Selank and Semax: What's the Difference

TL;DR: The core difference is origin and the mechanism under study. Selank is derived from the immune peptide tuftsin, with research focused on GABAergic and immune modulation. Semax is an ACTH(4–10) fragment, studied in neurotrophic (BDNF/NGF) and neuroprotection models. Both are for laboratory research only.

Selank (CAS 129954-34-3) and Semax (CAS 80714-61-0) are two short peptides developed at the Institute of Molecular Genetics of the Russian Academy of Sciences. Both are listed in Russia's Vital and Essential Drugs registry and have an unusually long publication track for short peptides, with decades of Russian-language preclinical and clinical literature. Outside Russia, they are studied almost exclusively as research compounds.

What Is Selank?

Selank is a synthetic heptapeptide derived from a fragment of Tuftsin, a naturally occurring tetrapeptide produced in the spleen. The original Tuftsin sequence (Thr-Lys-Pro-Arg) is metabolised in plasma within minutes; Selank adds a Pro-Gly-Pro tail that confers protease resistance and extends activity into the hours range. Sequence: Thr-Lys-Pro-Arg-Pro-Gly-Pro.

Primary research interest in Selank centres on its GABAergic modulation. Published preclinical work shows Selank upregulates GABA receptor binding affinity in rat hippocampus and modulates serotonin and dopamine turnover indirectly. It has been studied as an anxiolytic and immunomodulatory candidate.

• CAS: 129954-34-3
• Sequence: Thr-Lys-Pro-Arg-Pro-Gly-Pro
• Molecular weight: 751.9 Da
• Half-life: Estimated 10 to 30 minutes intranasally, longer with depot formulations

What Is Semax?

Semax is a synthetic heptapeptide derived from ACTH 4-10, an internal fragment of adrenocorticotropic hormone with documented CNS activity but no corticotropic effect. Like Selank, the parent fragment is rapidly degraded; Semax adds Pro-Gly-Pro at the C-terminus for protease resistance. Sequence: Met-Glu-His-Phe-Pro-Gly-Pro.

Semax research focuses on neurotrophic and neuroprotective pathways. Documented effects in animal models include BDNF and NGF upregulation in hippocampal and cortical neurons, modulation of enkephalin metabolism, and antioxidant activity through nitric oxide pathway modulation.

• CAS: 80714-61-0
• Sequence: Met-Glu-His-Phe-Pro-Gly-Pro
• Molecular weight: 813.9 Da
• Half-life: Estimated 15 to 30 minutes intranasally

What's the difference between Selank and Semax?

Selank or Semax: which do researchers choose?

The choice follows the research model, not "potency." Selank appears more often in anxiety, behavioral, and immune-regulation models; Semax in memory, learning, neuroprotection, and ischemia models. Comparative protocols sometimes include both as separate arms. For in-vitro research only.

Why the Russian Research Track Matters

The publication base for both compounds is heavily weighted to Russian-language journals (Bulletin of Experimental Biology and Medicine, Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova, Eksperimental'naya i Klinicheskaya Farmakologiya). Researchers working from English-only databases will see only a fraction of the literature, and key dosing and pharmacokinetic data live in the Russian sources. Reading the original literature, or working with translations from primary Russian publications, is the difference between informed protocol design and guesswork.

Stack Considerations

Selank and Semax are mechanistically distinct and have been studied together in preclinical models of combined neuroprotective plus anxiolytic effect. They engage different receptor systems, which makes the combination additive rather than redundant. Some Russian publications discuss combined nasal protocols, though comparative head-to-head data remain limited outside that literature.

Purity and COA Requirements

Both peptides require ≥99% HPLC-MS verified purity. Common impurities include desulfated species (Semax in particular contains methionine, which is susceptible to oxidation) and truncated sequences from incomplete synthesis. A real Certificate of Analysis should include the HPLC chromatogram, mass spectrometry confirmation, and a methionine oxidation check for Semax specifically.

Summary

Selank and Semax are complementary research peptides with strong Russian-language publication histories. Selank operates primarily through GABAergic and immunomodulatory pathways. Semax acts through neurotrophic factor upregulation and neuroprotective mechanisms. Researchers comparing the two should engage with the primary Russian literature and prioritise HPLC-MS verified purity.