Selank vs Semax

How they're alike

Selank and Semax are sibling peptides — both are synthetic heptapeptides developed at the Institute of Molecular Genetics of the Russian Academy of Sciences using the same design strategy: attach a Pro-Gly-Pro (PGP) tail to a short biologically interesting fragment, gaining proteolytic stability and a functional duration that the parent fragment lacks. Selank fuses PGP to the tuftsin tetrapeptide Thr-Lys-Pro-Arg (Vyunova 2018), while Semax fuses PGP to the ACTH(4-7) fragment Met-Glu-His-Phe (Eremin 2005). A local alignment of the two seven-residue sequences (TKPRPGP vs MEHFPGP) shares exactly the three C-terminal PGP residues — the stability motif — and no others, so they are structural cousins rather than analogs. Both are administered intranasally, both upregulate brain-derived neurotrophic factor in rodent brain regions (Dolotov 2006 for Semax; Kolik 2019 for Selank), and both inhibit human-serum enkephalin-degrading enzymes — a property that was characterized side-by-side in a single 2001 study comparing the two compounds (Kost 2001). Both also have a notably similar regulatory posture: prescription approval in Russia (and selected CIS countries) but no FDA, EMA, MHRA, or Health Canada authorization.

How they differ

The parent fragments diverge sharply, and so does the lead pharmacology. Semax was engineered to keep the cognitive-enhancing properties of the ACTH(4-10) fragment while excising the steroidogenic ACTH(1-24) segment, so the molecule does not stimulate the adrenal axis (Eremin 2005). Its primary reported pathway is melanocortin-4 receptor agonism in the hippocampus and cortex, which drives BDNF mRNA upregulation within roughly 30 minutes of an intranasal dose and persists for around 24 hours in rodent models (Dolotov 2006; Shadrina 2010). Semax additionally modulates GABA- and glycine-activated ionic currents in isolated cerebral neurons (Sharonova 2018) and influences ischemia-related immune-response gene expression in rat brain (Medvedeva 2017).

Selank's pharmacology is anchored on a different scaffold. The dominant reported mechanism is allosteric enhancement of GABA-A receptor function — not benzodiazepine-site agonism — together with documented effects on GABAergic gene expression in IMR-32 neuronal cells (Volkova 2016; Filatova 2017). On top of that, Selank retains the immunomodulatory lineage of tuftsin: cytokine balance under stress (Leonidovna 2021), enkephalinase inhibition as a proposed contributor to its anxiolytic activity (Zozulya 2001), and a broader peptide-anxiolytic literature reviewed in Vyunova (2018). The clinical signatures follow these mechanistic differences. The bulk of Selank's Russian clinical record concerns generalized anxiety disorder and neurasthenia, including controlled comparisons against benzodiazepines and dose-optimization work (Medvedev 2015; Zozulya 2008). Semax's clinical record is concentrated in acute ischemic stroke, vascular cognitive impairment, and optic nerve atrophy — a different indication landscape. A functional connectomic study reported distinct effects on resting-state brain network organization for each peptide (Panikratova 2020), reinforcing the picture that the two compounds, despite shared scaffolding, act on different circuit endpoints. Finally, the depth of the reference base on file differs: Selank has 22 references in the platform record, Semax has 6.

Head-to-head clinical evidence

There are no head-to-head human clinical trials comparing Selank to Semax in the dossier — the head_to_head_candidates set is empty, and the union references include no Russian or Western comparative RCT in patients. The closest direct comparisons are preclinical and mechanistic. Yasenyavskaya (2022) administered Semax and Selank (each 100 mcg/kg/day) in an animal "social stress" model and reported that both peptides restored delayed-type hypersensitivity and direct-agglutination titres in aggressors and submissive animals, with effect sizes broadly similar across the two compounds in that protocol. Kost (2001) measured both peptides in the same human-serum enkephalinase inhibition assay, providing a paired biochemical readout. Panikratova (2020) used a functional connectomic framework to characterise the two peptides side-by-side. Beyond these three direct comparisons, the comparison must be assembled indirectly from single-peptide studies. Each is consistent with the mechanistic split described above — Selank pulling on GABAergic and immunomodulatory pathways, Semax pulling on melanocortin–BDNF pathways — but the absence of a comparative clinical trial means no efficacy gradient between them is established in the literature on file.

Safety profile comparison

The two peptides share a similar reported adverse-event signature in the available Russian literature. Both are intranasal, and both list nasal irritation, mild headache, and (rarely) hypersensitivity reactions to formulation components such as benzalkonium chloride as the most commonly reported issues. Neither has a documented boxed warning. Selank's clinical record specifically notes the absence of sedation, psychomotor impairment, tolerance, or withdrawal at approved 10–14-day protocol durations — properties highlighted in a sedative-hypnotic review that placed Selank alongside GABA-A-modulating compounds (Doyno 2021). Semax has reports of dose-related irritability or restlessness at the higher end of dosing per the source-bundle summary, plausibly linked to its monoamine-modulating profile (Eremin 2005). Both peptides have contraindications listed in Russian product labeling for pregnancy and breastfeeding on the basis of absent controlled data. The decisive shared caveat is the same for both compounds: the chronic-use safety window beyond the approved 10–14-day to 2–4-week treatment courses has not been systematically characterized, and no large-scale Western post-marketing pharmacovigilance dataset exists.

Indication overview

Selank is registered in Russia (and several CIS countries including Belarus, Kazakhstan, and Ukraine) as a prescription anxiolytic for generalized anxiety disorder and neurasthenia, with Russian regulatory approval dating to 2009 and clinical optimization work continuing under the Russian system (Medvedev 2015). Semax holds Russian (and Ukrainian) prescription approval for a different set of indications — acute ischemic stroke, cognitive disorders including vascular cognitive impairment, and optic nerve atrophy — and has been on the Russian Vital and Essential Drugs List. Neither peptide is FDA-approved, EMA-approved, or recognized as a dietary-supplement ingredient. As of 2026, Semax is the subject of an FDA Pharmacy Compounding Advisory Committee review (relevant to US compounding status, not an approval pathway); Selank is not under any current FDA review. Both peptides exist in Western markets only through research-chemical channels of uncertain identity and purity, which are not equivalent to the pharmaceutical-grade Geropharm intranasal formulations used in the Russian clinical record. Inozemtseva (2024) reported antidepressant-like and antistress effects of Semax in a rat chronic-unpredictable-stress model — illustrating ongoing preclinical work — but this does not change the regulatory status in either jurisdiction.