Selank vs semax: two Russian peptides built on the same tail, tested for different things, and compared head to head exactly once

Same family, different jobs. Both were made in Russia by taking a short active fragment of a natural peptide and attaching the tripeptide Pro-Gly-Pro to stop enzymes destroying it. Semax starts from a fragment of ACTH; selank from a fragment of the immune peptide tuftsin.

What each was tested for. Semax in acute stroke, optic-nerve disease, motor neurone disease and attention. Selank in generalised anxiety and neurasthenia, usually against or alongside a benzodiazepine. The trials are Russian, small, and run from 27 to 60 people.

They have been compared once. A 2020 study gave semax, selank or placebo to 52 healthy participants and scanned them. It found shared and distinct effects on connectivity between the amygdala and the right temporal cortex. It measured brains, not symptoms.

What people actually buy is not what was studied. The Western market sells N-acetyl semax amidate and N-acetyl selank amidate, modified versions with no trial evidence of their own.

Status. Registered medicines in Russia. Approved nowhere else, and sold elsewhere as research chemicals.

In 2020 a Russian group gave a single injection of semax, of selank, or of placebo to 52 healthy volunteers and performed resting-state functional MRI three times: before, five minutes after, and twenty minutes after. The regions chosen were the amygdala, which governs anxiety, and the dorsolateral prefrontal cortex, which governs working memory.

The result was a difference in connectivity between the right amygdala and a region spanning the fusiform, inferior and middle temporal and parahippocampal gyri, with what the authors describe as both general and specific effects of the two compounds. In plain terms: the two peptides did partly the same thing and partly different things to a brain circuit, within twenty minutes, in healthy people.

What it does not tell you is whether either helps anyone. Connectivity in a scanner is not anxiety, attention or recovery from a stroke, the study was single-dose, and the participants were healthy. It is the only human comparison that exists, and it is a mechanism study.

Beyond it, the studies naming both compounds are animal work: a toxicity screen in mouse embryonic stem cells, and a rat study of the shared tripeptide described below.

Short peptides are destroyed in minutes by the enzymes that trim protein ends. The Russian approach to that problem, in both of these compounds, was to bolt a protective tripeptide onto the end: Pro-Gly-Pro, proline-glycine-proline.

Semax is the ACTH fragment 4-7, the part of adrenocorticotropic hormone with behavioural rather than hormonal activity, plus Pro-Gly-Pro. It does not raise cortisol, which is the point of using that fragment rather than the whole hormone.

Selank is a tuftsin analogue, a fragment of an immunoglobulin-derived immune peptide, plus Pro-Gly-Pro. Its anxiolytic effects are described as benzodiazepine-like without sedation or dependence, and it is the compound with the anxiety trials.

The tail is not inert. A 2014 rat study in this ledger examined Pro-Gly-Pro's own effect on brain gene expression after ischaemia, noting that it is the C-terminal fragment of both drugs. So part of what either compound does may be attributable to the piece they share, which is an unusual thing to be able to say about two compounds people compare as alternatives.

A fourth selank row stood here until 2026-09-24, citing a 2012 case series in obsessive-compulsive disorder. The paper behind it is about low-dose lithium augmentation in venlafaxine-resistant depression and does not concern selank; the compound's record had matched it by alias and this page repeated the attribution. Both are corrected, and no study of selank in obsessive-compulsive disorder is indexed.

Three things are worth noticing. The trials are small, the largest being 60 people. They are almost all Russian, published in Russian-language journals, and have not been replicated elsewhere. And they test conditions almost nobody buying these peptides has: the anxiety trials enrolled diagnosed anxiety disorders, and the semax trials enrolled people who had just had a stroke.

Each compound's full record, with its dosing detail, is here: selank and semax.

The compounds in the trials above are semax and selank as registered in Russia, given as nasal drops or by injection. The compounds sold through Western research-chemical vendors are usually N-acetyl semax amidate and N-acetyl selank amidate: the same core sequences with an acetyl group added at one end and the other end amidated.

Those modifications are not cosmetic. They are made for the same reason the Pro-Gly-Pro tail exists, to slow degradation, and the vendors' claim is that the modified forms are more stable and better absorbed through the nose. No trial has tested either modified form, in any condition, in anyone. There is no published comparison with the parent compounds and no pharmacokinetic study of them in this ledger.

So the evidence on this page describes one set of molecules and the market sells another. A page that quotes the stroke trials next to a product listing for the acetylated version is comparing things that have never been shown to be equivalent.

Both are given intranasally in most of their studies, which is how the Russian registered products are formulated, and by injection in some, including the 2020 imaging study. The semax trials use a percentage solution rather than a milligram figure, 0.1% or 1%, which is how the product is labelled there.

The dose detail for each compound sits on its own record, where it belongs with that compound's sources: semax doses and selank doses. This page does not repeat them, and neither record carries figures for the acetylated forms, because no study has given one.

Both are described as well tolerated in their trials, and the selank literature makes a specific claim: that it produces anxiolytic effects without the sedation, memory impairment and dependence that benzodiazepines cause, which is why its trials are run against or alongside phenazepam.

The evidence behind those reassurances is thin in three ways. The trials are small, so uncommon effects would not appear. They are short, so nothing is known about months or years of use. And they studied the registered products rather than the acetylated forms most people take.

The one toxicity study in this ledger that names both is a screen in mouse embryonic stem cells, which found that selank altered the proportion of cells differentiating into GABA-producing neurons. That is a signal in a dish about developing cells, not a finding about adults, and it is the kind of result that would prompt further work rather than conclusions.

Nothing in people. The pair is sold together as a single nasal spray by at least one vendor ranking for this query, and the stack is a staple of nootropic forums, and no study has given both to the same person to see what happens.

The rationale offered is that they do different things, one calming and one activating, which the 2020 imaging study partly supports in the narrow sense that their effects on one circuit were not identical. That is a long way from evidence that combining them is useful or safe.

The one consideration specific to this pair is the shared tail. If part of either compound's activity comes from Pro-Gly-Pro, then taking both is a larger dose of that fragment, which nobody has studied deliberately.

Both are registered medicines in Russia, semax for stroke and cognitive indications and selank as an anxiolytic. That registration rests on the Russian trial record and is not recognised elsewhere.

Neither has been approved by the FDA, the EMA or any comparable regulator, and neither has been through the kind of trial programme those regulators require. Outside Russia they are sold as research chemicals, with the usual consequence that no regulator has assessed what is in the bottle.

Neither appears on the World Anti-Doping Agency's prohibited list by name. As unapproved substances they would fall under the category covering drugs with no current regulatory approval for human therapeutic use.

Supported: selank has small randomised trials in diagnosed anxiety disorders, generally as an add-on or comparator to a benzodiazepine. Semax has small controlled trials in acute stroke, optic-nerve disease and motor neurone disease, and raises plasma BDNF. Both alter amygdala connectivity within twenty minutes of a single dose in healthy people, in partly different ways.

Not supported: that either outperforms the other for anything, since the only comparison measured brain scans; that results in stroke or diagnosed anxiety transfer to a healthy person wanting focus or calm; that the acetylated forms sold in the West behave like the studied compounds; that the pair works better than either alone.

If the question is which has evidence closest to what people want them for, the answer is selank, because anxiety in diagnosed patients is nearer to the use case than acute stroke is. That is a statement about how far the evidence has to be stretched, not about which compound works.

Other pairs are set out the same way in the comparison directory, and every compound on this site has its own cited record in the compound directory.

1. Saying no study has compared them. One has, in 52 healthy people, and it measured connectivity rather than symptoms.
2. Quoting the trials for the acetylated forms. N-acetyl semax amidate and N-acetyl selank amidate have no trial evidence; the studies used the Russian registered products.
3. Reading the stroke trials as cognitive-enhancement evidence. They enrolled people recovering from a stroke.
4. Treating Russian registration as equivalent to FDA or EMA approval. It rests on a different evidence standard and is not recognised elsewhere.
5. Assuming the stack is complementary. Nothing has tested the pair, and they share a tail whose own activity is documented.
6. Calling selank a benzodiazepine substitute. Its trials compared it with phenazepam in small groups; that is a comparison, not an established equivalence.