Semax vs Selank: same tail, different parent
They share a design trick and nothing else. Both are short peptides extended with a proline-glycine-proline tail that resists peptidase cleavage. Semax comes from ACTH (4-10) and is studied for BDNF and NGF expression; Selank comes from tuftsin, an IgG fragment, and is studied for anxiolytic and neuroimmune signalling.
| Semax | Selank | |
|---|---|---|
| Parent peptide | ACTH (4-10) | Tuftsin (IgG fragment) |
| Length | 7 residues | 7 residues |
| Molecular weight | 813.9 g/mol | 751.9 g/mol |
| CAS | 80714-61-0 | 129954-34-3 |
| Studied for | BDNF and NGF expression | Anxiolytic and neuroimmune signalling |
| Stabilising tail | Pro-Gly-Pro | Pro-Gly-Pro |
What does the shared tail actually do?
Proline-glycine-proline resists peptidase cleavage, extending the half-life of a short peptide that would otherwise clear almost immediately. It is a stability modification, not a target-changing one.
Does Semax carry hormonal activity?
No. The 4-10 fragment of ACTH excludes the region responsible for corticotropic activity, which is precisely what makes it useful for separating the neurotrophic effects from the hormonal ones.
Why are they so often ordered together?
They are studied as a pair often enough that this catalogue also sells them co-lyophilized in one lot-matched vial. The single vials remain the right choice where the ratio matters.
What do the current certificates show?
Pharmacology decides which compound answers the question; the certificate decides what is actually in the vial. These are the current lots for each, read from the certificate library:
| Compound | Lot | Identity | Purity | Content | Issued |
|---|---|---|---|---|---|
| Semax | SEMX10-0803 | LC-MS/MS | 99.82% | 10.50 mg vs 10 mg label | Aug 17, 2026 |
| Selank | SEL10-0803 | LC-MS/MS | 99.83% | 10.93 mg vs 10 mg label | Aug 17, 2026 |
Purity on both lines is area percent by RP-HPLC at 214 nm, which the area-percent post explains is a ratio of peak areas and not a weight, so the two figures are comparable only because the method is the same. Content is the measured mass against the label, and the lot-to-lot post is the case for using it rather than the label in any calculation. All 114 certificates read together are in the certificate dataset.
Common questions
Is tuftsin related to ACTH?
No. Tuftsin is a four-residue fragment of the IgG heavy chain; ACTH is a pituitary hormone. The two analogues share only their stabilising tail.
Can I buy them as one vial?
Yes. The Selank and Semax blend is co-lyophilized and lot-matched. The certificate confirms each component's identity and reports its content separately; purity is a single figure for the mixture.
Where to go next
For laboratory research use only. Clinical trial results are cited as context and do not describe use of the material sold here.