Semax vs Selank: Full Research Comparison of the Two Russian Nootropic Peptides

Semax is Met-Glu-His-Phe-Pro-Gly-Pro, C37H51N9O10S, molecular weight 813.9 g/mol, PubChem CID 9811102. The first four residues match positions 4 to 7 of ACTH, which is why the literature calls it an ACTH(4-10) analogue. The sequence is ACTH(4-7) extended with a Pro-Gly-Pro tail, so the label describes the family rather than the structure, and the tail is why a peptide that would otherwise be destroyed in minutes is measurable in brain tissue.

Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, C33H57N11O9, molecular weight 751.9 g/mol, PubChem CID 11765600. Tuftsin is the tetrapeptide Thr-Lys-Pro-Arg, a fragment of the immunoglobulin G heavy chain, and Selank is that tetrapeptide with the same three residue extension. The pharmacology literature calls it TP-7. It carries more positive charge than Semax, which changes how much of a compound crosses a membrane.

Both were developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, which explains the shared logic: a short active core plus three residues for metabolic stability. The label trap: N-acetyl Semax amidate, N-acetyl Selank amidate and comparable terminally protected variants are different molecules with different half-lives. A 99 percent purity certificate does not say which variant is in the vial.

Semax has the cleaner pharmacodynamic dataset. Dolotov and colleagues reported in the Journal of Neurochemistry that tritium-labelled Semax binds specifically, reversibly and calcium-dependently to membranes from the rat basal forebrain, with a dissociation constant of 2.4 nanomolar, and that intranasal doses of 50 and 250 micrograms per kilogram raised BDNF protein in the same region within three hours but not in the cerebellum. A companion paper in Brain Research found a 1.4-fold rise in hippocampal BDNF protein, a 1.6-fold rise in trkB phosphorylation and a 3-fold rise in BDNF exon III mRNA after a single 50 microgram per kilogram dose. Region specificity and a measurable binding site lift this above vendor copy, though the work comes from the developers' own institute.

Selank's mechanism is assembled from weaker threads: modulation of GABA-A signalling, enkephalinase inhibition, BDNF elevation in hippocampus and prefrontal cortex, and cytokine regulation including IL-6. The GABA claim is the weakest of them, which the next section covers.

The one mechanism both compounds share is documented. Kost and colleagues published in Bioorganic Chemistry that both heptapeptides inhibit enkephalin-degrading enzymes in human serum dose-dependently: Semax at an IC50 of 10 micromolar, Selank at 20 micromolar, both far more potent than puromycin at 10 millimolar. Pentapeptide fragments kept the effect, tri-, tetra- and hexapeptide fragments did not. A 2006 follow-up with tritium-labelled peptides mapped the breakdown products, so the degradation profile of both compounds is documented and any claim about in-solution stability has a specific answer sheet. What a micromolar IC50 does not describe is a plasma concentration after intranasal dosing, and that gap is where most of the marketing lives.

Selank is routinely described as a positive allosteric modulator of GABA-A receptors that enhances endogenous GABA tone without sedation. Follow the chain back and it does not start with receptor binding data. It starts with the clinical observation that Selank produces anxiolysis comparable to a benzodiazepine, plus the inference that similar effects imply a shared mechanism.

The study that tested the inference did not confirm it. Filatova and colleagues published in Frontiers in Pharmacology a qPCR panel of 84 genes involved in GABAergic neurotransmission in IMR-32 neuroblastoma cells. Selank alone changed the expression of none of them. Combined with GABA it almost completely suppressed the expression changes GABA alone produced. The authors concluded that the peptide has no direct effect on GABAergic gene expression and that their data only partially support an effect on the interaction of GABA with the GABA-A receptor. Interfering with a GABA response is not the same as potentiating it.

The review literature carries the same uncertainty. Doyno and White, in the Journal of Clinical Pharmacology, group Selank with phenibut as a poorly studied Russian drug with a GABAergic mechanism that is inexplicably sold to US consumers as a dietary supplement. Vyunova and colleagues treat the mechanism in a 2018 review as an open question.

Selank's human data sit in anxiety disorders. Zozulia and colleagues studied 62 patients with generalised anxiety disorder and neurasthenia: 30 received Selank, 32 received the benzodiazepine medazepam. Anxiolytic effects were similar, and Selank added antiasthenic and psychostimulant effects. The same study measured leu-enkephalin half-life in serum, reduced at baseline and correlated with symptom severity, and rising under Selank mainly in the generalised anxiety subgroup. Medvedev and colleagues compared Selank with phenazepam in 60 patients with phobic-anxiety and somatoform disorders and reported pronounced anxiolytic and mild nootropic effects, with anxiolysis persisting a week after the last dose.

Semax's human data sit in ischaemic stroke. Gusev and colleagues studied 30 patients in the acute period of hemispheric stroke against 80 conventionally treated patients, with EEG mapping and somatosensory evoked potentials as objective measures. The reported effective daily doses were 12 mg for moderate and 18 mg for severe strokes over 5 and 10 day courses. A 2018 study from the same group followed 110 patients using 6000 micrograms per day in two 10 day courses separated by 20 days. Plasma BDNF rose and stayed elevated, and Barthel index improvement was faster, with the largest effect alongside early rehabilitation.

Now the number that reframes the rest. Those protocols used 6 to 18 mg per day. Protocols circulating online use 200 to 400 micrograms, once or twice daily. That is a 15 to 90 fold difference, and route does not explain it: the trials used registered nasal formulations while vendors sell lyophilised powder for the same route or for subcutaneous use. Either the online protocols sit far below the exposure range in which the reported effects were observed, or the effects depend on a formulation a reconstituted powder does not reproduce. Both readings argue against citing the stroke trials as support for a powder protocol.

The human dataset also contains no placebo-controlled blinded trial in an English-language journal, no pharmacokinetic data at research doses, and no head-to-head study of the two peptides. The 1997 stroke work used a conventionally treated comparison group rather than random allocation, and the 2018 study compares treatment subgroups. The trials are real, the design is weaker than the citation style suggests, and the language of publication is why most of them never entered Western databases.

Neither compound is approved by the FDA or the EMA. Both are registered medicines in Russia, sold there as prescription nasal drops, Semax at 0.1 percent and Selank at 0.15 percent. Everything outside that market is a research chemical, and that market is where identity problems concentrate.

Vanhee and colleagues at Sciensano in Belgium described two seized preparations that contained Selank and Semax, noted that the peptides had, to their knowledge, not completed any clinical trials, and built an LC-MS/MS method covering ten nootropic peptides in response. That statement says little about the actual trial history, which exists but is published almost entirely in Russian, and a lot about how invisible that literature is to Western regulators and customs laboratories. A European buyer therefore receives material with no regulatory assessment attached at all.

• Purity is not identity. A 99 percent pure sample of the wrong peptide is still the wrong peptide. The amidated and acetylated variants differ from the parent by small mass shifts, so the certificate has to state the sequence and the observed mass.
• Batch linkage. The report must name the batch printed on the vial. A generic certificate with a vendor logo and no batch number cannot be tied to the material in front of you.

For sport the picture is simpler: any substance without approval from a national regulatory authority falls under the S0 catch-all of the prohibited list, which is why both appear in doping control method development rather than in approved literature.

The registered Russian formulations are far more concentrated than working solutions in research protocols, and both compounds are discussed in micrograms while arriving as milligram vials. That mismatch is the most common arithmetic error in a two peptide protocol.