Educational Reference · Research-Use-Only
Semax: Mechanism, Research, and Regulatory Status
A research-grade overview of Semax — what it is, how it works at the molecular level, what published studies have shown, and answers to the questions researchers ask most.
Last reviewed 2026-07-28
What is Semax?
Semax is a synthetic melanocortin derivative consisting of the ACTH(4-7) fragment extended at the C-terminus with the tripeptide Pro-Gly-Pro, an extension generally described as conferring resistance to enzymatic degradation relative to the unmodified ACTH fragment. Radioligand studies using tritium-labelled Semax identified specific, reversible, calcium-dependent binding sites in rat basal forebrain membranes with a dissociation constant of 2.4 nM, indicating a defined binding target, though the receptor entity has not been definitively identified. A principal downstream correlate is modulation of neurotrophin signalling: Semax induces rapid, region-specific changes in Bdnf and Ngf transcription in rat hippocampus, brainstem and cerebellum.
In rodent cerebral ischemia models it activates transcription of neurotrophins and their Trk receptors selectively in ischemic cortex, whereas the effect of the Pro-Gly-Pro fragment alone is largely non-specific. Genome-wide transcriptional analysis after permanent middle cerebral artery occlusion shows that the dominant Semax-responsive gene set relates to the immune response, comprising over half of differentially expressed genes at 24 hours, with additional effects on genes governing endothelial migration and vasculogenesis. At the protein level in a transient occlusion model, Semax was associated with upregulation of active CREB in ischemic subcortical tissue and downregulation of MMP-9, c-Fos and active JNK in adjacent cortex.
The mechanistic picture is therefore best characterized as pleiotropic transcriptional modulation of neurotrophic, inflammatory and vascular gene programs rather than a single defined receptor-effector pathway.
Research highlights
What published peer-reviewed research and preclinical studies have established about Semax:
- 01Tritium-labelled Semax exhibits specific, reversible, calcium-dependent binding to rat basal forebrain membranes with a dissociation constant of 2.4 nM (Dolotov 2006).
- 02A single intranasal administration in rats produced measurable changes in Bdnf and Ngf gene expression within one hour, with direction of change differing by brain region (Agapova 2007).
- 03In the rat permanent middle cerebral artery occlusion model, immune-response genes constituted more than half of all genes whose expression was altered by Semax at 24 hours (Medvedeva 2014).
- 04Semax and its C-terminal fragment Pro-Gly-Pro both activate neurotrophin and Trk receptor transcription after cerebral ischemia, but only Semax does so selectively in ischemic tissue (Dmitrieva 2010).
- 05In a transient occlusion model, Semax administration corresponded with reduced MMP-9, c-Fos and active JNK and increased active CREB in ischemia-affected brain regions (Sudarkina 2021).
- 06Substantially all in vivo mechanistic work on Semax derives from a small number of affiliated Russian research institutions, with limited independent replication outside Russia.
Frequently asked questions about Semax
What is Semax?+
Semax is a synthetic heptapeptide, Met-Glu-His-Phe-Pro-Gly-Pro, corresponding to the ACTH(4-7) melanocortin fragment extended with a C-terminal Pro-Gly-Pro tripeptide. It is supplied as a lyophilized powder for laboratory research use only and is not approved by the FDA for any human use.
What is the proposed molecular mechanism?+
Published work describes specific nanomolar-affinity binding sites in rat basal forebrain and downstream modulation of neurotrophin (BDNF, NGF) and Trk receptor transcription, together with broad effects on immune-response and vascular gene programs in rodent cerebral ischemia models. No single receptor-effector pathway has been definitively established.
How does Semax differ from Selank?+
They share only the C-terminal Pro-Gly-Pro motif. Semax derives from ACTH(4-7) and is studied mainly in neurotrophin and ischemia-related gene expression models; Selank derives from the immunopeptide tuftsin and is studied mainly in GABAergic and enkephalin-degradation models. They are structurally and pharmacologically distinct and are not interchangeable in experimental design.
What is known about stability and reconstitution?+
As a lyophilized peptide it is hygroscopic and should be equilibrated to room temperature before opening to prevent condensation. Standard laboratory practice is reconstitution in sterile or bacteriostatic water, gentle swirling rather than vortexing to limit shear and aggregation, and aliquoting to avoid repeated freeze-thaw cycles. Note that FDA has specifically cited aggregation and peptide-related impurities as immunogenicity concerns for this substance class.
How strong is the evidence base?+
Preclinical mechanistic data are reasonably consistent but originate almost entirely from a small cluster of affiliated Russian institutions, with limited independent replication outside Russia. Human data consist of unregistered, largely non-blinded Russian clinical studies with no ClinicalTrials.gov registration. Findings should be treated as preliminary and hypothesis-generating.
References & sources
Every citation below was resolved against its primary source before publication — each PMID against the PubMed record and each DOI through doi.org. Follow any link to read the paper at the publisher rather than taking our summary on trust.
- [1]Dolotov OV, Karpenko EA, Seredenina TS, et al.. Semax, an analogue of adrenocorticotropin (4-10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain. Journal of Neurochemistry. 2006. PMID: 16805792 DOI: 10.1111/j.1471-4159.2006.03970.x
- [2]Agapova TY, Agniullin YV, Shadrina MI, et al.. Neurotrophin gene expression in rat brain under the action of Semax, an analogue of ACTH 4-10. Neuroscience Letters. 2007. PMID: 17240060 DOI: 10.1016/j.neulet.2006.12.028
- [3]Medvedeva EV, Dmitrieva VG, Povarova OV, 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. PMID: 24884442 DOI: 10.1186/1471-2164-15-228
- [4]Dmitrieva VG, Povarova OV, Skvortsova VI, Limborska SA, Myasoedov NF, Dergunova LV. Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia. Cellular and Molecular Neurobiology. 2010. PMID: 20135218 DOI: 10.1007/s10571-009-9482-3
- [5]Sudarkina OY, Filippenkov IB, Stavchansky VV, et al.. Brain protein expression profile confirms the protective effect of the ACTH(4-7)PGP peptide (Semax) in a rat model of cerebral ischemia-reperfusion. International Journal of Molecular Sciences. 2021. PMID: 34445398 DOI: 10.3390/ijms22168737
Where this data comes from
- —Citations & trial data: PubMed (NCBI, U.S. National Library of Medicine), Crossref and ClinicalTrials.gov.
- —Chemical identity: PubChem and UniProt. Where sources conflicted, the disputed value is omitted rather than guessed.
- —Regulatory status: U.S. FDA publications and, where applicable, the WADA Prohibited List. Compounding status changes frequently — verify against FDA directly before relying on it.
- —Purity, form and storage are handling and supplier conventions, not literature-derived values. Confirm against the lot-specific certificate of analysis.
Content last reviewed 2026-07-28. Compiled by Veridian Research from the primary literature. This page is an educational reference for laboratory researchers — it is not medical advice, and it describes no human use.
Regulatory status
Semax is not approved by the U.S. Food and Drug Administration for any indication and is not authorized for human use in the United States. FDA has placed Semax (heptapeptide) in Category 2 of the bulk drug substances nominated under sections 503A/503B of the FD&C Act — substances that may present significant safety risks — stating that compounded drugs containing semax may pose immunogenicity risk for certain routes of administration due to the potential for aggregation and peptide-related impurities. FDA's Pharmacy Compounding Advisory Committee reviewed Semax-related bulk drug substances in July 2026 for possible inclusion on the 503A Bulks List; advisory committee recommendations are non-binding and this status is live and may change, so verify against FDA's current published position rather than any secondary source. Semax is separately reported to be a registered medicine in the Russian Federation. Supplied strictly for in vitro and non-human laboratory research; not for human or veterinary use.
Research-Use-Only Material
Specifications and certificate of analysis
Semax is stocked as a research reagent. Analytical documentation — identity, purity and the lot-specific certificate of analysis — is published on the product record.
View specifications & COA →