Selank vs Semax
Selank and Semax are synthetic heptapeptides developed in Russia, each ending in a Pro-Gly-Pro extension. Selank is a tuftsin analogue studied for anxiety-related effects; Semax is an ACTH(4-10) analogue studied in neurological settings.
Selank and Semax were both developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, and both use the same design idea: a short fragment of a natural regulatory peptide extended with a C-terminal Pro-Gly-Pro sequence to slow enzymatic breakdown.
Their parent peptides differ. Selank is built on tuftsin, an immunomodulatory tetrapeptide, and has been studied mainly for anxiety-related and immune effects. Semax is built on a fragment of adrenocorticotropic hormone (ACTH) without its hormonal activity, and has been studied for neuroprotective and cognitive effects. Most of the published literature for both comes from Russian research groups, and independent replication is limited.
Side-by-side
| Attribute | Selank | Semax |
|---|---|---|
| Parent peptide | Tuftsin (Thr-Lys-Pro-Arg) | ACTH(4-7) fragment of adrenocorticotropic hormone |
| Sequence | Thr-Lys-Pro-Arg-Pro-Gly-Pro | Met-Glu-His-Phe-Pro-Gly-Pro |
| Length | 7 residues | 7 residues |
| Design feature | C-terminal Pro-Gly-Pro added for stability | C-terminal Pro-Gly-Pro added for stability; lacks corticotropic activity |
| Proposed mechanisms | Modulation of GABAergic and monoamine signaling and of immune cytokines (proposed) | Increased BDNF expression and effects on monoamine systems (proposed) |
| Research areas | Animal models of anxiety and stress; small clinical studies in Russia | Animal models of cerebral ischemia and cognition; clinical studies in Russia |
| Evidence level | Early-clinical; mostly single-country literature | Early-clinical; mostly single-country literature |
| Regulatory status | Not approved by the FDA; registered in Russia | Not approved by the FDA; registered in Russia; PCAC voted in July 2026 to recommend 503A bulk listing, no final FDA action |
| Analytical pitfalls | Basic residues (Lys, Arg) carry counter-ions; check salt form | N-terminal Met is prone to oxidation (+16 Da species); check for sulfoxide impurity |
Shared design, different parent peptides
Both peptides illustrate a strategy used in Russian peptide pharmacology: take a short active fragment of an endogenous peptide and attach Pro-Gly-Pro, a sequence that resists many peptidases. Tuftsin, the basis of Selank, is a fragment of the immunoglobulin G heavy chain associated with phagocyte activation. The ACTH(4-7) fragment at the start of Semax was chosen because ACTH fragments of this region show central nervous system activity in animals without stimulating the adrenal cortex.
Research focus and evidence
Selank has been studied mainly in rodent models of anxiety and stress, with some small clinical studies reported from Russia. Semax has been studied in animal models of stroke and cognitive impairment and in Russian clinical settings. In both cases most publications come from a few closely linked institutions, many in Russian-language journals. Independent controlled trials outside Russia are largely absent, so the evidence is best described as early-clinical and regionally concentrated.
Analytical and stability differences
Semax begins with methionine, which oxidizes easily to methionine sulfoxide. This shows up as a +16 Da species by mass spectrometry and often as a separate HPLC peak, so exposure to air and light matters during storage. Selank contains no methionine, tryptophan or cysteine, but its lysine and arginine residues carry counter-ions, so net peptide content depends on the salt form. Both are usually handled lyophilized at -20 °C, protected from light and moisture. See counter-ions: TFA vs acetate.
Frequently asked questions
What is the difference between Selank and Semax?
Both are seven-residue synthetic peptides ending in Pro-Gly-Pro, developed at the same Russian institute. Selank is derived from tuftsin and has been studied mainly in anxiety and stress models. Semax is derived from an ACTH fragment and has been studied mainly in models of cerebral ischemia and cognition. Their sequences and proposed mechanisms differ.
Are Selank and Semax FDA approved?
Neither is approved by the FDA for any use. Both are registered as medicines in Russia. In July 2026 the FDA's Pharmacy Compounding Advisory Committee voted to recommend adding Semax to the 503A bulk drug substances list; that vote is advisory, and no final FDA action has been announced.
Is Semax a hormone?
Semax is derived from a fragment of adrenocorticotropic hormone, but the fragment was chosen because it lacks ACTH's ability to stimulate cortisol release from the adrenal cortex. It is therefore classed as a regulatory peptide analogue rather than a corticotropic hormone.
Full entries
- Selank
Selank is a synthetic heptapeptide developed in Russia, built from the immunomodulatory tetrapeptide tuftsin extended with a Pro-Gly-Pro tail. It is studied mainly for effects on anxiety-related behavior and immune signaling.
- Semax
Semax is a synthetic heptapeptide developed in Russia as an analogue of the adrenocorticotropic hormone fragment ACTH(4-7), extended with a Pro-Gly-Pro tail. It is studied for neurotrophic signaling and in models of brain injury.
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