Selank and Semax Research Overview: Same Tail, Different Heads

Selank and Semax are both seven amino acids long. Both were developed in Russia. Both end in the same three residues, Pro-Gly-Pro. Put them side by side and the shared tail jumps out. Then look at the other end. Selank's head comes from an antibody fragment. Semax's head comes from a pituitary hormone. That one difference explains why the Selank peptide and the Semax peptide have such different research histories. Here is the overview.

The shared tail: Pro-Gly-Pro

Short peptides do not last long where enzymes are present. Russian peptide chemists addressed this by adding Pro-Gly-Pro (PGP) to the end of an active fragment. The proline-rich tail slows enzymatic breakdown. It also turns out to have activity of its own in some studies; one of the Semax papers below tested PGP alone. When you read either peptide's sequence, the last three letters are this engineering choice. The first four are the message.

Selank

Origin

Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues, Thr-Lys-Pro-Arg, are tuftsin, a natural fragment of immunoglobulin G. Selank is tuftsin extended with Pro-Gly-Pro for stability. So its parent is an antibody, not a brain peptide, which surprises people the first time they hear it.

Research areas

• Anxiety-related behaviour in rodents. Most of the behavioural literature is in rats and mice.
• GABA-related gene expression. Volkova et al., 2016 reported changes in expression of genes involved in GABAergic neurotransmission after Selank in rodents.
• Enkephalin-degrading enzymes. Zozulya et al., 2001 reported that Selank inhibits enzymes that break down enkephalins, and proposed this as a mechanism.
• A small human study. Zozulia et al., 2008 compared Selank with medazepam in 62 patients with generalised anxiety disorder and neurasthenia. The paper is in Russian. The abstract does not describe blinding, so we do not characterise its result.

Proposed mechanism

Not established. Vyunova et al., 2018 review the candidates: inhibition of enkephalin-degrading enzymes, allosteric modulation of GABA receptor binding in radioligand studies, and changes in GABA-related gene expression. Nearly all of this comes from the developing Russian groups.

Semax

Origin

Semax is Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues are ACTH(4-7), a fragment of adrenocorticotropic hormone. Add the Pro-Gly-Pro tail and you have Semax. It is often described as an ACTH(4-10) analog. Importantly, it lacks the hormonal activity of ACTH. The fragment carries the parent's shape without the parent's hormone job.

Research areas

• Cerebral ischemia in rats. Dmitrieva et al., 2010 reported that Semax and Pro-Gly-Pro activated transcription of neurotrophins and their receptor genes after experimental ischemia. Filippenkov et al., 2020 extended this to the whole transcriptome after ischaemia-reperfusion.
• BDNF and TrkB expression. Dolotov et al., 2006 found increased BDNF and TrkB expression in the rat hippocampus.
• Learning and memory in rodents. A recurring theme in the animal literature.
• Alzheimer's-type animal models. Radchenko et al., 2025 studied Semax and a derivative in an animal model of Alzheimer's disease.

Proposed mechanism

The receptor target is not established. The neurotrophin findings above are the strongest thread. In one cell study, Semax did not activate the melanocortin-4 receptor but blunted alpha-MSH signalling, which argues against a simple melanocortin story. Mavrych et al., 2026 place Semax in the wider gerontology peptide literature and note that much of its clinical evidence comes from Russian studies without independent validation.

Registration status, stated exactly

This is the part people ask about most, so here is the wording as the literature supports it, and nothing more.

• Selank: reported as approved in Russia for anxiety. That statement comes from a secondary source citing a Russian paper. No FDA approval was found.
• Semax: registered in Russia and on the Russian government list of vital and essential drugs. Not FDA-approved. Much of its clinical evidence comes from Russian studies lacking independent validation.

In both cases the status describes a Russian pharmaceutical product. It says nothing about research-grade material from any supplier, including us. Our vials are for laboratory research only.

Selank vs Semax at a glance

Item	Selank	Semax
Sequence	Thr-Lys-Pro-Arg-Pro-Gly-Pro	Met-Glu-His-Phe-Pro-Gly-Pro
Head	Tuftsin (IgG fragment)	ACTH(4-7)
Tail	Pro-Gly-Pro	Pro-Gly-Pro
Main research areas	Anxiety-related behaviour, GABA gene expression, enkephalin enzymes	Cerebral ischemia, BDNF/TrkB, learning and memory, Alzheimer's-type models
Status (as reported)	Reported approved in Russia; not FDA-approved	Registered in Russia; not FDA-approved
House code	PTY-SELK-10	PTY-SEMX-10

Why the two get compared

Selank and Semax are often discussed together, and the reasons are practical rather than scientific. They share a country of origin, a decade of development, a research community and the Pro-Gly-Pro tail. Several of the same authors appear on papers about both. That shared history makes them easy to lump together. The literature itself keeps them apart: the Selank papers are about anxiety-related behaviour, GABA and enkephalins, while the Semax papers are about ischemia, neurotrophins and memory models. If you are planning an experiment, start from the research area, not from the pairing.

Where the evidence stops

Three honest limits. First, the behavioural and gene-expression work is in rodents. Second, the human studies are small, in Russian, and often lack described blinding or independent replication. Third, the mechanisms are proposals. Enkephalin enzymes, GABA binding and BDNF are candidate explanations, not confirmed pathways. Good research questions remain on both peptides, and that is why they are on a research shelf.

Formats you will see

Both peptides come as lyophilised powder in 10 mg crimp-sealed glass vials, stored at -20 °C, desiccated. The catalogue also lists spray and dissolving-strip formats for Selank, Semax and a Selank plus Semax combination, as well as an NA-Semax amidate spray, which is a modified derivative rather than Semax itself. These are listed as formats only. Each has its own container, storage conditions and documentation.

Lot testing

Seven residues is long enough for synthesis to leave deletion sequences, so HPLC matters. Mass spectrometry confirms the intact mass, which for Semax includes the methionine at position one, a residue that can oxidise during storage and shift the mass. A certificate that shows both the chromatogram and the mass tells you more than either alone. Each lot's certificate states its measured purity and identity and is linked from the product page. Two quick checks when you open one: the lot number on the certificate should match the vial label, and the reported mass should match the sequence printed on the product page, not just the name.

Frequently asked questions

Why do Selank and Semax both end in Pro-Gly-Pro?

The tail was added to slow enzymatic breakdown of the active fragment. It is a shared engineering choice from the same Russian peptide chemistry tradition, which is why two peptides with unrelated heads carry the same ending.

Is Semax a hormone?

No. Its first four residues come from ACTH, but the literature reports that Semax lacks hormonal ACTH activity. It is studied as a neuropeptide analog, not as a hormone.

Is Selank approved anywhere?

It is reported as approved in Russia for anxiety, based on a secondary source citing a Russian paper. No FDA approval was found. That status applies to a Russian pharmaceutical product, not to research-grade material.

What is the strongest Semax evidence?

The rat work on neurotrophins: increased BDNF and TrkB in the hippocampus and activated neurotrophin transcription after experimental ischemia. The clinical reports exist but come from Russian studies without independent validation.

See it in the catalogue: Selank and Semax.