Dr. Tharindunee JayakodyPhDSemax and Selank are synthetic peptides that show cognition modulatory effects and anxiolytic-like effects as well as neurotrophic signaling in animal models. Similarly, other short peptides with neuromodulatory effects such as DSIP, PE-22-28, VIP and N-Acetyl Semax have also been discussed in some literature, grouping them based on their common "nootropic" properties. Sections below discuss some of the available literature, mostly describing a mix of molecular, animal, and limited human findings, mostly coming from the Russian scientific community. It is important to note that these compounds are still being investigated for the above effects and nothing below is a statement on outcomes in people.
These peptides do not belong to one receptor family nor elicit a single outcome according to any available validated pharmacological classification. Rather, they appear in scientific literature connected to various neuromodulatory effects, sometimes with shared functions in learning and memory. They upregulate the expression of neurotrophins such as BDNF and NGF and modulate ion channels and related signaling proteins pertaining to neuronal firing, according to animal studies. Thus, in animal models, they show effects on inhibitory neurotransmission, and behavioral readouts pertaining to stress, depression, anxiety or memory and learning. Semax is commonly described as an ACTH-derived heptapeptide with a sequence of Met-Glu-His-Phe-Pro-Gly-Pro. Selank is a synthetic tuftsin analog with a sequence of Thr-Lys-Pro-Arg-Pro-Gly-Pro. Both these peptides were developed in Russian research settings that generated most of the human data. Similar short peptides that show neuromodulatory effects are also discussed in the literature, such as the delta sleep-inducing peptide (DSIP), and PE-22-28, a seven amino acid peptide that shows inhibition of TREK-1 channels and antidepressant-like behavior in mice.
In rats, a single intranasal application of Semax increased hippocampal BDNF protein, trkB tyrosine phosphorylation, and BDNF and trkB mRNA levels, alongside improved performance in conditioned avoidance testing [1]. A peptide with a similar function is vasoactive intestinal peptide (VIP), which potentiated glutamate-linked BDNF expression in primary cultured cortical neurons and astrocytes of mouse [2].
In human serum in vitro, Semax and Selank inhibited enkephalin-degrading enzymes in a dose-dependent manner, with IC50 values of 10 µM and 20 µM respectively — more potent than puromycin or bacitracin in the same assay [3]. Enkephalins are known natural anxiolytics. The authors suggest that one mechanism by which the anxiolytic and cognitive effects of the peptides could be elicited is by maintaining enkephalin levels. Although human serum was used in this study, this cannot be accounted as human clinical evidence, as different pharmacological parameters must be considered and evaluated during a human clinical trial to establish that. A similar observation was reported in BALB/c mice, which showed anxiolytic behaviour together with an increased half-life of plasma leu-enkephalin, while the same study found no effect of Selank on behaviour or enkephalinase activity in C57Bl/6 mice [4]. In a separate in vivo rat study, Selank administration altered the expression of genes involved in GABAergic neurotransmission in the frontal cortex, with the pattern of change resembling that produced by GABA itself, supporting a plausible link to anxiolytic-like pharmacology [5].
The clearest split in this literature is between extensive animal and in vitro work and a much smaller human literature. For Semax, the strongest data are rodent studies of gene expression, learning-related behavior, and neuroprotection, while human reports are comparatively sparse and often embedded in Russian-language clinical traditions. For Selank, human studies exist — including a comparative trial in 62 patients with generalised anxiety disorder and neurasthenia, in which Selank produced anxiolytic effects broadly similar to medazepam [6] — but they are few, region-specific, published in Russian, and not broadly replicated in large multinational programs. DSIP is even less secure as a translational candidate, with its underlying biology and its original sleep-factor hypothesis both remaining unresolved despite older animal and human observations.
Although the short peptides discussed above are grouped as a single class in various literature, they differ substantially in sequence, origin, target biology, and mechanisms of action, sharing mainly the limited length of the amino acid chain. Semax has the strongest association with BDNF/NGF signaling in preclinical work, Selank with anxiolytic and GABA-linked studies, DSIP with sleep and neuroendocrine uncertainty, and PE-22-28 with TREK-1 and antidepressant-like behavior in animal models. Another limitation is that many human reports are confined to a single geographic area, making generalizability and independent replication important unresolved questions.
Two Semax derivatives illustrate the same limitation from a different direction. N-Acetyl Semax has been characterised largely in vitro, with reported changes to metal-binding and redox behaviour relative to the parent peptide. Adamax, an adamantane-modified Semax analogue, has almost no independent literature of its own — the available preclinical evidence describes Semax rather than the derivative. In both cases the parent peptide's evidence base is doing most of the work, and effects should not be assumed to transfer to a modified sequence without direct study of that sequence.
The most useful next step in validating these peptides would be to determine clearer mechanistic separation and to reproduce published effects in more independent studies. For example, linking Semax-induced changes in expression of the neurotrophic factors BDNF and NGF to behavioral readouts in animal models and in human tissues would strengthen the evidence base. For Selank, reproducing the modulation of GABA-related gene expression and inhibition of enkephalin degradation in both animals and human tissues would help determine whether there are species-specific effects on behavior. For DSIP, PE-22-28, VIP, N-Acetyl Semax and Adamax, the field would benefit from conclusive data on peptide-receptor interactions, standardized assays showing reproducible activity data, and biochemical effects coupled with independent in vivo studies to validate their functions across species.
Taken together, Semax and Selank are neuromodulatory peptides that have shown, in preclinical models, effects on gene expression, neurotrophic signaling, inhibitory neurotransmission, and behavioral readouts related to anxiolytic and cognitive properties. The evidence has yet to be reproduced consistently across species. Semax is most strongly associated with preclinical BDNF/NGF studies, Selank with anxiolytic and GABA/enkephalin-linked findings plus a limited human literature, and DSIP, PE-22-28, VIP, N-Acetyl Semax and Adamax each occupy more specific or less settled niches within the same research ecosystem.
For a closer look at the two most-studied compounds in this class, see our dedicated posts: Semax Research: BDNF Signaling and Neuroprotection and Selank Research: GABAergic Signaling and Anxiolytic Peptide Biology.
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WRITTEN BY
Dr. Tharindunee Jayakody
PhD — Scientific Contributor and Reviewer
Dr Jayakody is a molecular pharmacologist with over 15 years of experience in translating complex research into clear, evidence-based explanations, with expertise on peptide therapeutics and other emerging compounds, particularly in delineating the mechanisms of action of therapeutics. As a contributor to research-focused platforms, Dr Jayakody aims to give scientifically literate readers a balanced view of what current data can and cannot support, helping them understand how promising findings in the lab translate, or sometimes fail to translate, into real-world applications.
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Preclinical Selank research on GABAergic signaling, enkephalin mechanisms and anxiolytic peptide biology, with evidence clearly tiered. Research use only.
An evidence-led look at Semax research into BDNF and neurotrophic signaling, covering cerebral ischemia models, enkephalin-degrading enzyme inhibition, and the peptide's clinical registration context in Russia.
