Semax vs Selank

The structural answer

Both are seven residues long. That is the end of the resemblance.

Semax is Met-Glu-His-Phe-Pro-Gly-Pro — an analogue of the ACTH(4-10) fragment, which is a fragment of adrenocorticotropic hormone. Crucially it lacks ACTH's hormonal activity: it is built from a hormone fragment without being a hormone. Molecular formula C₃₇H₅₁N₉O₁₀S, molecular weight 813.9, CAS 80714-61-0.

Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro — an analogue of tuftsin, an immunomodulatory tetrapeptide fragment of immunoglobulin G. A different parent protein entirely, from a different part of physiology.

So the comparison is between an ACTH-fragment analogue and a tuftsin analogue. They share a length and a laboratory, not a family.

Side by side

The shared Pro-Gly-Pro tail is the one real structural echo between them, and it is a design decision rather than a shared ancestry: it was appended to both to slow degradation.

What the Semax literature reports

Semax has an unusual evidence base and it is worth being precise about why. It is a registered prescription pharmaceutical in the Russian Federation, which means there is substantial Russian-language clinical literature — but little in the way of large randomised placebo-controlled trials of the kind a Western authorisation would require.

The rodent work is specific and citable. One study reported binding and increased brain-derived neurotrophic factor protein in rat basal forebrain (PMID 14556513), and a second reported BDNF and NGF gene-expression changes by brain region (PMID 19662538). Both are rat studies.

There is also a human study in stroke rehabilitation with 110 patients, published in Zhurnal Nevrologii i Psikhiatrii in 2018. It was neither randomised nor placebo-controlled, and that limitation is part of the finding rather than a footnote to it. A 110-patient uncontrolled study is not equivalent to a randomised controlled trial and we are not going to present it as one.

What we hold on Selank

Nothing — and that is the honest answer rather than an evasive one.

Selank is not in the Peptiq range, so there is no entry for it in our evidence file. We can describe its chemistry, because its sequence and its relationship to tuftsin are settled published facts. We are not going to summarise its research record, because we have not built one, and assembling a literature review for a compound we do not supply would be writing to fill a page rather than to answer the question.

Selank is not in the Peptiq range. It is described here because the comparison is asked for, and the description is limited to published chemistry and regulatory status — we do not hold an evidence file on a compound we do not supply.

Formats, and the nasal spray question

A large share of the searches that pair these two are actually about format — both are commonly offered as nasal sprays, and that is often what people are comparing.

We stock Semax as a 5mg lyophilised vial and as a ready-to-use nasal spray. The vial is reconstituted; the spray arrives in solution. The format changes the handling and nothing about the compound or its status — the same point made on the nasal sprays page, which lists everything in the range offered that way.

Supply note. Peptiq supplies research compounds for laboratory research use only. We are not a pharmacy and we do not supply licensed medicines. Where a licensed medicine is named on this page it is named to draw a distinction, not because we sell it, and nothing here is guidance on use.