Semax vs Selank: Research Comparison

Two short synthetic heptapeptides

Semax and Selank are synthetic heptapeptides: chains of seven amino acids designed as analogues of short regulatory peptides. They share a C-terminal Pro-Gly-Pro tripeptide, a motif added to slow breakdown by peptidases, but their first four residues come from different parent molecules.

Semax is built on ACTH(4–7), a fragment of adrenocorticotropic hormone, and is often described as an analogue of ACTH(4–10). Selank is built on tuftsin (Thr-Lys-Pro-Arg), a tetrapeptide fragment of the immunoglobulin G heavy chain. Morris Peppy lists both in 10 mg lyophilized vials.

Side-by-side reference data

Mechanisms described in the literature

Semax keeps the ACTH(4–7) core, but it is reported not to share the adrenal-stimulating hormonal activity of full-length ACTH. Rodent studies have concentrated on gene expression: transcriptome analyses after experimental cerebral ischaemia reported changes in neurotrophin, immune- and vascular-related genes. Medvedeva et al.: Semax transcriptome. Dmitrieva et al.: neurotrophin transcription.

Selank extends the tuftsin sequence. Studies have examined changes in the expression of GABA-related and other neurotransmission-related genes in rat brain tissue and in cultured cells. Volkova et al.: Selank gene expression. Gene-expression changes alone do not establish receptor binding or an effect in people.

Typical research questions

• Semax: gene expression and neurotrophin signalling in rodent models of experimental cerebral ischaemia.
• Selank: expression of GABA-related and other neurotransmission genes in rat tissue and cultured cell lines.
• Both: peptide stability, including how the Pro-Gly-Pro extension affects breakdown by peptidases.
• Clinical literature: both have limited clinical reports, mostly Russian-language publications whose abstracts do not establish randomisation, blinding or detailed safety data.

Animal and cell findings describe the model studied. They do not establish effects in people, and they are not claims about any research vial. For how to weigh this kind of evidence, see How to Evaluate Research Peptide Documentation.

Analytical considerations for short peptides

The two peptides differ by 62 g/mol (813.9 versus 751.9), so an LC-MS identity result separates them easily. For short peptides, a correct intact mass is strong evidence but not complete proof: a different arrangement of the same amino acids has the same mass. Fragmentation (MS/MS) data or comparison with a reference standard can confirm the sequence itself.

Semax’s methionine can oxidise to methionine sulfoxide, adding 16 Da. The oxidised form appears as a separate peak and mass and counts against purity. Selank’s basic residues tend to retain counterions such as acetate or trifluoroacetate. In small peptides, counterions and residual water can be a noticeable share of powder weight, which is why the measured peptide quantity is reported separately from gross powder mass. See Research Peptide Quantity Testing Explained.

How Morris Peppy tests each batch

Each Morris Peppy batch is tested by an independent U.S. laboratory. Five vials are selected at random from a single production run and put through a ten-check panel: purity (HPLC), quantity, identity, solubility, endotoxin (LAL), multi-vial conformity, fentanyl screening, container integrity, heavy metals and sterility.

Results for current batches are pending. A testing-in-progress card is not a completed result. Completed certificates of analysis are published on Lab Results before a batch is released, and each vial can be matched to its lot on Verify Product. The full process is described in how we test research peptides.

Storage and handling of lyophilized vials

Both peptides are supplied as freeze-dried powder, and the same guidance applies to unopened vials of either:

• On arrival, refrigerate unopened lyophilized vials at 2–8°C for short-term storage.
• For longer-term storage, −20°C or below is preferred.
• Keep vials sealed, away from light and moisture.
• Avoid repeated freeze–thaw cycles.
• Let a cold vial reach room temperature while still sealed before opening, to reduce condensation.

Methionine-containing peptides such as Semax are more sensitive to oxidation, which is one more reason to keep vials sealed and protected from light and moisture. These conditions apply to sealed, dry material; they are not a shelf-life claim, and this page does not cover prepared solutions.

Frequently asked questions

What is the difference between Semax and Selank?

Both are synthetic seven-amino-acid peptides ending in Pro-Gly-Pro. Semax (Met-Glu-His-Phe-Pro-Gly-Pro) is derived from the ACTH(4–7) fragment, while Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is derived from tuftsin, a fragment of immunoglobulin G.

What are the molecular formulas and weights of Semax and Selank?

Semax is C₃₇H₅₁N₉O₁₀S with a molecular weight of 813.9 g/mol. Selank is C₃₃H₅₇N₁₁O₉ with a molecular weight of 751.9 g/mol.

Are Semax and Selank approved medicines?

Both have been registered for clinical use in Russia. Neither is approved in the United States or the European Union. Morris Peppy supplies them strictly for laboratory research, not for human or veterinary use.

Why does methionine matter when testing Semax?

Methionine can oxidise to methionine sulfoxide, which adds 16 Da. LC-MS can detect the oxidised form, and it counts as an impurity in the purity result.

How should unopened vials be stored?

Refrigerate unopened lyophilized vials at 2–8°C for short-term storage. For longer-term storage, −20°C or below is preferred. Keep vials sealed, away from light and moisture, and avoid repeated freeze–thaw cycles.

Are batch test results available?

Each batch goes through up to 10 checks at independent U.S. laboratories before release. Results for current batches are pending, and completed certificates of analysis are published on the Lab Results page before a batch is released.

Related pages

• Semax product page
• Selank product page
• Lab Results: batch testing status
• Verify Product: match your lot
• How we test research peptides
• Research Peptide Quantity Testing Explained
• How to Evaluate Research Peptide Documentation