Selank Semax Blend: Two Heptapeptides in One Vial

Cover illustration: AI-generated editorial artwork. Conceptual only; not an exact molecular structure, actual laboratory result or evidence of clinical effects.

A Semax and Selank blend puts two heptapeptides of nearly identical size in one vial. They share a C-terminal Pro-Gly-Pro tail and a common origin at the Institute of Molecular Genetics in Moscow, but differ entirely in their front halves and in the research built around them. For laboratory work the blend is straightforward, with one quirk worth knowing about.

For laboratory research use only. The research materials supplied by HealthyWelness are not approved medicines, foods or cosmetics and are not for human or veterinary use. This article summarises published research and is not medical advice.

Key points

Semax (MEHFPGP, 813.9 g/mol) and Selank (TKPRPGP, 751.9 g/mol), usually 1:1 by weight.
Both end in Pro-Gly-Pro; the N-terminal halves are unrelated.
62 Da apart and oppositely charged, so easy to resolve analytically.
One fMRI study compared them side by side; none tested them together.
Only Semax contains methionine, which affects how the blend should be stored.

The two components

	Semax	Selank
Sequence	Met-Glu-His-Phe-Pro-Gly-Pro	Thr-Lys-Pro-Arg-Pro-Gly-Pro
Parent	ACTH(4-7)	Tuftsin (from immunoglobulin G)
Mass	813.9 g/mol	751.9 g/mol
Charge at pH 7	Mixed (Glu, His)	Net positive (Lys, Arg)
Oxidisable residue	Met	None
Main research theme	Neurotrophin transcription	GABA binding, enkephalinase inhibition

Individual products: Semax and Selank. Profiles: Semax and Selank. Their differences are covered in Semax vs Selank.

Why these two are paired

Three reasons appear in the literature and in practice. They were developed by the same group using the same design strategy, adding PGP to a short regulatory peptide. Their described mechanisms differ, so combining them engages more than one route. And they have been studied together: a resting-state fMRI study scanned 52 healthy participants before and 5 and 20 minutes after receiving Semax, Selank or placebo, and reported both shared and peptide-specific effects on connectivity between the right amygdala and the right temporal cortex (Panikratova et al., 2020).

That study compared the peptides; it did not administer them together. The distinction matters when a blend is described as “studied”.

The PGP question

Both peptides degrade to fragments that include PGP. Tritium-labelling work found that Semax breaks down mainly to HFPGP and PGP in the presence of nerve cells, while Selank yields TKPRP, TKP, RP and GP in plasma (Zolotarev et al., 2006). PGP is not inert: it activated neurotrophin and receptor transcription on its own in a rat ischemia model (Dmitrieva et al., 2010).

In a blend, both peptides can therefore generate the same fragment. If PGP contributes to an observed effect, a blend produces it from two sources at once, which makes attributing the effect to either parent peptide harder than it looks.

Reconstitution

Vial	Solvent	Semax	Selank	Molar ratio
10 mg (5 + 5)	1.0 mL	5 mg/mL	5 mg/mL	~1 : 1.08
10 mg (5 + 5)	2.0 mL	2.5 mg/mL	2.5 mg/mL	~1 : 1.08
20 mg (10 + 10)	2.0 mL	5 mg/mL	5 mg/mL	~1 : 1.08

Unusually for a blend, the molar ratio is close to the weight ratio here, because the two masses differ by only 8%. That makes this one of the few blends where milligram thinking does not badly mislead. Both dissolve readily in water. Use the peptide reconstitution calculator per component; method in how to reconstitute peptides.

Testing the blend

The 62 Da separation is comfortable for mass spectrometry, and the opposite charge character gives different HPLC retention: Selank’s lysine and arginine make it strongly basic, while Semax carries a glutamate. A Belgian control laboratory developed an LC-MS/MS method covering both after identifying them in seized preparations (Vanhee et al., 2020), so the analysis is well established. On a certificate, look for both masses and a ratio confirmed against standards.

One check specific to this pair: a +16 Da satellite on the Semax peak indicates methionine oxidation. Selank cannot produce that signal, so any +16 Da species in a blend belongs to Semax.

Storage

Powder at −20 °C, sealed and dark; solution at 2–8 °C.
Protect from air and light because of Semax’s methionine; Selank alone would be more forgiving.
Semax’s histidine binds copper and zinc, and acetylation alters that chemistry (Magrì et al., 2016), so avoid metal contamination in buffers.
Avoid repeated freeze–thaw; date the vial.

Selank’s described activity includes inhibiting enkephalin-degrading enzymes and modulating GABA binding (Vyunova et al., 2018), neither of which is affected by storage in the ways Semax is. In a blend, the more sensitive component sets the handling rules. See storing reconstituted peptides.

Open questions

Does co-administration produce effects that neither peptide produces alone?
Does the shared PGP fragment account for any overlap between them?
Do the two affect each other’s degradation rate in a shared solution?

Frequently asked questions

What is a Semax Selank blend?

A single vial containing both heptapeptides, usually in equal amounts. Semax is built on an ACTH fragment and Selank on tuftsin, and both end in the same Pro-Gly-Pro tripeptide.

Why are Semax and Selank combined?

They come from the same research institute, share the PGP tail, and have been studied together, including in one fMRI study comparing both against placebo. Their described mechanisms differ, which is the usual rationale for pairing peptides.

How do I calculate concentrations for the blend?

Separately for each peptide. A 10 mg vial with 5 mg of each, reconstituted with 2 mL, gives 2.5 mg/mL of each.

Can the two be told apart in a blend?

Yes. Semax is 813.9 g/mol and Selank 751.9 g/mol, a difference of about 62 Da, which mass spectrometry resolves easily. They also differ in charge, so they separate by HPLC.

Does the blend have published research behind it?

The individual peptides do, and one study compared them side by side against placebo. We found no study testing them administered together.