Semax vs Selank
Both peptides emerged from the same Russian Academy of Sciences programme in the 1990s and are routinely studied together. The mechanistic overlap is real, but the practical differences are sharp enough to make the choice obvious once you know your research endpoint.
At a glance
| Semax | Selank | |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Parent molecule | ACTH(4-10) fragment | Tuftsin (Thr-Lys-Pro-Arg) |
| Primary endpoint | Cognition, attention, neuroprotection | Anxiolysis, anti-asthenia, immunomodulation |
| Mechanism (primary) | BDNF/NGF induction | Enkephalinase inhibition |
| Route | Intranasal | Intranasal |
| Onset | Hours to days | 30–60 min for anxiolytic feel; days for cumulative effect |
| Clinical use (Russia) | Stroke recovery, cognitive impairment | Generalised anxiety, adjustment disorder |
| UK status | Research chemical | Research chemical |
When researchers pick one over the other
Reach for Semax when…
- · The endpoint is memory, learning, or sustained attention.
- · The research model is ischaemic neuroprotection or post-stroke recovery.
- · You want BDNF/NGF induction as the molecular handle.
- · The protocol prioritises cognitive performance under load.
Reach for Selank when…
- · The endpoint is anxiety, stress reactivity, or anti-asthenic effect.
- · You want anxiolysis without sedation or motor impairment.
- · The mechanism of interest is enkephalin-system modulation.
- · Immune-axis modulation is part of the research question.
The Semax + Selank stack
Combining the two peptides is one of the most-replicated approaches in published Russian research — and the rationale is straightforward: the mechanisms are different enough that there is little redundancy. Semax drives BDNF/NGF induction and cognitive performance; Selank elevates endogenous enkephalin tone and dampens anxiety without affecting alertness. Stacked, they cover both axes of the cognition-mood interaction. Most published protocols stagger administration (Semax earlier in the day, Selank spread or pre-stressor) rather than co-administering.
Origin and development
Two arms of the same Russian nootropic-peptide programme
Both Semax and Selank emerged from the Russian Academy of Sciences peptide research programme that ran through the 1980s-90s at the Institute of Molecular Genetics. The programme's approach was to identify short peptide fragments derived from larger endogenous hormones or immune-system peptides, then engineer stable analogues that retained the target pharmacology of the parent while acquiring practical pharmacokinetic properties suitable for research and clinical use.
Semax was engineered from ACTH(4-10), the classical cognitive-effect fragment of adrenocorticotropic hormone that had been extensively characterised in the De Wied laboratory memory-modulation research programme. Selank was engineered from tuftsin, the immune-system tetrapeptide fragment of immunoglobulin heavy chain. The two parent starting-scaffolds provide distinctive mechanism-of-action angles that carry through to the engineered analogues — Semax's cognitive-effect scaffold produces the cognitive positioning, Selank's immune-modulation scaffold produces the immune-modulation angle alongside the anxiolytic effects.
Both compounds received Russian regulatory approval in the 1990s and have substantial Russian clinical evidence bases — Semax for post-stroke and cognitive-support indications, Selank for generalised anxiety disorder. Neither has UK MHRA or EMA-central licensed use; both are research chemicals in Western contexts.
Mechanism-of-action comparison
BDNF/NGF induction versus enkephalinase inhibition
Semax's primary mechanism-of-action is BDNF/NGF induction — the compound increases hippocampal and cortical BDNF and NGF expression, which in turn supports synaptic plasticity and cognitive-endpoint effects. Additional mechanism-of-action angles include monoaminergic modulation (particularly dopaminergic and serotonergic effects) and enkephalinase inhibition (partial, contributing to the mood-modulation effects).
Selank's primary mechanism-of-action is enkephalinase inhibition — the compound reduces enzymatic degradation of endogenous enkephalin peptides, elevating endogenous enkephalin tone and producing anxiolytic effects through the opioid-system-adjacent mechanism. Additional mechanism-of-action angles include GABAA receptor allosteric modulation (contributing further to the anxiolytic effects), BDNF induction (contributing to the cognitive-support effects), and immune-system modulation (contributing to the anti-asthenic effects).
The overlap between the two compounds is substantial (both include BDNF-induction and enkephalinase-inhibition angles) but each has distinctive primary mechanism-of-action angles unshared by the other. This overlap-and-distinctness structure is the mechanistic basis for the classical Semax + Selank stacking approach — the shared mechanism angles provide cognitive-and-mood coverage, and the distinct primary mechanisms provide complementary cognitive-and-anxiolytic research-tool positioning.