What it is
N-acetyl semax amidate is semax with both ends capped. Semax is a seven-amino-acid peptide — Met-Glu-His-Phe-Pro-Gly-Pro, a fragment of the hormone ACTH with a stabilising tail — that is a registered medicine in Russia. The variant sold as N-acetyl semax amidate adds two small chemical groups:
- an acetyl cap on the front (N-terminal) end, and
- an amide on the back (C-terminal) end.
Both are standard tricks in peptide chemistry. The enzymes that break peptides down often start at the ends, and capping the ends is a common way to slow them. PubChem records the result as C39H54N10O10S, molecular weight 855.0, against semax's C37H51N9O10S, 813.9. That is a different molecule — which matters, because everything known about semax was learned from semax.
Where the name comes from
The chemical record tells its own story. PubChem created its entry for N-acetyl semax amidate (CID 172638603) on 31 December 2024. On 23 September 2026 the sources deposited on that record were nine chemical suppliers — peptide catalogues and screening-compound vendors — and no journal and no patent.
Compare semax, whose PubChem record sits beside 200-plus PubMed papers. This variant's record sits beside a supply chain.
What the literature holds under the name: nothing
A PubMed search for "N-acetyl semax" OR "N-acetyl-semax" OR "semax amidate" appears to return six papers. It does not. PubMed silently rewrites a quoted phrase it does not recognise into loose words, and its own response carries a warning list that, in this case, names all three phrases as not found. The true count of papers using the name is zero.
Searched more loosely — semax with any acetyl term — seven records come back. Two of them actually study an acetylated semax. Neither tests the form that is sold.
The two papers that come closest
A 2016 cell study (Journal of Inorganic Biochemistry) compared semax with Ac-Semax, semax carrying only the front-end acetyl cap. Acetylation changed how the peptide binds copper, and in neuroblastoma cells exposed to copper, Ac-Semax did not protect them — semax did. The authors called the free front end "crucial" to that protection. It is a single cell study of one effect, but it is the only direct comparison found, and it points the opposite way from the sales claim.
A 2013 paper (Doklady Biological Sciences) studied the stability of acetylated semax to breakdown in various biological media. That is the kind of result the "longer-lasting" claim leans on — and it concerns the acetyl-only form, in the laboratory, with no measure of effect.
So the honest summary is short: capping the ends may slow breakdown, and in the one test of function, one of the two caps removed a protective effect. No study has looked at the double-capped molecule at all.
Where it stands
Not approved anywhere; the registered medicine in Russia is semax itself. Drugs@FDA returned nothing on 2026-09-23. In a 2021 warning letter, FDA stated that semax was not nominated for the 503A bulks list, the list of substances that may lawfully be compounded in the United States.
Related reading
Semax for the parent medicine and its Russian clinical record, and selank, the other short Russian peptide medicine that research-chemical suppliers sell beside it. For the wider category, see peptides for focus and mood.