Semax vs Selank: Two Peptides, Two Parent Molecules

Semax and Selank get compared constantly, usually as if they were two settings on the same dial. They are not. They came out of the same building in Moscow, they share one structural feature, and almost everything else about them starts from a different molecule and runs through a different research literature.

This post covers where each one came from, what each is chemically, where the mechanisms actually diverge, what the N-acetyl and amidate labels mean, and what the regulatory status is in plain terms. All products discussed here are supplied for laboratory and research use only. Nothing below is dosing, administration, or usage guidance.

Same lab, same decade, different starting molecules

Both compounds trace back to the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow, with work associated with Ivan Ashmarin and Nikolai Myasoedov. The design philosophy was consistent across both projects: take a short endogenous peptide fragment that already has known activity, then bolt a proline-glycine-proline tail onto it so the resulting molecule survives longer in plasma.

That is where the similarity ends. The fragments they started from are unrelated.

Semax was developed in the 1980s from a fragment of adrenocorticotropic hormone (ACTH) and entered the Russian state register of medicines in the 1990s. Selank came later, in the 1990s, built from tuftsin, an immunomodulatory tetrapeptide that occurs as a fragment of the immunoglobulin G heavy chain. Selank was registered in Russia in the 2000s.

So one is an ACTH derivative. The other is an immune-peptide derivative. Comparing them as interchangeable “Russian nootropic peptides” flattens a real chemical distinction.

What Semax is

Semax is a heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro. The first four residues are the ACTH(4-7) fragment; the literature typically describes the molecule as an ACTH(4-10) analog. The Pro-Gly-Pro tail is the synthetic addition.

The important structural point: the fragment Semax is built from is the part of ACTH that does not carry corticotropic activity. Full ACTH signals the adrenal cortex to release cortisol. The 4-7 fragment does not. This is why the published work on Semax sits in the neuro-signaling literature rather than the endocrine literature.

Research on Semax has concentrated on neurotrophin expression, particularly brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF), along with downstream TrkB signaling. Rodent studies have reported changes in hippocampal and cortical expression of neurotrophin-related genes, and a separate line of work has examined gene expression related to vascular and immune response in models of focal cerebral ischemia. Modulation of dopaminergic and serotonergic systems also appears in the literature.

WWP supplies Semax as lyophilized powder in 5mg and 10mg presentations. See the Semax product page for current specifications.

What Selank is

Selank is also a heptapeptide: Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues are tuftsin (Thr-Lys-Pro-Arg). The same Pro-Gly-Pro tail is appended.

Tuftsin’s native role is immunological. It is a phagocytosis-stimulating fragment released from IgG. That heritage shows up in Selank’s research profile, which includes reported effects on cytokine and interferon-related gene expression alongside the neuro work.

The neuro literature on Selank is dominated by the GABAergic system. Published studies have examined effects on GABA-A receptor subunit gene expression, behavior in standard rodent anxiolytic models such as the elevated plus maze, and monoamine metabolism. A separate and frequently cited line of work concerns enkephalin degradation: both peptides have been reported to inhibit enkephalin-degrading enzymes in human serum, and in the study that measured both, Semax was the more potent inhibitor of the two. This is a shared mechanism, not a point of divergence, though it is cited far more often in the Selank literature.

WWP supplies Selank as lyophilized powder in 5mg and 10mg presentations. See the Selank product page.

Semax vs Selank: side by side

Where the mechanisms actually diverge

The clean way to hold the difference: Semax is examined mostly through what cells build, and Selank mostly through how signals are damped.

The Pro-Gly-Pro tail, and why both have one

Short peptides do not last long in circulation. Exopeptidases chew them from both ends: aminopeptidases from the N-terminus, carboxypeptidases from the C-terminus.

The Pro-Gly-Pro tripeptide appended to both molecules is a stability device. Proline-containing sequences are poor substrates for many peptidases, so the tail slows enzymatic breakdown of the active fragment ahead of it. It is the single design element the two compounds genuinely share, and it is a formulation-chemistry decision rather than a mechanism of action.

This is a common pattern across research peptides. The same instinct - modify the ends of a short peptide so it survives longer - drives most of the derivative naming you see in this category, including the compounds covered in our BPC-157 vs TB-500 comparison.

Decoding the names: N-acetyl, amidate, and what they change

Around 880 searches a month go to “N-acetyl semax amidate,” and a similar cluster exists for the Selank equivalent. Most pages that rank for those terms never explain what the words mean chemically.

Two separate modifications are being described:

N-acetyl means an acetyl group has been attached to the free amino group at the N-terminus of the peptide. Acetylation removes the free amine that aminopeptidases recognize, which slows degradation from that end.

Amidate (or amidated) means the C-terminal carboxylic acid has been converted to a carboxamide. This removes the free carboxyl group that carboxypeptidases recognize, which slows degradation from the other end.

Put together, N-acetyl semax amidate is Semax with both termini blocked. The core sequence is unchanged. It is a different chemical entity from plain Semax, with a different molecular weight and a different mass-spec signature, and it should be labeled as such by the supplier.

That last point matters commercially. “Semax,” “N-acetyl semax,” and “N-acetyl semax amidate” are three different compounds sold under names that look almost identical in a product listing. The Certificate of Analysis is what tells you which one is actually in the vial - the stated molecular formula and mass on the COA either matches the modified structure or it does not. If a supplier lists a modified variant but the COA reports the mass of the unmodified peptide, those are two different products.

Regulatory status, stated plainly

Both compounds are approved pharmaceuticals in Russia, prescribed there under their registered indications. Neither is approved by the FDA in the United States. Neither is a scheduled controlled substance under US federal law. Both spent late 2023 to early 2026 on FDA’s Category 2 compounding list - the agency’s stated concern for Semax being precisely the naming ambiguity this post describes, with multiple salts and derivatives sold under one common name - before being removed from that category in April 2026, with Semax among the compounds referred for advisory committee review.

In the US market, both are sold as research chemicals for laboratory and research use only. They are not intended for human consumption, ingestion, injection, or therapeutic use. A large share of consumer search interest around these two compounds relates to nasal-spray formats sold in other markets. WWP does not supply those formats and provides no administration or usage guidance of any kind.

What to check when sourcing either one

The Semax and Selank market has a specific failure mode: near-identical product names covering chemically different molecules, sold at prices that vary by 3x with no stated reason. Three checks handle most of it.

Read the COA, not the product title. Confirm the molecular formula and observed mass match the compound you are ordering, including the acetyl and amide modifications if the listing claims them. Purity by HPLC should be stated as a number, not as an adjective. Our COA library is public if you want a reference for what a complete document looks like.

Confirm the presentation. Both compounds ship from WWP as lyophilized powder in 10-vial packs, at 5mg or 10mg per vial. Compare per-vial cost at the same milligram strength or the comparison is meaningless.

Check whether the supplier will stand behind the number. Every batch is ≥99% purity. Send us a COA from any independent test and we’ll issue store credit regardless of what it shows.

Frequently asked questions

Why do studies examine Semax and Selank together?

Because they came out of the same research program and share the same Pro-Gly-Pro stabilizing tail, published work has sometimes examined them in parallel to compare how two differently-derived heptapeptides behave under the same experimental conditions. The pairing in the literature is largely a function of shared origin and shared design approach, not evidence that the two act on the same pathway. Their parent molecules and dominant mechanisms are different.

Which is better for anxiety, Semax or Selank?

That question cannot be answered as stated, and WWP makes no claims about either compound. What the published record shows is a difference in where the research sits. Anxiolytic-model studies - elevated plus maze and similar rodent paradigms - are concentrated on Selank, which follows from its tuftsin parent and its reported effects on GABA-A receptor subunit expression and enkephalin degradation. The Semax literature is concentrated on neurotrophin expression and cognition-related models instead. Those are different research questions with different endpoints, so the two bodies of work do not produce a head-to-head answer.

Is Semax legal in the USA?

Semax is not an FDA-approved drug in the United States and is not a scheduled controlled substance. It is sold in the US as a research chemical for laboratory and research use only, not for human consumption. Import and resale rules vary, and this is not legal advice.

Does Semax affect hormone levels?

Semax is built from the ACTH(4-7) fragment, which is the portion of adrenocorticotropic hormone that does not carry corticotropic activity. Full ACTH signals cortisol release from the adrenal cortex; the fragment used in Semax does not, and that was the point of choosing it. This is why the published work sits in neuro-signaling rather than endocrine research.

Why does depression appear in Semax search results?

Russian clinical literature examined Semax across several neurological and psychiatric contexts during and after its registration there, and those citations propagate through search results. Those studies were conducted under a different regulatory framework and do not constitute an approved indication in the United States. WWP makes no therapeutic claims about either compound.

What is the half-life of these peptides?

Both are short peptides subject to rapid enzymatic degradation, which is the reason the Pro-Gly-Pro tail exists and the reason the N-acetyl and amidate variants were developed. Reported values vary by study, model, and analytical method. The published pharmacokinetic literature is the appropriate source, and WWP does not publish pharmacokinetic parameters for research compounds.

Are Semax and Selank the same class of compound?

Only in the loose sense that both are synthetic heptapeptides from the same laboratory tradition. Structurally they share three residues out of seven, and those three are the appended stabilizing tail rather than the active fragment. Their parent molecules, one a pituitary hormone fragment and one an immune peptide fragment, place them in different classes.

The bottom line

Semax and Selank are a bad pair to think of as competitors. They are two applications of one design idea - stabilize a short endogenous fragment with a Pro-Gly-Pro tail - applied to two unrelated starting molecules, producing two separate research literatures.

If you are sourcing either one, the chemistry that matters most in practice is the naming. Confirm on the COA whether you are buying the base peptide or an N-acetyl amidated variant, because the listings look nearly identical and the molecules are not. Current specifications are on the Semax and Selank product pages, and every batch we ship has a document behind it in the COA library.

All products are supplied for laboratory and research use only. Not for human consumption.