Quick answer: Semax is a synthetic seven-residue peptide (Met-Glu-His-Phe-Pro-Gly-Pro) made from a four-residue fragment of ACTH with a Pro-Gly-Pro tail added to slow enzymatic breakdown. It was developed in Russia and appears in the preclinical literature on neurotrophin expression, gene-expression profiling and neurotransmitter-related markers. It is a laboratory research compound only. This explainer covers the name, structure, research themes, how it differs from Selank, and what to check on a certificate of analysis.
Where the name Semax comes from
Semax is a short trade-style name, not a sequence code, and it tells you little about the molecule behind it. The compound was developed in Russia at the Institute of Molecular Genetics of the Russian Academy of Sciences during a research program on fragments of adrenocorticotropic hormone (ACTH). In catalogs it is also written as “Semax peptide” or described by its sequence, Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP).
The peptide is a heptapeptide with a molecular weight of roughly 813 g/mol. The first four residues, Met-Glu-His-Phe, correspond to positions 4 to 7 of ACTH. The final three residues, Pro-Gly-Pro, were attached by the designers to make the fragment more resistant to enzymatic breakdown. That one design idea is the whole story of the name: a piece of ACTH, plus a protective tail.
The chemistry is covered in detail in Semax chemical structure and synthesis, and the background in the discovery and history of Semax.
Why a fragment of ACTH was used
ACTH is a 39-residue hormone, and early peptide chemists noticed that short stretches of it kept some biological activity in assays while losing the hormone’s main endocrine effect. Fragments in the region around residues 4 to 10 became a popular scaffold in neuropeptide research because they could be studied without the downstream signaling of the full-length hormone.
The trouble with any short, unprotected peptide in a biological medium is that peptidases cut it up within minutes. Adding Pro-Gly-Pro is a well-known stabilization strategy, because proline-rich ends are poor substrates for many exopeptidases. The same trick appears in the related peptide Selank, which is built on a different parent sequence. A side-by-side view is in the Selank vs. Semax comparison.
What the preclinical literature examines
Everything in this section is preclinical or mechanistic, drawn from cell and rodent work. None of it is a statement about use in people, and nothing here describes a benefit.
Neurotrophin expression. A frequently cited rat study measured brain-derived neurotrophic factor (BDNF) and its receptor TrkB in hippocampal tissue after exposure to Semax and reported changes in expression compared with controls. It is one of the most referenced papers on the compound.
Genome-wide expression profiling. Later work used transcriptional arrays in rat brain tissue and described shifts in genes connected to immune and vascular signaling in an experimental ischemia model. These are descriptive datasets that generate hypotheses rather than settle them.
Melanocortin receptor questions. Because the sequence derives from ACTH, researchers have asked whether Semax acts through melanocortin receptors. Reports describe it as lacking the corticotropic hormonal activity of the parent hormone, and the receptor picture is still discussed in the literature.
Neurotransmitter-related readouts. Some papers look at dopaminergic and serotonergic markers in animal tissue after exposure. Methods differ widely between groups.
A caution on interpretation: much of the Semax literature comes from a limited number of research groups, many of the papers are in regional journals, and independent replication is thin. Read the primary sources instead of relying on summaries. Our mechanism of action article and preclinical research summary organize them.
Semax and related compounds at a glance
Semax is often mentioned next to Selank and next to a modified form called N-acetyl Semax amidate. The table shows descriptors only, not performance.
| Compound | Length | Parent sequence | Notable feature |
|---|---|---|---|
| Semax | 7 residues (MEHFPGP) | ACTH(4-7) plus Pro-Gly-Pro | Stabilizing Pro-Gly-Pro tail |
| N-acetyl Semax amidate | 7 residues, capped ends | Semax with N-terminal acetyl and C-terminal amide | End-capping intended to slow degradation further |
| Selank | 7 residues (TKPRPGP) | Tuftsin plus Pro-Gly-Pro | Different parent; immune-related origin |
| ACTH(4-10) | 7 residues | Native ACTH fragment | No protective tail; short-lived in biological media |
The capped variant has its own page: see N-acetyl Semax amidate vs. Semax.
Handling the lyophilized powder
Semax is supplied as a freeze-dried powder. The usual rules for lyophilized peptides apply: keep sealed vials cold, dry and out of light, avoid repeated warming and cooling, and write down the date a vial is first opened. The methionine residue at the N-terminus is susceptible to oxidation over time, which is one reason air exposure and long storage after opening deserve attention. Let a cold vial reach room temperature before opening it so condensation does not form on the powder.
General notes are in Semax storage and handling.
What to check on a Semax certificate of analysis
Short peptides with a methionine and a histidine can accumulate oxidized or deletion by-products during synthesis and storage, so documentation matters more than a headline number.
HPLC purity with the chromatogram. Look for the full trace, not a single percentage, and see whether minor peaks are integrated. Understanding HPLC purity explains the numbers.
Identity confirmation. As general buying guidance, ask which method confirms a molecular weight near 813 g/mol and read it in the report. A method that only repeats the HPLC retention time says less than one that reads mass directly.
Lot reference and date that match the vial in your hands, plus the name of the testing laboratory.
Fill amount and whether it describes total powder or net peptide content.
Walk through each section with how to read a COA and Semax purity testing. For sourcing questions see where to buy Semax, and for our listing see the Semax product page.
Common misunderstandings
“Semax is just ACTH.” It contains only a four-residue stretch of ACTH plus an added tail, and reports describe it as lacking the hormone’s corticotropic activity.
“Semax and Selank are the same thing.” They share the Pro-Gly-Pro tail but come from different parent sequences and have separate literatures.
“A nasal product somewhere else defines what this vial is.” Any status or formulation a peptide has in another country does not change that products sold by V8 Peptides are for laboratory research only.
“Animal data predicts human outcomes.” It does not, and this article makes no such claim.
Frequently asked questions
What is Semax?
A synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, built from a four-residue fragment of ACTH with a Pro-Gly-Pro tail added for stability.
What does the name Semax mean?
It is a coined product-style name, not a sequence code. The sequence is written MEHFPGP.
What is Semax’s molecular weight?
Roughly 813 g/mol.
How is Semax different from ACTH?
Semax contains only residues 4 to 7 of ACTH plus Pro-Gly-Pro. Reports describe it as lacking the hormone’s corticotropic activity.
How is Semax different from Selank?
Both end in Pro-Gly-Pro, but Semax is based on ACTH and Selank on tuftsin. They are separate compounds.
What is N-acetyl Semax amidate?
A capped version with an acetylated N-terminus and an amidated C-terminus, studied as a more degradation-resistant form.
Is Semax approved in the United States?
No. V8 Peptides sells it for laboratory research use only, not for human or animal consumption.
What kind of studies mention Semax?
Rodent and cell work on neurotrophin expression, gene-expression profiling and neurotransmitter-related markers. All preclinical.
What should I look for on a Semax COA?
An HPLC chromatogram, an identity method that confirms the expected mass, a lot reference matching your vial, a test date and a named laboratory.
How is lyophilized Semax stored?
Sealed, cold, dry and protected from light, with temperature cycling avoided and the opening date recorded.
All V8 Peptides products are sold for laboratory research use only. They are not drugs, foods, or cosmetics and are not intended for human or animal consumption.
References
- Dolotov OV, et al. Semax, an analog of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Research. 2006;1117:54-60.
- Medvedeva EV, et al. The peptide semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia: genome-wide transcriptional analysis. BMC Genomics. 2014;15:228.