Semax and Selank: two heptapeptides and their US status

Semax (MEHFPGP) is four residues of ACTH plus a Pro-Gly-Pro tail; Selank (TKPRPGP) is the tetrapeptide tuftsin plus the same tail. Where each came from, what the spelling variants mean, and their status as of September 2026.

By Touchstone PeptidesSeptember 22, 20266 minute read

Semax and Selank are two synthetic heptapeptides developed in Russia that share the same three-residue tail, Pro-Gly-Pro, grafted onto two different natural fragments. Semax is Met-Glu-His-Phe-Pro-Gly-Pro: residues 4 to 7 of adrenocorticotropic hormone plus the tail. Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro: the tetrapeptide tuftsin plus the tail. FDA's own briefing document describes Semax as a registered drug in Russia; neither molecule has a US approval, a US trial registration, or a place on FDA's 503A category lists.

Semax: ACTH(4-7) plus Pro-Gly-Pro

Adrenocorticotropic hormone is a 39-residue peptide cut from pro-opiomelanocortin (UniProt P01189, residues 138 to 176). Its residues 4 to 7 are Met-Glu-His-Phe; the same four residues sit at positions 4 to 7 of alpha-MSH, which comes from the same precursor. Semax keeps those four and replaces everything after them with Pro-Gly-Pro:

H-Met-Glu-His-Phe-Pro-Gly-Pro-OH (one-letter: MEHFPGP)

PubChem CID 9811102 lists it under the title "ACTH (4-7), Pro-Gly-Pro-", with formula C37H51N9O10S, average molecular weight 813.9 and CAS 80714-61-0. FDA's July 2026 briefing document gives the same formula and 813.93 g/mol and calls it "a heptapeptide and synthetic analogue of adrenocorticotropic hormone (ACTH) 4-10 fragment." The single methionine at position 1 is the residue in this sequence most exposed to oxidation; the free N-terminal amine and free C-terminal acid are unmodified.

The Pro-Gly-Pro tail comes from a separate line of Russian work on "glyprolines", short proline-glycine peptides that the same Russian school described as unusually stable; one 2003 paper from that literature describes MEHFPGP as a "hybrid peptide" built from the ACTH fragment and a glyproline. FDA's document names the same institute: the Semax used in a 2002 Russian study "was synthesized at the Laboratory of Regulatory Peptides, Institute of Molecular Genetics, Russian Academy of Sciences."

The catalog's Semax vial is listed at that sequence and molecular weight.

Selank: tuftsin plus Pro-Gly-Pro

Tuftsin is a natural tetrapeptide, Thr-Lys-Pro-Arg, with a long immunology literature of its own (reviewed in 2017); PubChem CID 156080 gives C21H40N8O6, molecular weight 500.6, CAS 9063-57-4. Selank is tuftsin with the same Pro-Gly-Pro tail Semax carries:

H-Thr-Lys-Pro-Arg-Pro-Gly-Pro-OH (one-letter: TKPRPGP)

PubChem CID 11765600 gives C33H57N11O9, average molecular weight 751.9, CAS 129954-34-3, and lists the development code TP-7 and the spelling "Selanc" among its synonyms. The sequence has no methionine, cysteine or tryptophan, so it lacks the residues that oxidize most readily; it does carry a lysine and an arginine, two basic residues that bind counter-ions, which is why an acetate salt of Selank weighs noticeably more than the free peptide and why a certificate's net peptide content matters for it. One of the Russian rat studies cited below carries the phrase "a Peptide Analog of Tuftsin" in its title, which is the lineage in one phrase.

Selank is on the catalog as a lyophilized vial, and a factory-made Selank liquid spray, a 10 mL atomized solution, is a separate format.

Two molecules, one tail

	Semax	Selank
Sequence	MEHFPGP	TKPRPGP
Natural fragment	ACTH(4-7), Met-Glu-His-Phe	tuftsin, Thr-Lys-Pro-Arg
Added tail	Pro-Gly-Pro	Pro-Gly-Pro
Formula	C37H51N9O10S	C33H57N11O9
Average MW	813.9	751.9
CAS	80714-61-0	129954-34-3
PubChem CID	9811102	11765600
Development code		TP-7
Oxidizable residues	Met1	none
Basic residues	His3	Lys2, Arg4

The shared tail is the reason the two are often sold together and written about together. It is not a reason to regard them as the same class: one descends from a pituitary hormone fragment, the other from an immunoglobulin fragment, and they share no residue outside the tail.

What "NA-Semax amidate" and the other names mean

Product names in this corner of the market are inconsistent, and they mix three layers:

Semax, Selank. The Russian names. PubChem titles the Selank record "Selank" but titles the Semax record "ACTH (4-7), Pro-Gly-Pro-" with Semax as a synonym; the spelling "Selanc" also occurs, and "TP-7" is Selank's code.
Semax acetate, Selank acetate. The salt forms. FDA's page lists the 2023 Category 2 entry for Selank as "Selank acetate (TP-7)" and evaluated Semax as both free base and acetate in July 2026, noting that it is often unclear whether the semax in the literature is the salt or the free base.
NA-Semax amidate. The name denotes an N-acetylated Semax with a C-terminal amide in place of the free acid. No PubChem record and no peer-reviewed paper under that name could be located for this article, so the exact structure of any product sold under it can only be established from that product's own certificate: sequence, modifications and an observed mass. Our catalog lists an NA-Semax amidate spray as a 10 mL atomized solution; its identity is whatever the lot certificate for that solution states, and the buffer, pH and preservative piece explains why a factory-made solution is a different product from a lyophilized vial in the first place.

What they have been studied in

Both peptides have a substantial Russian-language literature and a thin English one. For Semax, FDA's document summarizes Russian clinical studies from 1996 to 2002 alongside animal work. Selank has been studied in rats (hippocampal transcriptome after single and course exposure; a morphine-withdrawal model in outbred rats). Tuftsin itself has a long immunology literature reviewed in 2017. We list the models because that is what the literature verifiably contains; we do not summarize what the authors concluded, because a research vial carries no such conclusion.

Regulatory status as of September 21, 2026

Russia. FDA's July 2026 briefing document states that "Semax is a registered drug in Russia", citing the Russian State Register of Medicines. Whether Selank holds a Russian registration could not be confirmed from a primary source for this article, so it is not stated here as fact.

United States, Semax. No FDA-approved product; no ClinicalTrials.gov record. In Category 2 from September 29, 2023 until its nomination was withdrawn on April 22, 2026, it is now in no 503A category and not on the bulks list. FDA still took it to the Pharmacy Compounding Advisory Committee on July 24, 2026, proposing that neither Semax nor Semax acetate be placed on the list; press reported a vote in favour, FDA has published no official tally, and the recommendation is non-binding. The full timeline is in Category 1, Category 2 and the 503A bulks list. FDA's Category 2 text read:

Compounded drugs containing semax (heptapeptide) may pose risk for immunogenicity for certain routes of administration due to the potential for aggregation and peptide-related impurities.FDA, bulk drug substances page, content current April 22, 2026

United States, Selank. No FDA-approved product; no ClinicalTrials.gov record. As "Selank acetate (TP-7)" it was already outside Category 2 on FDA's page by September 27, 2024, and the April 22, 2026 page lists it as withdrawn, so it was not part of the July 2026 meeting.

WADA. Neither Semax nor Selank is named on the 2026 Prohibited List. Absence is not clearance; the list's S0 section is a catch-all for substances "with no current approval by any governmental regulatory health authority for human therapeutic use".

A vial of Semax sold here is a defined heptapeptide with a lot certificate, not the Russian registered product, and the research use only statement explains why the site publishes no use guidance for it.

Sources

For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.

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