What Is Semax Peptide? Structure, Mechanism, and Research

Scientifically reviewed by
Dr. Ky H. Le, MD

The information presented in this article is for educational and research purposes only, intended for laboratory professionals, researchers and collaborators. This content does not constitute medical or clinical advice.

Most ACTH-derived peptides carry significant hormonal baggage. Semax was engineered specifically to strip that away.

Developed at the Russian Academy of Sciences in the 1980s, Semax isolates the neurotrophic effects of adrenocorticotropic hormone (ACTH) while leaving its cortisol-stimulating activity behind. That design decision — a deliberate structural separation — made it one of the most studied synthetic neuropeptides in preclinical neuroscience.

This article covers what Semax is, how it’s structured, what preclinical research shows about its activity, and where in vitro investigation is currently focused.

What is Semax Peptide?

Semax is a synthetic heptapeptide with the amino acid sequence Met-Glu-His-Phe-Pro-Gly-Pro (MEHFPGP).

It is an analog of ACTH(4-10), the N-terminal fragment of adrenocorticotropic hormone. Unlike native ACTH, Semax produces no corticotropic activity — it does not stimulate cortisol secretion or interact with the adrenal axis in standard preclinical models.

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Origins and structural design

ACTH’s capacity to influence cognition and neurological function has been documented since the 1950s. Researchers at the Russian Academy of Sciences spent decades attempting to isolate those neurotrophic properties from the hormonal effects.

Semax was the result. The ACTH(4-7) fragment — Met-Glu-His-Phe — was retained for its neurotrophic activity, while the hormonal sequence was excluded. The compound was first described in scientific literature in 1991 and has since been studied across a range of preclinical neurological models.

The role of the Pro-Gly-Pro tripeptide

The PGP (Pro-Gly-Pro) sequence at Semax’s C-terminus was added to address a stability problem.

The ACTH(4-7) fragment alone degrades rapidly in serum due to peptidase activity. Adding the PGP tripeptide confers resistance to enzymatic breakdown, extending the compound’s activity window in preclinical models from roughly 15 minutes to approximately 20 to 24 hours in animal studies. Semax has a molecular weight of 813.92 Daltons and is classified as a melanocortin-related peptide.

Semax Mechanisms in Preclinical Research

Semax doesn’t appear to work through a single pathway. Preclinical research has identified at least three distinct mechanistic routes — BDNF modulation, genome-wide gene expression changes, and melanocortin receptor interactions — each investigated independently across multiple study designs.

BDNF and TrkB upregulation

The most consistently documented effect of Semax in preclinical models is its modulation of brain-derived neurotrophic factor (BDNF) and its signaling receptor, TrkB.

Dolotov et al. (2006) found that a single intranasal Semax application (50 μg/kg) produced a 1.4-fold increase in BDNF protein levels alongside a 3-fold increase in exon III BDNF mRNA in rat hippocampus, with accompanying TrkB phosphorylation. ^[1]

A related study from the same group in the Journal of Neurochemistry identified specific, calcium-dependent binding sites for Semax in rat basal forebrain tissue, with BDNF protein levels rising within 3 hours of intranasal exposure at both 50 and 250 μg/kg concentrations.^[2]

These findings suggest Semax interacts with specific binding sites in the basal forebrain — which may at least partly account for the BDNF changes observed downstream.

Genome-wide gene expression modulation

A 2014 genome-wide transcriptomics study in BMC Genomics by Medvedeva et al. examined Semax’s effect on rat brain cortex following permanent middle cerebral artery occlusion (pMCAO). Semax significantly modulated immune-response gene expression — particularly genes encoding chemokines and immunoglobulins — at both 3h and 24h post-occlusion. Twenty-four genes related to vascular function (endothelial migration, smooth muscle cell activity, vasculogenesis) also showed altered expression.^[3]

More recently, Filippenkov et al. (2024) used RNA-Seq to show that Semax compensated for ischemia-disrupted gene expression profiles in rat frontal cortex at 24 hours after transient MCAO, restoring expression of 1,171 genes associated with immune and neurosignaling pathways.^[4]

Melanocortin receptor interactions

Semax interacts with melanocortin receptors, though the precise pharmacology is still being characterized.

Available in vitro and in vivo data indicate Semax acts as a competitive antagonist or partial agonist at MC4 and MC5 receptors, without apparent interaction at MC3. Semax has also been shown to inhibit enkephalinase enzymes — proteins responsible for the degradation of endogenous regulatory peptides — at IC50 concentrations around 10 μM. This property is shared with Selank, a structurally related research peptide. For a side-by-side comparison of these compounds, see our Selank vs. Semax research overview.

Semax in Preclinical Research Models

Researchers have applied Semax across several distinct preclinical model categories, each probing different aspects of its mechanistic profile.

Cerebral ischemia and stroke models

A 2009 study by Dmitrieva et al. published in Cellular and Molecular Neurobiology examined neurotrophin mRNA expression in rat cortex following pMCAO. Semax activated transcription of BDNF, TrkC, and TrkA at 3h post-occlusion, and NGF at 24h — selectively in ischemic tissue rather than sham-operated controls.^[5]

At the protein level, Sudarkina et al. (2021) used immunodetection in a transient MCAO model to show that Semax produced upregulation of CREB (a recovery-associated protein) and downregulation of MMP-9, c-Fos, and JNK in both ipsilateral cortex and subcortical structures at 24h.^[6]

In a clinical observational study, Gusev et al. (2018) enrolled 110 post-ischemic stroke patients and reported that Semax exposure was associated with increased plasma BDNF levels throughout the observation period, with positive correlations between BDNF levels and Barthel index scores.^[7]

Chronic stress models

Inozemtseva et al. (2024) published in the European Journal of Pharmacology examined Semax in a chronic unpredictable stress (CUS) model using male Sprague-Dawley rats. Daily intraperitoneal Semax (60 nmol/kg) reversed CUS-induced anhedonia, attenuated body weight suppression, reduced adrenal hypertrophy, and restored hippocampal BDNF levels. The authors proposed that Semax’s activity at ACTH(4-10) receptors and the melanocortin system may modulate HPA axis regulation in stress conditions.^[8]

Neurodegenerative research

Semax has also been explored in optic nerve and broader neurodegenerative contexts — an area with overlap in our earlier coverage of peptides for ocular and retinal research. The peptide’s documented BDNF-elevating activity has made it a subject of interest in models where neurotrophin support is mechanistically relevant.

In vitro research applications

Research Area	Model Type	Observed Activity
BDNF/TrkB signaling	Rat hippocampus, basal forebrain	BDNF protein and mRNA upregulation
Neurotrophin gene expression	Rat ischemic cortex (pMCAO)	Activation of BDNF, NGF, TrkA, TrkC mRNA
Immune gene modulation	Rat brain cortex (focal ischemia)	Chemokine and immunoglobulin gene expression changes
Vascular gene expression	Rat brain (pMCAO)	Altered endothelial and smooth muscle gene profiles
Melanocortin receptor activity	In vitro and in vivo rat models	MC4/MC5 competitive interaction
Enkephalinase inhibition	In vitro	Degradation inhibition of endogenous regulatory peptides
Stress and anhedonia models	Rat CUS model	HPA axis marker reduction, BDNF restoration
Cerebral ischemia-reperfusion	Rat tMCAO	CREB upregulation, MMP-9/JNK downregulation

All applications are preclinical or in vitro. Semax supplied by BioLongevity Labs is for research use only.

How Semax compares to Selank

Semax shares some structural and pharmacological territory with Selank, another ACTH-related synthetic peptide.

Both are derived from the ACTH melanocortin peptide family, both inhibit enkephalinase enzymes, and both have been studied across CNS-related preclinical models. The primary divergence is mechanistic emphasis — Selank research has been oriented more toward immunomodulatory and anxiolytic pathways, while Semax research has concentrated heavily on BDNF signaling and stroke-related neuroprotection.

Sourcing Semax for in vitro research

Researchers requiring Semax for laboratory use need a supplier that documents what they’re shipping.

BioLongevity Labs provides research-grade Semax with triple third-party analytical verification from three independent certified laboratories. Each batch is confirmed by HPLC purity analysis, LC-MS molecular verification, and sterility and endotoxin testing, with COA documentation available prior to purchase.

All BioLongevity Labs peptides are manufactured in a U.S. GMP-certified facility and shipped with complete analytical documentation — a baseline requirement for protocol reproducibility. Orders placed before 12pm PT ship same-day, with free shipping on orders over $400.

Semax from BioLongevity Labs is supplied strictly for research use.

References

1. Dolotov OV, Karpenko EA, Inozemtseva LS, Seredenina TS, Levitskaya NG, Rozyczka J, et al. Semax, an analog of ACTH(4–10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Elsevier BV; 2006. https://doi.org/10.1016/j.brainres.2006.07.108
2. Dolotov OV, Karpenko EA, Seredenina TS, Inozemtseva LS, Levitskaya NG, Zolotarev YA, et al. Semax, an analogue of adrenocorticotropin (4–10), binds specifically and increases levels of brain-derived neurotrophic factor protein in rat basal forebrain. Wiley; 2006. https://doi.org/10.1111/j.1471-4159.2006.03658.x
3. Medvedeva EV, Dmitrieva VG, Povarova OV, Limborska SA, Skvortsova VI, Myasoedov NF, 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. Springer Science and Business Media LLC; 2014. https://doi.org/10.1186/1471-2164-15-228
4. Filippenkov IB, Shpetko YYu, Stavchansky VV, Denisova AE, Gubsky LV, Andreeva LA, et al. ACTH-like peptides compensate rat brain gene expression profile disrupted by ischemia a day after experimental stroke. MDPI AG; 2024. https://doi.org/10.3390/biomedicines12122830
5. 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. Springer Science and Business Media LLC; 2009. https://doi.org/10.1007/s10571-009-9432-0
6. Sudarkina OYu, Filippenkov IB, Stavchansky VV, Denisova AE, Yuzhakov VV, Sevan’kaeva LE, 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. MDPI AG; 2021. https://doi.org/10.3390/ijms22126179
7. Gusev EI, Martynov MYu, Kostenko EV, Petrova LV, Bobyreva SN. The efficacy of Semax in the treatment of patients at different stages of ischemic stroke. Media Sphere Publishing House; 2018. https://doi.org/10.17116/jnevro20181183261-68
8. Inozemtseva LS, Yatsenko KA, Glazova NY, Kamensky AA, Myasoedov NF, Levitskaya NG, et al. Antidepressant-like and antistress effects of the ACTH(4–10) synthetic analogs Semax and Melanotan II on male rats in a model of chronic unpredictable stress. Elsevier BV; 2024. https://doi.org/10.1016/j.ejphar.2024.177068