Overview
Selank and Semax: What Is the Difference
Two Russian peptides that are always named in the same breath: the same length, the same nasal drops, different parent molecules. Where each came from, what each was actually studied for, and how far a Russian approval carries.
PeptideWiki Editorial~8 min
Why the two get confused
Selank and Semax come from the same place — the Institute of Molecular Genetics of the Russian Academy of Sciences — and from the outside they are built alike: seven amino acids, the same Pro-Gly-Pro tail at the end of the chain, nasal drops, a Russian registration. That is where the similarity ends.
Their parent molecules differ. Selank grew out of tuftsin, the short immune peptide Thr-Lys-Pro-Arg. Semax comes from a fragment of adrenocorticotropic hormone: in sequence terms, ACTH(4-7) with the same Pro-Gly-Pro attached — the literature, and our own profile, call it an analogue of the ACTH(4-10) fragment. In both molecules the tail does one job: it makes the peptide far harder to break down. What the molecule does next is decided by its head, and the heads are not the same.
Hence a simple consequence: "which one is stronger" is not a question this pair can answer. What can be compared is the indication each was studied for, the formulation, and the amount of data standing behind it.
| Feature | Selank | Semax |
|---|---|---|
| Origin | Tuftsin analogue (Thr-Lys-Pro-Arg) plus Pro-Gly-Pro | ACTH(4-7) fragment plus Pro-Gly-Pro, without the steroidogenic activity of ACTH |
| Class in the profile | Anxiolytic with an immunomodulatory component | Nootropic and neuroprotective agent |
| What the mechanism section describes | GABAergic tone, serotonin metabolism, BDNF, enkephalin-degrading enzymes, tuftsin immunomodulation | BDNF induction, melanocortin receptors MC3R and MC4R, serotonin and dopamine turnover, antioxidant pathways |
| What was studied in humans | Anxiety disorder and neurasthenia: a randomised comparison against medazepam in 62 patients | Acute ischaemic stroke, optic nerve atrophy, peptic ulcer disease — clinical studies run in Russia |
| Form and route | Intranasal, 0.15% drops | Intranasal, 0.1% and 1% drops — two different medicines in similar bottles |
| Regulatory status | Approved in Russia, sold over the counter since 2017; not approved anywhere else | Approved in Russia, Ukraine and Belarus; not approved outside the CIS |
Selank: an anxiolytic built on an immune peptide
The profile describes Selank as a synthetic heptapeptide anxiolytic: the tuftsin core carries the immune activity, the added Pro-Gly-Pro carries the stability — and, with it, anxiolytic and nootropic properties that native tuftsin does not have.
How its action is explained
The mechanisms are written as studied, not as settled. GABAergic tone is raised indirectly — by inhibiting GABA-transaminase and by increasing GABA-A receptor sensitivity — rather than by potentiating the receptor the way benzodiazepines do. Alongside that: serotonin metabolism, raised BDNF expression, inhibition of the enzymes that degrade enkephalins, and immunomodulation through the tuftsin core.
What was tested in humans
The key clinical study is a randomised comparison against medazepam in anxiety disorder and neurasthenia: 62 patients over 14 days, 30 of them on Selank. The anxiolytic effect was comparable to the benzodiazepine, without sedation, cognitive dulling or a withdrawal syndrome. The publication reports no onset-of-action window, so we do not state one.
Where the data stop
Alcohol and morphine withdrawal are rat studies; no human trial in withdrawal states has been published. "Neuroprotection" rests on a single animal study in which intranasal Selank raised BDNF in the rat hippocampus — no published work shows it reducing neuronal damage in ischaemic or excitotoxic injury. And the injected use that circulates online rests on nothing at all: Selank was registered and tested only as drops.
Semax: a nootropic with a stroke record
Semax shares the stabilising tail and nothing else. Its head comes from ACTH, which gives it a different pharmacology — and one deliberate absence: it does not act on the adrenal MC2R receptor, so it produces no measurable rise in cortisol.
How its action is explained
The primary mechanism in the profile is BDNF induction: mRNA expression in hippocampus and cortex rises two- to fivefold through the gene's exon IV promoter. Around it sit melanocortin receptors MC3R and MC4R, increased serotonin and dopamine turnover, antioxidant and anti-apoptotic pathways, and reduced microglial activation.
What was tested in humans
Russia approves Semax for three separate indications: acute ischaemic stroke (the 1% solution), optic nerve atrophy and peptic ulcer disease. The stroke studies report faster regression of neurological deficit measured on clinical and electrophysiological endpoints — not on imaging measures of infarct volume. Our profile also notes that in the pooled Russian data the benefit appeared in moderate and severe strokes, not in mild ones.
Where the data stop
The best-known use — "for memory and attention" — is the least supported. A review describes Semax stimulating working memory and attention in humans, but no controlled trial quantifying that effect could be located. For ADHD there is no clinical trial at all, only a 2007 hypothesis paper. In a rat model of Parkinson's disease there was no significant effect on motor behaviour, and the neurodegeneration findings are cell-level and in vitro.
Which one was studied for what
Reduce both profiles to a paragraph and the split is clear: Selank was studied where the leading complaint is anxiety, Semax where brain tissue or the optic nerve is damaged. They overlap on BDNF and on the word "nootropic" — and that overlap is what produces the question "which one should I take".
- Anxiety disorder and neurasthenia — Selank's field. A comparison against a benzodiazepine exists; there is one of it.
- Acute stroke, the aftermath of vascular damage, optic nerve atrophy — Semax's field, where it holds registration and clinical work.
- Memory, attention, "productivity in a healthy person" — claimed for both and supported for neither: no trial has dosed a healthy adult for the cognitive effect.
- Sport: Selank does not appear on the WADA Prohibited List. Semax has no ruling of its own — it shares an origin with ACTH, and ACTH itself is banned under category S2. Treat that as unresolved, not as cleared.
The dosage figures in both profiles record what labels and studies describe, not what anyone should take. One practical difference matters more than the rest: Selank has a single strength, 0.15%, while Semax has two — 0.1% and 1% — in similar bottles, and their daily amounts differ by tens of times. Confusing them is not an error of percentages but of multiples.
What no table can show
Both profiles rest largely on Russian literature. The key publications appeared in Russian, the samples run to dozens of patients, and almost nothing has been repeated outside Russia. Selank's registration, as our dosage section puts it, stands on 30 treated patients compared against another drug rather than a placebo, published once.
There is a check anyone can run in a minute: searching ClinicalTrials.gov for either name returns no study of these peptides — the few hits belong to unrelated work. That does not prove the compounds do nothing. It shows precisely where the edge of the available data lies.
An approval in one country is a fact about a regulator, not about the strength of the evidence. It says the paperwork was accepted; it does not stand in for repeated studies.
How to tell preclinical from clinical, how to read dose ranges and how not to mistake a confident tone for data — that is covered separately in how to read peptide data.
In short: a reader's checklist
- Check whose approval sits behind the status: for both of these it is Russian.
- Compare indications, not strength — anxiety for Selank, stroke and the optic nerve for Semax.
- With Semax, always read the strength: 0.1% and 1% are different medicines in similar bottles.
- Remember that "memory in a healthy person" has been tested for neither.
- Do not carry a nasal regimen over to injections: for injections there are no data.
- In sport: Selank is not listed by WADA, Semax's status is unresolved — which is not the same as allowed.
Field-by-field, the two profiles sit next to each other on the Selank vs Semax page. The full write-ups live in the Selank and Semax profiles.
Sources
The primary studies and registries behind the statements above. Both peptides are documented mostly in Russian-language journals, which is itself part of the picture.
- 01PubMed: Selank in generalised anxiety disorder (2008)
the randomised comparison against medazepam in anxiety and neurasthenia; a Russian-language publication.
- 02PubMed: Semax at different stages of ischaemic stroke (2018)
the clinical study behind the stroke indication.
- 03PubMed: everything published on Selank
the whole body of work, mostly animal and cell studies.
- 04PubMed: everything published on Semax
the same view for the second peptide.
- 05ClinicalTrials.gov: search for Semax
the international trials registry: no study of the peptide is registered under the name.
- 06Russian State Register of Medicines
where the Russian registration is verified: dosage form, indications and dispensing category.
- 07WADA Prohibited List
the current list of prohibited substances and its categories.