Semax is a synthetic heptapeptide derived from a fragment of adrenocorticotropic hormone (ACTH), engineered to retain central nervous system activity while removing the corticotropic action of the parent hormone. Laboratories sourcing Semax Ireland stock typically use it in rodent models examining brain-derived neurotrophic factor (BDNF) signaling, monoaminergic neurotransmission, and behavioral learning paradigms. Unlike most ACTH fragments studied historically, its structure was specifically modified for metabolic stability, which is part of why it recurs across several decades of the neuropeptide literature. It is supplied as a lyophilized powder for in-vitro and preclinical research use only, and is not authorized as a medicinal product in Ireland or the UK.

What is Semax?

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP). Its molecular formula is C37H51N9O10S, giving a molecular weight of approximately 813.9 g/mol, and it carries CAS number 80714-61-0. Structurally, it is built from two segments. The N-terminal four residues, Met-Glu-His-Phe, correspond to ACTH(4-7), the fragment of native adrenocorticotropic hormone that overlaps with the melanocortin pharmacophore shared across α-MSH and related peptides. The C-terminal tripeptide, Pro-Gly-Pro, is not part of native ACTH at all; it is a biogenic glyproline sequence appended specifically to confer resistance to plasma peptidases, since unmodified ACTH fragments are degraded within minutes in circulation.

This substitution is the defining design feature of the molecule. Native ACTH(4-10) carries an Arg-Trp-Gly tripeptide at its C-terminus, and it is that portion of the sequence, together with residues further along the full hormone, that engages the melanocortin-2 receptor responsible for corticotropic activity in the adrenal cortex. By replacing Arg-Trp-Gly with Pro-Gly-Pro, Semax retains the Met-Glu-His-Phe motif implicated in central neurotropic effects while losing meaningful MC2R engagement, so the compound does not function as a corticotropin analogue in the pharmacological sense.

Semax was developed in the Soviet Union from the 1980s onwards at what is now the Institute of Molecular Genetics of the Russian Academy of Sciences, building on earlier Soviet-era research into the behavioral effects of ACTH fragments independent of their endocrine activity. It has subsequently been registered as a prescription pharmaceutical within the Russian Federation; that registration has no bearing on its regulatory status in Ireland or the United Kingdom, where it holds no marketing authorization and is supplied only as a research chemical.

Mechanism of Action

Semax's pharmacology in the published literature is not reducible to activity at a single receptor. Several converging lines of evidence are described across the neuropeptide literature, and it is worth treating each as a distinct, separately evidenced mechanism rather than a unified pathway.

The most frequently cited mechanism concerns BDNF signaling. In rodent hippocampal and basal forebrain tissue, intranasal Semax administration has been associated with increased BDNF protein and mRNA levels, alongside changes in phosphorylation of the trkB receptor, the primary high-affinity receptor for BDNF. Because BDNF/trkB signaling is central to activity-dependent synaptic plasticity, this pathway is the one most often proposed to underlie the behavioral learning effects reported in rodent studies.

A second body of work describes effects on monoaminergic systems, reporting changes in dopaminergic and serotoninergic markers in specific rodent brain regions following Semax administration, distinct from and reported alongside the BDNF findings.

A third mechanism relates to the melanocortin system itself. Despite the removal of the C-terminal ACTH sequence responsible for MC2R activity, Semax and related ACTH(4-10) fragments have been reported to retain low-affinity interaction with central melanocortin receptor subtypes, particularly MC4R, at potency far below that of the endogenous ligand α-MSH. Additional mechanistic work has examined the peptide's interaction with enkephalin-degrading enzymes, proposing that inhibition of these enzymes prolongs endogenous opioid peptide signaling as a contributing factor in some of the neuroprotective findings.

No single receptor-binding assay fully accounts for the range of effects reported for this compound, which is part of why it remains of interest as a multi-target pharmacological tool rather than a selective ligand.

What the Research Shows

A frequently cited mechanistic study is Dolotov, Karpenko, Inozemtseva, Seredenina, Levitskaya, and colleagues, published in Brain Research in 2006. Working in adult male rats, the investigators administered Semax intranasally at 50 µg/kg body weight and measured hippocampal BDNF protein, trkB tyrosine phosphorylation, and exon III BDNF and trkB mRNA. They reported a maximal 1.4-fold increase in BDNF protein alongside a 1.6-fold increase in trkB tyrosine phosphorylation, and three-fold and two-fold increases in exon III BDNF and trkB mRNA respectively, together with improved performance in a conditioned avoidance paradigm. The full record of this hippocampal BDNF/trkB study is indexed on PubMed and is the standard primary citation for the neurotrophin pathway.

A separate line of work by Eremin, Kudrin, Saransaari, Oja, Grivennikov, Myasoedov, and Rayevsky, published in Neurochemical Research in 2005, examined Semax's effects on dopaminergic and serotoninergic systems in rodent brain tissue, reporting activation of both monoamine systems following peptide administration and situating the compound within the broader class of nootropic ACTH-derived peptides. An earlier companion paper by an overlapping author group appeared in Doklady Biological Sciences in 2004 on the same theme.

Rodent behavioral work by Yatsenko, Glazova, Inozemtseva, Andreeva, Kamensky, Grivennikov, Levitskaya, Dolotov, and Myasoedov, published in Doklady Biological Sciences in 2013, examined whether Semax attenuated the behavioral consequences of chronic unpredictable stress in rats, reporting effects on stress-related behavioral measures in that model. A related study using a neonatal maternal deprivation paradigm in rats, from an overlapping group of investigators, examined whether chronic intranasal Semax administration modified adolescent behavioral outcomes following early-life stress; findings from that line of research are further discussed in a review indexed at the National Center for Biotechnology Information, which also covers Semax's reported effects on gene expression patterns following focal cerebral ischemia in rat models.

Separately, transcriptomic work examining Semax and the Pro-Gly-Pro tripeptide in a rat model of transient middle cerebral artery occlusion has characterized changes in inflammatory and neurosignaling gene clusters in cerebral cortex tissue following peptide administration, a line of inquiry distinct from the behavioral and BDNF literature and of particular interest to researchers working on ischemia–reperfusion models.

Research Applications

In practice, the compound appears in four recurring laboratory contexts. The first is neurotrophin research, using rodent hippocampal and basal forebrain tissue to study BDNF and trkB expression and signaling as a model of activity-dependent plasticity. The second is behavioral neuroscience, using conditioned avoidance, exploratory activity, and stress-paradigm assays in rats to examine learning, anxiety-related behavior, and responses to early-life or chronic stress. The third is neurochemistry, characterizing monoaminergic (dopaminergic and serotoninergic) marker changes in discrete rodent brain regions following peptide administration. The fourth is cerebral ischemia–reperfusion research, using rodent models of focal or transient arterial occlusion together with transcriptomic and gene-expression profiling to examine downstream inflammatory and neurosignaling pathways. Certified material is also used more generally as a reference standard in analytical peptide chemistry.

Purity, Storage, and Handling

Research-grade Semax is normally specified at 98 percent or higher by reversed-phase HPLC, typically run on a C18 column with a water/acetonitrile gradient containing 0.1 percent trifluoroacetic acid. HPLC alone confirms chromatographic purity but not molecular identity, so a credible specification pairs it with mass spectrometry confirming a molecular ion near 814 Da, alongside a stated peptide content figure from amino acid analysis or nitrogen determination. Acetate or trifluoroacetate counter-ions and residual moisture both affect the true peptide-to-powder ratio, which matters directly when calculating stock solution molarity for an assay.

Batch-specific documentation is the practical safeguard here, because synthesis-related impurities — truncated sequences, incompletely coupled intermediates, residual coupling reagents — vary between production lots, and a generic or undated certificate says nothing about the specific vial being used. Laboratories comparing sources of Semax Ireland should expect a certificate of analysis tied to the actual batch number, showing the chromatogram and mass spectrum rather than a representative example, and the same standard of evidence should be applied when assessing any Best peptide company Ireland claim a supplier makes.

Lyophilized powder should be stored desiccated at −20 °C, where it remains stable over extended periods; brief ambient-temperature transit is generally tolerated but repeated freeze–thaw of the dry powder should still be avoided. Once reconstituted in bacteriostatic or sterile water, stability falls considerably, and the solution should be kept refrigerated at 2–8 °C, used within a limited window, and aliquoted at the point of reconstitution rather than repeatedly freeze–thawed. The methionine and histidine residues make the peptide susceptible to oxidative and photolytic degradation, so amber vials or foil-wrapped storage are advisable, and prepared solutions should not be left under standard laboratory lighting for extended periods.

Frequently Asked Questions

What is the difference between Semax and native ACTH(4-10)?

Semax replaces the C-terminal Arg-Trp-Gly of ACTH(4-10) with the glyproline tripeptide Pro-Gly-Pro. This confers resistance to plasma peptidase degradation and removes meaningful activity at the adrenal MC2R responsible for corticotropic effects, while the N-terminal Met-Glu-His-Phe fragment associated with central nervous system activity is retained.

Is Semax Ireland stock legal to purchase for laboratory research?

Semax is not a controlled substance in Ireland or the United Kingdom and may be supplied to research institutions and laboratories as a research chemical for in-vitro use only. It is registered as a prescription medicine in Russia, but holds no marketing authorization in Ireland or the UK, and supply for human administration here is prohibited.

What purity should a research-grade certificate of analysis show?

Expect 98 percent or higher by reversed-phase HPLC, with a mass spectrum confirming a molecular ion near 814 Da and a stated peptide content figure. The certificate should be tied to the specific batch number, showing the actual chromatogram and mass spectrum rather than a generic or undated reference document.

How stable is Semax once reconstituted?

Lyophilized powder stored desiccated at −20 °C is stable long term. In solution, stability is considerably reduced: keep refrigerated at 2–8 °C, protect from light, prepare single-use aliquots at reconstitution, and avoid repeated freeze–thaw cycles. Researchers should verify degradation kinetics under their own buffer and storage conditions.

Semax is supplied by Peptides Lab UK for in-vitro laboratory research only. It is not a medicinal product in Ireland or the United Kingdom, is not for human or veterinary use, and is not intended for diagnostic, therapeutic, or household application.