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These four get lumped together as “cognitive peptides” constantly, but they come from completely different origins and have very different evidence bases. Worth laying out clearly rather than treating them as interchangeable.

Semax

A synthetic heptapeptide based on the ACTH(4-10) fragment, with a Pro-Gly-Pro extension added to strip out the adrenal hormone effects of ACTH while keeping (and enhancing) neuroprotective activity. Research points to upregulation of BDNF and NGF. Semax has a long clinical history and has been registered as a pharmaceutical in Russia for decades — one of the more clinically established compounds in this group.

Selank

Also a synthetic heptapeptide, studied mainly for anxiolytic and immunomodulatory effects via GABAergic and serotonergic pathways. It’s believed to work partly by inhibiting the enzymatic breakdown of enkephalins (endogenous opioid peptides tied to mood regulation). Like Semax, Selank has a long Russian clinical registration history.

Cerebrolysin

Structurally different from the other three — it’s not a single peptide but a complex mixture of peptide fragments derived from processed porcine brain protein. Its defining feature is a multi-target mechanism: rather than acting on one receptor, it’s studied for modulating several neuroprotective and neurorestorative pathways simultaneously. It has a longer pharmaceutical history in stroke and dementia research contexts than any compound here.

Dihexa

Mechanistically the most distinct of the four — it works through the HGF/c-Met axis rather than the pathways above. Important caveat: the widely-repeated claim that Dihexa is “10 million times more potent than BDNF” traces back to a single 2014 study that has since been retracted and can’t be cited as valid evidence. Dihexa remains preclinical only — there are no completed human trials. Treat any vendor page citing that potency figure as outdated or uncritical.

Bottom Line

Semax and Selank have the most established clinical history. Cerebrolysin has real pharmaceutical use in specific contexts but a very different (mixture-based) profile. Dihexa is the least substantiated of the four right now — interesting mechanism, but resting on retracted foundational data and zero human trials.

Explore the Directory

• Semax
• Selank
• Cerebrolysin
• Dihexa

This is a research literature summary, not medical advice. Talk to a licensed healthcare provider about any of these compounds.

Related: How does this compare to non-peptide options? See Peptides vs. Functional Mushrooms for Cognitive Support.

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