Semax is a short neuropeptide of seven amino acids. It is built from a small fragment of a natural hormone, corticotropin, with a short three-residue tail added onto the end.
Vestrand supplies it as one lot at a time, prepared for independent purity testing, with the certificate published to its verification page.
That construction is the detail worth knowing: take a short piece of a natural hormone, add a small tail, and you have Semax. The added tail is what separates it from the plain fragment it starts from, and from a closely named but differently capped substance it is sometimes confused with.
For laboratory research use only. Not for human or veterinary use.