Sokolov O, et al. The inhibitory effect of Selank on enkephalin-degrading enzymes as a possible mechanism of its anxiolytic activity. Bull Exp Biol Med 2001. PMID 11550013; doi:10.1023/a:1017979514274.
  5. 5 PubMed Medvedeva EV, Dmitrieva VG, Limborska SA, et al. Semax, an analog of ACTH((4-7)), regulates expression of immune response genes during ischemic brain injury in rats. Mol Genet Genomics 2017. PMID 28255762; doi:10.1007/s00438-017-1297-1.
  6. 6 PubMed Gusev EI, Skvortsova VI, Miasoedov NF, et al. [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.
  7. 7 PubMed Vyunova TV, Andreeva L, Shevchenko K, et al. Peptide-based Anxiolytics: The Molecular Aspects of Heptapeptide Selank Biological Activity. Protein Pept Lett 2018. PMID 30255741; doi:10.2174/0929866525666180925144642.
  8. 8 PubMed Medvedeva EV, Dmitrieva VG, Povarova OV, 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. PMID 24661604; doi:10.1186/1471-2164-15-228.
  9. 9 ClinicalTrials.gov ClinicalTrials.gov registry search: selank. 2 registered studies at fetch.
  10. 10 ClinicalTrials.gov ClinicalTrials.gov registry search: semax. 0 registered studies at fetch.
  11. 11 PubChem PubChem compound record: ACTH (4-7), Pro-Gly-Pro-. C37H51N9O10S · MW 813.9 g/mol.
  12. 12 PubMed Volkova A, Shadrina M, Kolomin T, et al. Selank Administration Affects the Expression of Some Genes Involved in GABAergic Neurotransmission. Front Pharmacol 2016. PMID 26924987; doi:10.3389/fphar.2016.00031.