Semax vs Selank: How the Two Neuropeptides Compare

Semax and Selank are sibling peptides. Both were developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, both are seven amino acids long, and both end in the same stabilizing Pro-Gly-Pro tail. What separates them is where their first four residues come from, and that changes what researchers study them for.

This guide compares the two side by side: their origins, the key rat and clinical studies, what “NA” means on a label, the limits of the evidence, and what to check when sourcing them in Canada.

Same lab, same tail

Short natural peptides tend to be broken down within minutes, which makes them hard to study. The Moscow group’s solution was to add a three-residue tail, proline–glycine–proline, that slows that breakdown. They applied it to two different starting fragments. Semax borrows its first four residues from ACTH, the pituitary hormone that controls cortisol release. Selank takes all four residues of tuftsin, a small peptide cut from immunoglobulin G antibodies.

Semax: an ACTH fragment without the hormone

ACTH normally tells the adrenal glands to release cortisol. Its 4–10 fragment, Met-Glu-His-Phe-Arg-Trp-Gly, was known to act on the brain without that hormonal role. Semax keeps the first four residues of the fragment and replaces the last three with Pro-Gly-Pro, giving a peptide described in the research literature as devoid of ACTH’s hormonal activity.

The most-cited mechanistic study, published in 2006, gave rats a single intranasal application of Semax and then measured the hippocampus, a brain region central to memory. BDNF protein, a growth factor involved in learning and neuron survival, rose about 1.4-fold. Activation of its receptor, TrkB, rose about 1.6-fold, and the treated rats made more conditioned avoidance responses in a learning task. Other Russian studies have examined Semax in models of reduced blood flow to the brain.

Semax is registered in Russia and appears on the country’s list of vital and essential medicines. Its exact mechanism is still debated; proposals include interactions with melanocortin receptors and effects on enzymes that break down other neuropeptides.

Selank: tuftsin with a stabilizing tail

Tuftsin is a four-residue peptide, Thr-Lys-Pro-Arg, released from the heavy chain of immunoglobulin G and known for immune-modulating activity. Selank extends it with the same Pro-Gly-Pro tail used in Semax.

In a 2016 rat study, researchers tracked 84 genes involved in GABA signalling in the frontal cortex after giving Selank or GABA itself. Expression of dozens of those genes shifted within hours, and the pattern after Selank correlated with the pattern after GABA. That supports the idea that Selank works partly through GABA-related signalling, the same system benzodiazepines act on.

The most-cited clinical comparison, published in 2008, followed 62 patients with generalized anxiety disorder or neurasthenia: 30 received Selank and 32 received the benzodiazepine medazepam. The authors reported similar anxiety-reducing effects in both groups. Selank was registered in Russia in 2009.

Side-by-side comparison

What NA and amidate mean on a label

Many suppliers also sell modified versions. “NA” stands for N-acetyl, a small acetyl cap on the first amino acid; “amidate” means the final carboxyl group has been converted to an amide. Both changes are meant to slow breakdown by enzymes that trim peptides from their ends.

Most of the published research summarized here used unmodified Semax and Selank, so results don’t automatically carry over to the modified forms. Treat NA versions as related but distinct compounds, and expect a different mass on the COA: acetylation adds about 42 g/mol.

SemaxThe unmodified heptapeptide used in most published studies.View product and COA NA SemaxN-acetylated Semax for stability-focused work.View product and COA SelankThe unmodified tuftsin-derived heptapeptide.View product and COA NA SelankN-acetylated Selank for stability-focused work.View product and COA

For multi-compound designs, the Illumineuro blend combines NA Semax and NA Selank with Pinealon and PE-22-28 in one vial.

Limits of the evidence

• One country, one lineage. Development, most studies and both approvals come from Russia, and independent replication elsewhere is limited.
• Small studies. The human trials are small by modern standards, and many are published only in Russian-language journals.
• Animal-to-human gap. Rat gene-expression and behaviour results don’t predict human outcomes on their own.
• Unsettled mechanisms. Neither peptide has a single confirmed receptor target.

Sourcing Semax and Selank in Canada

Pure Peptides Canada is a Canadian-owned supplier of laboratory research peptides, established in 2023. Whichever supplier you use, check:

• Which form you’re getting. Plain, NA and amidated versions have different masses, and mass spectrometry tells them apart: 813.9 g/mol for Semax and 751.9 g/mol for Selank in their unmodified forms.
• A batch-specific COA. The lot number should match your vial. See our COA guide.
• Purity and identity both. HPLC shows purity; mass spectrometry confirms identity. Here’s how they differ.
• Cold, dry storage. Short peptides are sensitive to moisture. Our storage guide covers the basics.

Regulatory status in 2026

At its July 23–24, 2026 meeting, an advisory committee to the US FDA voted 8 to 5 to recommend adding Semax to the list of substances US pharmacies may compound, overriding FDA staff, who had recommended against it. Selank was not part of that review. The vote is advisory only: Semax has not been added to the list and is not an FDA-approved drug. In Canada, Health Canada’s April 2026 advisory on unauthorized injectable peptides did not name either peptide, but it warned that many other unauthorized peptide drugs exist and that “For Research Use Only” labelling does not make such products legal or exempt from regulatory requirements.

Frequently asked questions

Prepared by Pure Peptides Canada. Sources checked October 2026. For laboratory research use only; not for human or veterinary use. This article summarizes published research for education and is not medical advice. Nothing here is intended to diagnose, treat, cure or prevent any disease.