Semax vs Selank: Nootropic Showdown

Semax and Selank are close cousins. Both came out of the same Russian research programme, both are heptapeptides, both share the same structural modification, and both are delivered intranasally.

What separates them is where they came from. One is built on a fragment of a stress hormone. The other on a fragment of an immune peptide. That difference in ancestry produces two compounds pulling in opposite directions — one toward activation, one toward calm.

The shared design

Both peptides came out of the Institute of Molecular Genetics at the Russian Academy of Sciences, and both were built using the same approach.

Each takes a short biologically active fragment of a larger natural molecule and adds the tripeptide Pro-Gly-Pro to the C-terminal end.

That addition solves the problem that limits most peptides. Free peptides in circulation are cleaved rapidly by peptidases, often within minutes. The proline-rich tail resists that cleavage, extending the molecule’s working life substantially without changing what it does. Both compounds are heptapeptides — seven amino acids — for exactly this reason: a four-residue active fragment plus the three-residue stabilising tail.

Both are also administered intranasally rather than injected, which takes advantage of the nasal route’s relatively direct access to the central nervous system.

Semax: ACTH without the hormone

Semax is derived from ACTH(4-10) — a seven-residue stretch of adrenocorticotropic hormone.

ACTH is the pituitary hormone that signals the adrenal glands to produce cortisol. But researchers had long observed that ACTH also affects attention, learning and memory, and that these effects appeared separable from its hormonal role.

Semax is the result of that separation. It retains the behavioural and cognitive activity associated with the ACTH(4-10) region while lacking the classical corticotropic action — it does not stimulate cortisol release.

In Russia, Semax holds regulatory approval for use in stroke, transient ischaemic attack, traumatic brain injury and cognitive disorders.

How Semax works

BDNF and trkB. This is the best-characterised mechanism. Brain-derived neurotrophic factor supports neuronal survival, synaptic plasticity and the structural changes underlying learning. In rat hippocampus, a single dose of Semax raised BDNF protein by approximately 1.4-fold, phosphorylated trkB — BDNF’s receptor — by around 1.6-fold, and BDNF mRNA by roughly 3-fold.

That pattern is worth reading closely. Increased mRNA means the gene is being transcribed more actively; increased receptor phosphorylation means the signal is being received, not merely produced. The peptide acts on both ends of the neurotrophin pathway.

Nerve growth factor. Semax has also been associated with increased NGF expression, supporting neuronal survival and differentiation.

Monoamine modulation. Effects on dopaminergic transmission are the proposed basis for its influence on focus and motivation, with additional reported effects on serotonergic and noradrenergic systems relating to attention and arousal.

Ischaemia response. Genome-wide transcriptional analysis in a rat focal ischaemia model found Semax altering expression of genes related to immune and vascular function, which fits its Russian clinical indications in stroke.

Selank: tuftsin redirected

Selank is derived from tuftsin, a naturally occurring tetrapeptide that is itself a fragment of the immunoglobulin G heavy chain. Tuftsin’s known role is immunomodulatory — it stimulates phagocytic activity in macrophages and neutrophils.

Adding the same Pro-Gly-Pro tail produced a compound with a different emphasis: primarily anxiolytic, with the immune activity of its parent molecule still present in the background.

In Russia, Selank holds approval as an anxiolytic, indicated for generalised anxiety disorder and neurasthenia.

How Selank works

GABAergic effects. GABA is the brain’s principal inhibitory neurotransmitter and the system benzodiazepines act on. Research has found Selank altering expression of genes involved in GABAergic neurotransmission — a different kind of action from the direct receptor binding benzodiazepines perform. The proposed distinction is that Selank shifts the system’s own signalling capacity rather than binding the receptor itself, which is the suggested reason it produces anxiolysis without the sedation, tolerance and dependence characteristic of benzodiazepines.

Enkephalinase inhibition. Enkephalins are endogenous opioid peptides involved in pain modulation and emotional regulation. They are degraded rapidly by enkephalinase. Selank inhibits that enzyme, extending enkephalin half-life — potentiating an existing internal signal rather than introducing an external one.

Monoamines. Selank has been reported to influence serotonergic and noradrenergic metabolism, consistent with its effects on mood.

Immune modulation. Its tuftsin lineage carries through, with reported effects on cytokine regulation including interleukin-6 and interferon.

BDNF. Like Semax, Selank has been associated with increased BDNF expression, reached through different upstream mechanisms.

The human evidence

Selank holds the more substantial clinical data of the two.

A study in 62 patients with generalised anxiety disorder and neurasthenia compared Selank against medazepam, a benzodiazepine. Selank produced an anxiolytic effect comparable to the active comparator, alongside antiasthenic and psychostimulant effects — the latter being the notable result, since anxiolysis and stimulation don’t usually travel together.

At 62 participants the study is small, and it comes from the Russian literature rather than a Western regulatory programme. It remains a controlled human comparison against an active drug.

Semax’s evidence is weighted toward the mechanistic and preclinical, with its strongest human data coming from Russian stroke research, where its regulatory approval sits.

Direct comparison

Why they get combined

The rationale for using them together follows from the opposing directions. Semax activates — dopaminergic tone, cognitive arousal, neurotrophic signalling. Selank calms without sedating.

Dopaminergic activation on its own can produce restlessness or anxiety in some contexts. The proposal behind the combination is that Selank’s anxiolytic action offsets that while leaving the cognitive effects intact. Both raise BDNF through different routes, so that pathway is reinforced from two directions.

Combination data is preclinical rather than clinical.

Regulatory position

Neither peptide holds approval from the FDA, EMA or MHRA. Both are approved medicines in Russia, where the majority of the research on them has also been conducted. Most published work on both compounds sits in the Russian literature, with limited independent replication in Western research programmes.

Bottom line

Semax and Selank are the same engineering idea applied to two different starting materials — a fragment of a stress hormone and a fragment of an immune peptide, each stabilised with the same proline tail.

Semax works primarily through neurotrophic signalling: BDNF, its receptor, and dopaminergic modulation, with its clinical footing in stroke and cognitive indications. Selank works through GABAergic signalling and endogenous opioid tone, with the stronger human trial record and a profile described as anxiolysis without sedation.

Activation and regulation, from a shared design.