Comparison
Selank vs Semax: Comparing the Research
Two often-confused Russian peptides — distinct in origin and primary effect, with one mechanism in common.
The short version
Selank vs Semax is a common question because the two are often mentioned together — both are small Russian peptides used as research nootropics. They are not the same molecule and should never be treated as interchangeable. Selank is built from tuftsin, an immune peptide, and is studied mainly as an anxiolytic — something that calms anxiety. Semax is built from a fragment of the hormone ACTH and is studied mainly as a neuroprotective and stimulating nootropic, more about focus and brain protection than calm. They do share one trick: both slow down the enzymes that break apart enkephalins, the body's natural stress-easing molecules. Below, this page keeps the two clearly distinct and sticks to what the cited research actually shows about Selank.
Different origins, different primary effects
Selank is a synthetic analogue of tuftsin — the immunomodulatory tetrapeptide Thr-Lys-Pro-Arg cleaved from the IgG heavy chain — extended to the heptapeptide Thr-Lys-Pro-Arg-Pro-Gly-Pro for stability [13]. Its primary studied effect is anxiolytic, centered on positive allosteric modulation of GABA receptor binding [1] and inhibition of enkephalin-degrading enzymes [2].
Semax derives instead from a fragment of adrenocorticotropic hormone (ACTH 4-10) and is studied chiefly as a neuroprotective and cognitive-enhancing peptide. This is the core of the Selank vs Semax distinction: same research lineage and country of origin, but different parent molecules and different lead indications. Conflating them — a frequent error online — misattributes each compound's evidence to the other.
The shared mechanism: enkephalinase inhibition
Where the two genuinely overlap is the opioid-stabilizing mechanism. Both Selank and Semax inhibit enkephalin-degrading enzymes from human serum, a peptidase-inhibition property shared among ACTH- and tuftsin-derived regulatory peptides [8]. By slowing the breakdown of enkephalins, both can stabilize these endogenous anti-stress peptides. For Selank specifically, this enkephalinase inhibition was quantified at an IC50 of roughly 15 µM in human plasma [2], and its behavioral relevance was confirmed when naloxone abolished Selank's effect in rats [9]. This shared mechanism explains why the two are studied in parallel — but it is one common thread, not evidence that they are equivalent.
What this means for reading the literature
When evaluating Selank, the safe rule is to rely only on studies that actually used Selank. The GABA gene-expression work [4], the BDNF finding [3], the immunomodulatory cytokine results [6], and the clinical anxiety data [5] are Selank studies and belong to Selank. Semax has its own separate record. Treating the two as one inflates the apparent evidence for each and obscures their different profiles — Selank as a calm, non-sedating anxiolytic with immune activity, Semax as a neuroprotective nootropic. This site documents the Selank record; it does not extend Selank's evidence to Semax or the reverse.
Studied together in research
Researchers have at times examined the two side by side — the serum enkephalinase study assessed both peptides in the same assay [8]. That kind of comparative work is legitimate and informative, but it compares two distinct molecules; it does not merge them. Any research-context use of one in place of the other rests on extrapolation, not on a study showing the two are interchangeable. The honest reading keeps Selank and Semax as related but separate compounds, each judged on its own evidence.