Semax vs Selank.

Semax is a synthetic heptapeptide (Met-Glu-His-Phe-Pro-Gly-Pro) consisting of the ACTH(4-7) fragment of adrenocorticotropic hormone joined to a C-terminal Pro-Gly-Pro tripeptide. It was developed in the late 1980s/early 1990s at the Institute of Molecular Genetics of the Russian Academy of Sciences and is first described in the scientific literature around 1991. The Pro-Gly-Pro extension stabilizes the otherwise rapidly degraded ACTH fragment without retaining ACTH's hormonal (corticosteroid-releasing) activity, making Semax a "neuropeptide" rather than a hormone.

Selank is a synthetic heptapeptide (Thr-Lys-Pro-Arg-Pro-Gly-Pro) developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, with the laboratory designation TP-7. It is a stabilized analog of tuftsin, an endogenous immunomodulatory tetrapeptide (Thr-Lys-Pro-Arg) derived from the Fc region of immunoglobulin G; the added Pro-Gly-Pro tail confers resistance to enzymatic degradation. It is studied primarily as an anxiolytic and nootropic agent and is most associated with Russian neuropharmacology research.

Semax is structurally derived from ACTH(4-10) but lacks the melanocortin-receptor-driven hormonal effects of full-length ACTH, so it does not stimulate cortisol release. Mechanistic (largely rodent and in vitro) work indicates it upregulates brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the hippocampus, and modulates expression of NGF and other neurotrophic and immune-response genes, which is proposed to support neuronal survival and synaptic plasticity. A separate biochemical mechanism is inhibition of enkephalin-degrading enzymes in human serum (reported IC50 ~10 µM), which may prolong the activity of endogenous regulatory peptides. The relative contribution of each pathway to any observed clinical effect remains unsettled; Wikipedia and reviews note the precise mechanism of action is not definitively established.

Selank's parent peptide tuftsin acts on immune cells, and Selank retains immunomodulatory activity while shifting toward neuromodulation. Proposed central mechanisms include modulation of monoamine systems (serotonin, dopamine, noradrenaline) and interaction with the GABAergic and enkephalin/opioid systems; Selank has been reported to inhibit enkephalin-degrading enzymes, prolonging the action of endogenous enkephalins. It has also been reported to influence expression of brain-derived neurotrophic factor (BDNF) and to alter cytokine balance (e.g., IL-6 and interferon-related signaling). These mechanisms are largely characterized in rodent and in vitro models rather than established in humans.

Human evidence comes almost entirely from Russian clinical research and is modest in scale. A representative controlled study by Gusev, Martynov and colleagues (Zh Nevrol Psikhiatr Im S S Korsakova, 2018; PMID 29798983) in 110 ischemic-stroke patients reported that semax plus early rehabilitation raised plasma BDNF and improved motor recovery and functional independence (Barthel index). The strongest mechanistic data, BDNF/TrkB upregulation (Brain Research, 2006; PMID 16996037) and neuroprotection and immune-gene regulation in rat ischemia (Mol Genet Genomics, 2017; PMID 28255762), are preclinical (rat/in vitro). Proposed uses such as ADHD or cognitive enhancement rest largely on hypothesis papers (e.g., Med Hypotheses, 2007; PMID 16996699) rather than rigorous trials. Crucially, no large, independent, randomized, double-blind Western trials have replicated the Russian findings, so the human cognitive- and stroke-benefit claims should be regarded as preliminary.

The great majority of Selank evidence is preclinical (rodent and in vitro), covering anxiolytic-like behavior, stress models, immune/cytokine modulation, and tissue effects under chronic stress (e.g., Bull Exp Biol Med studies on rat intestine and liver under restraint/foot-shock stress, and a cytokine study under 'social' stress). Human clinical data are limited and come almost entirely from Russian-language trials and registry approval rather than large, independently replicated, placebo-controlled studies indexed in Western literature; reported uses include generalized anxiety disorder and asthenic/neurasthenic conditions. A frequently cited molecular review (Protein and Peptide Letters, 2018, PMID 30255741) summarizes the proposed biology. Overall, robust, independently replicated human efficacy data are thin, and mechanistic plausibility should not be read as proven clinical benefit.

Russian clinical reports and the intranasal route describe generally good tolerability, with mild nasal/local irritation the most commonly noted complaint; however, these data come from small studies without the long-term, independent safety surveillance expected for Western drug approval. There is no robust characterization of long-term safety, drug interactions, effects in pregnancy, or risks from non-pharmaceutical "research-use" material sold online, which may vary in purity and sterility. Because much of the mechanistic profile (BDNF/neurotrophin modulation, peptidase inhibition) is extrapolated from animal models, downstream effects of chronic human use are essentially unstudied. Product sold by online vendors is not manufactured to pharmaceutical standards and its identity and contaminants are not guaranteed.

Published reports, mostly from the developing Russian groups, describe Selank as generally well tolerated with a notably low sedation, dependence, and withdrawal profile compared with benzodiazepines, but rigorous long-term and large-sample safety data from independent groups are lacking. Because much of the safety record comes from the originating institutions and small studies, the true adverse-event and long-term safety profile in humans is not well established. As a peptide typically administered intranasally in research, purity, contamination, and product-quality concerns apply to non-pharmaceutical material. It has not undergone the comprehensive safety review required for major regulatory approval outside its country of origin.

Semax is approved as a prescription drug in Russia (and appears on Russia's List of Vital and Essential Drugs) for indications including ischemic stroke, transient ischemic attack, and cognitive disorders. It is not FDA-approved and is unscheduled in the United States, where it is sold by online vendors as a research/non-pharmaceutical product; it is not approved or marketed in most countries outside Russia.

Selank is reported to have been registered/approved in Russia (around 2009) for anxiety and asthenic conditions, marketed as an intranasal preparation. It is not approved by the US FDA and is not an approved drug in the EU; outside Russia it is effectively investigational and is widely sold as a research-use-only / not-for-human-consumption chemical. It is not a controlled substance and is not a standard WADA-prohibited agent, but its unapproved status means quality and legality vary by jurisdiction.