Guide

Semax vs selank

Two Russian heptapeptides from completely different parents. Sequences, masses, and why the acetylated amidated versions weigh more.

Published September 4, 2026

Two seven-residue peptides, both developed in Russia, both studied in neuropeptide research. That is where the similarity ends.

Peptide	Vial sizes	From
Semax	10mg	$59.99 CAD
Selank	10mg	$39.99 CAD
N-Acetyl Semax Amidate	Single size	$67.99 CAD
N-Acetyl Selank Amidate	Single size	$45.99 CAD

Free shipping across Canada. Every vial ships with a QR code linking to its own batch lab report. See all peptides

Different parents

Semax is an analog of ACTH(4-10), a fragment of adrenocorticotropic hormone, with a proline-glycine-proline tail added. Its sequence is MEHFPGP.

Selank is an analog of tuftsin, a four-residue immune peptide, with the same proline-glycine-proline tail. Its sequence is TKPRPGP.

That shared tail is why the two are often mentioned together. It is a stability modification, not a family relationship. The active part of each molecule comes from a different place and was studied for different reasons.

The numbers

	Sequence	Formula	Molecular weight	CAS
Semax	MEHFPGP	C37H51N9O10S	813.92 g/mol	80714-61-0
Selank	TKPRPGP	C33H57N11O9	751.87 g/mol	129954-34-3

Semax carries the only sulfur in either molecule, in its methionine. That shows up in the formula and it is one more thing a mass-spec result can confirm.

The acetylated, amidated versions

We carry N-acetyl semax amidate and N-acetyl selank amidate alongside the originals. The modification caps both ends of the peptide: an acetyl group on the N-terminus, an amide on the C-terminus. Peptidases attack peptides from their ends, so capping both is a stability measure. The sequence between the caps is identical to the parent.

We have not published molecular weights for these two. The identifiers are pending confirmation against a certificate of analysis for the material we stock, so the field stays blank until then. Their Specifications tabs say so.

Reconstitution

Both parents are 10 mg single-size vials.

Vial	1 mL	2 mL	3 mL	5 mL
10 mg	10 mg/mL12.3 mM	5 mg/mL6.14 mM	3.33 mg/mL4.1 mM	2 mg/mL2.46 mM

Semax vial sizes we sell, at four diluent volumes. Molarity uses 813.92 g/mol. Other volumes

Bottom line

Semax comes from ACTH, selank comes from tuftsin, and the shared tail is a stability trick rather than a family tie. Semax is 814 g/mol, selank is 752.

For research use only. Not for human or animal consumption.

Frequently asked questions

Are semax and selank related?+

Only in shape. Both are seven-residue synthetic peptides developed in Russia, but they come from different parent molecules. Semax derives from ACTH(4-10); selank derives from the immune tetrapeptide tuftsin.

What does N-acetyl amidate mean?+

An acetyl group is added to one end of the peptide and an amide to the other. Both ends are then chemically capped, which protects the sequence from the enzymes that trim peptides from their ends. The sequence in the middle is unchanged.

Do the modified versions weigh more?+

Yes, slightly. Acetylation adds about 42 g/mol and amidation changes the terminal by about 1. We do not print exact figures for our modified analogs until a certificate of analysis confirms them.

Which one is which on a lab report?+

By mass. Semax is 813.92 g/mol and selank is 751.87. Sixty grams per mole apart is unambiguous at this size.

Ready to source from Canada's most transparent peptide store?

Browse peptides