Semax

Semax is a synthetic seven-amino-acid peptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro that was developed in the Soviet Union and Russia from the late 1980s onward as a modified analog of the central N-terminal fragment of adrenocorticotropic hormone (ACTH). The "Sem-" prefix in the name was chosen by the developers to evoke the conceptual lineage of the molecule from research on memory- and learning-related peptide fragments of ACTH that had been ongoing in the Soviet biomedical research community since the 1970s. The compound is one of the better-known products of the Russian neuropeptide research tradition and has been registered as a pharmaceutical product in the Russian Federation since the late 1990s, though it has not been advanced through the conventional pharmaceutical approval pathways in the United States, European Union, or other major regulatory jurisdictions.

The scientific interest in Semax sits at an unusual intersection of ACTH fragment research, neurotrophic signaling biology, and applied neuropeptide pharmacology. The N-terminal fragment ACTH(4-10) and related sequences had been studied since the 1970s for "behavioral" or "neurotrophic" activities distinct from the corticosteroidogenic activity of full ACTH that operates through the melanocortin-2 receptor on the adrenal cortex. The Russian research community, with the M. M. Shemyakin and Y. A. Ovchinnikov Institute of Bioorganic Chemistry as a central site, designed a series of modified ACTH(4-10) analogs intended to retain and extend the neurotrophic-relevant activities while improving stability and durability. Semax — with the C-terminal Pro-Gly-Pro motif replacing the natural C-terminal residues of ACTH(4-10) — emerged as one of the more characterized molecules from this design program.

The published research conversation around Semax has included reports of effects on brain-derived neurotrophic factor (BDNF) expression in various brain regions, on cholinergic system function, on cognitive endpoints in animal models, on neuroprotection in ischemia and brain injury models, and on broader behavioral and physiological endpoints in research models. The compound is registered for use as a clinical product in the Russian Federation for several neurological indications including ischemic stroke and certain cognitive disorders, with the supporting clinical-research evidence having been generated primarily within the Russian regulatory and research ecosystem. The international research-peptide market includes Semax as a tool for laboratory-research investigation of the ACTH-fragment neuropeptide family.

This page is a plain-English educational reference for readers who want to understand what Semax actually is, where it came from, what its proposed mechanisms in the published research are, and where it sits in the broader research peptide landscape. It is not a medical guide, it does not describe a treatment for any individual, and it makes no claims about cognitive or neurological effects in people who purchase the compound for laboratory use. Semax supplied as a research peptide is intended for laboratory and analytical purposes only, and the entire discussion below is framed within that context.

Throughout the page, terms that recur in Semax research — ACTH(4-10), Pro-Gly-Pro, BDNF, melanocortin receptor, nootropic — are defined as they come up, and the glossary at the end collects them. The FAQ addresses the questions that most often arise about Semax specifically and about the broader ACTH-fragment neuropeptide research conversation.

Semax is a synthetic linear heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro and a molecular mass of approximately 813 daltons in the free-acid form. The peptide has no disulfide bonds, no cyclization, and no covalent modifications beyond the standard amide-bond backbone, but its design reflects a deliberate combination of natural ACTH(4-10) residues with a modified C-terminal extension.

The first four residues — Met-Glu-His-Phe — correspond to residues 4-7 of human ACTH and are part of the conserved "core sequence" present in the N-terminal region of ACTH and of the related melanocortins (alpha-MSH, beta-MSH, gamma-MSH). The Met-Glu-His-Phe core is the canonical receptor-binding sequence of the melanocortin family and is the structural feature that allows ACTH and the MSH peptides to engage the melanocortin receptor family. The remaining three residues of Semax — Pro-Gly-Pro — are a deliberate C-terminal extension replacing the natural ACTH residues 8-10. The Pro-Gly-Pro motif is intended to confer protease resistance and improve the stability of the molecule against the proteolytic enzymes that rapidly degrade unmodified ACTH fragments.

The conceptual lineage of Semax traces to the research of Ad de Wied and colleagues in the Netherlands in the 1960s and 1970s on "behavioral" or "neurotrophic" activities of ACTH fragments distinct from the corticosteroidogenic activity of full ACTH. De Wied's group identified the ACTH(4-10) fragment as the minimum sequence retaining a number of behaviorally relevant effects in animal models, and the framework of "ACTH-like behavioral peptides" became a productive area of neuropeptide research. The Russian neuropeptide research community, building on this framework, designed modified ACTH(4-10) analogs intended to retain the behavioral and neurotrophic activities while addressing the rapid proteolytic clearance of the unmodified fragment. Semax — with its Pro-Gly-Pro C-terminal extension — emerged as a stable, well-characterized member of this design family.

The proposed mechanism of Semax in the published research is multifaceted. The melanocortin-binding core (Met-Glu-His-Phe) provides for some level of interaction with melanocortin receptors, particularly MC4R in the brain, though Semax is not a high-affinity full agonist of any melanocortin receptor in the way alpha-MSH is. The compound has also been reported to affect BDNF and other neurotrophic factor expression in various brain regions through mechanisms that are not fully resolved at the molecular level — they involve effects on transcription of the BDNF gene and on the broader neurotrophic signaling networks but the proximal molecular targets producing those effects are not as completely mapped as the melanocortin-receptor interactions. Effects on cholinergic system function, on dopaminergic and serotonergic systems, and on broader neuroinflammatory and neuroprotective pathways have all been reported in various research contexts.

It is worth being specific about what Semax is not. It is not ACTH — ACTH is the full 39-amino-acid pituitary hormone that acts on MC2R on the adrenal cortex to drive corticosteroid synthesis, and Semax is a small modified seven-amino-acid fragment-derived peptide that does not appear to engage MC2R or to drive corticosteroidogenesis in any significant way. It is not alpha-MSH or one of the natural melanocortins; while it shares the Met-Glu-His-Phe core with the melanocortin family, its modified C-terminal sequence and overall properties differ. It is not the same as Selank (another Russian neuropeptide, structurally and mechanistically distinct, with a Tuftsin lineage rather than an ACTH lineage). And it is not an approved medicine in major international regulatory jurisdictions, though it does have Russian Federation regulatory approval for several neurological indications.

The history of Semax begins with the broader history of ACTH fragment research, which dates to the 1960s. As the structure of adrenocorticotropic hormone (ACTH) was elucidated — a 39-amino-acid peptide hormone produced by the anterior pituitary that acts on the adrenal cortex to stimulate cortisol production — researchers began to ask whether different functional activities of the molecule could be assigned to different regions of the sequence. The corticosteroidogenic activity (the canonical adrenal-stimulating function) was traced to engagement of MC2R, the melanocortin-2 receptor, by the N-terminal region of ACTH including the Met-Glu-His-Phe-Arg-Trp(MEHFRW) "core sequence" present across the melanocortin family.

In parallel with the corticosteroidogenic biology, work in the 1960s and 1970s — particularly by Ad de Wied and collaborators at the Rudolf Magnus Institute in Utrecht — identified behavioral and neurotrophic activities of ACTH and its fragments that were distinct from the corticosteroidogenic activity. The ACTH(4-10) fragment specifically was identified as the minimum sequence retaining a number of these "extra-adrenal" activities in animal models, including effects on memory, on attention, and on behavioral arousal. This work established the conceptual framework of "neurotrophic ACTH fragments" — peptides derived from the N-terminal region of ACTH that retained behavioral relevance but operated through mechanisms distinct from the adrenal axis.

The natural ACTH(4-10) fragment, however, is rapidly degraded by aminopeptidases and other proteases, with a very short biological half-life. To develop more stable analogs suitable for systematic research and possible clinical application, researchers in several laboratories pursued modification strategies — including amino acid substitutions, C-terminal extensions, and conformational constraints. The Russian neuropeptide research community, with the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry as a central site, developed a series of modified ACTH(4-10) analogs through the 1980s. Semax — with the modified Met-Glu-His-Phe-Pro-Gly-Pro sequence — was identified within this design effort as a stable, well-characterized analog suitable for further investigation.

Through the 1990s, Semax was advanced through laboratory and clinical-research studies in the Soviet Union and Russia. The research focused on cognitive endpoints, on neuroprotection in ischemia and brain injury models, on the BDNF expression effects in various brain regions, and on the broader neurotrophic and behavioral effects characteristic of the ACTH-fragment family. The compound was registered as a pharmaceutical product in the Russian Federation in the late 1990s for use in ischemic stroke and certain cognitive disorders, with the registration based on Russian clinical-research evidence within the Russian regulatory framework. The Russian product is supplied as an intranasal solution, reflecting the development pathway in that regulatory context.

The international scientific community has engaged with the Semax literature at various points, with English-language publications appearing in mainstream neuroscience and peptide journals through the 2000s and 2010s. The international engagement has been substantive but has not produced corresponding regulatory approvals in major jurisdictions outside Russia. Independent replication of some of the key findings — particularly the BDNF expression effects and the neuroprotection findings — has occurred to some degree but remains less comprehensive than for compounds with broader international development histories.

Important milestones in the Semax literature include the de Wied work establishing the behavioral framework for ACTH fragments in the 1960s-1970s, the design and characterization of Semax by the Russian neuropeptide research community in the 1980s, the clinical-research and registration of Semax as a Russian pharmaceutical product in the 1990s, the BDNF expression and neuroprotection research expansion in the 2000s, and the continuing presence of the compound in the international research-peptide market and the international neuropeptide research literature.

The science of Semax is anchored in three connected areas: ACTH and melanocortin biology, the broader landscape of neurotrophic and "behavioral" peptides derived from ACTH fragments, and the specific cellular and molecular pharmacology of Semax characterized in the published research.

• Semax is a synthetic seven-amino-acid peptide developed as a stabilized analog of ACTH(4-10).
• The Met-Glu-His-Phe core retains some melanocortin-receptor interaction; the Pro-Gly-Pro extension confers protease resistance.
• Published research includes effects on BDNF expression, cholinergic function, and neuroprotection in ischemia models.
• Registered as a pharmaceutical product in the Russian Federation for ischemic stroke and certain cognitive indications.
• Not approved in the U.S., EU, or other major regulatory jurisdictions; available internationally as a research peptide.

Structurally, Semax is a linear heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro and a molecular mass of approximately 813 daltons in the free-acid form. The peptide has no disulfide bonds and no cyclization, and the only "design modifications" relative to the natural ACTH sequence are the C-terminal residues 5-7 of the Semax sequence (Pro-Gly-Pro) replacing the natural ACTH residues 8-10 (Arg-Trp-Gly).

The first four residues of Semax — Met-Glu-His-Phe — are identical to residues 4-7 of human ACTH and represent the canonical melanocortin "core sequence" present across the melanocortin peptide family (ACTH, alpha-MSH, beta-MSH, gamma-MSH). This core sequence is the principal contact region for binding to the melanocortin receptors and is essential for any melanocortin-receptor activity. The Met at position 1 (corresponding to ACTH residue 4) is subject to oxidation under air exposure, and oxidized methionine-containing Semax may have altered properties.

The C-terminal Pro-Gly-Pro motif is the distinctive design feature of Semax. Proline residues are conformationally restricted because of the imino acid ring structure, and proline-containing sequences tend to be more resistant to proteolytic degradation than analogous sequences with other residues. The Pro-Gly-Pro motif specifically combines two prolines with an intervening glycine in a configuration that confers substantial resistance to the aminopeptidases and other proteases that would otherwise rapidly degrade the C-terminal end of an ACTH-fragment analog. The design rationale was to retain the receptor-binding-relevant N-terminal core while providing C-terminal stability sufficient for a usable biological half-life and for sufficient CNS exposure when administered intranasally.

The histidine at position 3 (corresponding to ACTH residue 6) is a critical residue for the melanocortin core sequence's receptor binding. The phenylalanine at position 4 (corresponding to ACTH residue 7) is also a critical receptor-binding residue. The Met at position 1 and the Glu at position 2 contribute to the overall properties of the core sequence and to its interactions with the receptor binding pocket.

Stability characteristics of Semax are favorable enough for practical research use. The Pro-Gly-Pro C-terminus provides significantly better protease resistance than the natural ACTH(4-10) sequence. Lyophilized material stored sealed at deep-freeze temperatures away from light is generally considered stable for extended periods. The methionine at position 1 requires care with oxidation, and standard practice includes storage under inert atmosphere where possible and avoidance of air exposure of reconstituted material.

Research-grade Semax is produced through standard solid-phase peptide synthesis using Fmoc protecting-group chemistry, with the proline-containing C-terminus requiring some attention to coupling efficiency at the difficult Pro-Pro junctions. The crude peptide is purified by reversed-phase HPLC and characterized by mass spectrometry. A Certificate of Analysis for research-grade Semax typically reports the sequence, the measured molecular mass, the HPLC purity percentage, and the residual moisture content of the lyophilized powder.

Semax has been used as a research tool across a focused set of themes connected to ACTH-fragment biology, neurotrophic signaling, cognitive and behavioral neuroscience, and neuroprotection. None of the areas described below represents a therapeutic use of Semax in individuals outside the Russian regulatory framework, and none should be read as suggesting clinical benefit in other contexts. They are research directions where the compound has been useful as a defined experimental probe.

• BDNF expression and neurotrophic signaling research
• Cognitive and behavioral neuroscience studies
• Neuroprotection research in ischemia and brain injury models
• Cholinergic system function research
• Melanocortin receptor pharmacology in the CNS context
• Intranasal peptide delivery research
• Comparative ACTH-fragment research

Semax sits in a family of ACTH-fragment-derived peptides and Russian neuropeptides, and is best understood relative to several distinct categories of compound.

The closest comparison is with natural ACTH(4-10) — the Met-Glu-His-Phe-Arg-Trp-Gly sequence that represents the original "behavioral fragment" identified by de Wied and others. Natural ACTH(4-10) has substantial behavioral and neurotrophic activity in research models but is rapidly degraded with a very short biological half-life. Semax shares the N-terminal Met-Glu-His-Phe core with ACTH(4-10) but substitutes the modified Pro-Gly-Pro C-terminus to confer protease resistance. The comparison illustrates the design trade-offs between fidelity to the natural sequence and stability for research and clinical use.

A second comparison is with the natural melanocortins — alpha-MSH (an octapeptide), beta-MSH (a tetrapeptide hormone in newer nomenclature though originally described as longer), and gamma-MSH. These compounds share the Met-Glu-His-Phe-Arg-Trp core sequence with ACTH and engage the melanocortin receptors with relatively high affinity. Semax is a much lower-affinity, partial-agonist or modulator-like compound at the melanocortin receptors compared to these natural full agonists.

Semax is also compared with Selank, the other prominent Russian neuropeptide. Selank is structurally and mechanistically distinct from Semax — it derives from the Tuftsin tetrapeptide (Thr-Lys-Pro-Arg) rather than from ACTH, has a different proposed mechanism involving GABAergic and other systems, and is registered in Russia for different indications. The two compounds are often discussed together because of their shared Russian research lineage but should not be conflated as alternative versions of the same compound.

In the international research peptide market and the broader cognitive/nootropic peptide conversation, Semax is sometimes grouped with other peptides studied in cognitive contexts including Cerebrolysin (a heterogeneous brain-extract preparation), Noopept (a small molecule, not a peptide despite the name), and various GHRH/GHRP combinations. These compounds have entirely different research lineages and proposed mechanisms; Semax's specific identity as a stabilized ACTH(4-10) analog distinguishes it within this broader cognitive-research conversation.

The Semax literature gives a particular impression: a stable, well-characterized synthetic analog of the natural ACTH(4-10) "behavioral fragment," developed in the Russian neuropeptide research community in the 1980s, advanced through Russian clinical-research and registered as a pharmaceutical product for ischemic stroke and certain cognitive indications in the Russian Federation, and present in the broader international research-peptide market and the international neuropeptide research literature as a tool for laboratory-research investigation of ACTH-fragment biology and neurotrophic signaling. The compound's place in the broader peptide research landscape is distinctive: it carries the conceptual lineage of the de Wied behavioral-fragment framework into a usable stabilized form, with a substantial Russian clinical-research evidence base supporting the local regulatory approval and an ongoing international research literature exploring the molecular mechanisms.

The conceptual foundation of Semax is reasonably well grounded. The ACTH(4-10) behavioral-fragment framework has substantial supporting research from the 1960s-1970s and continues to be a productive area of neuropeptide research. The design rationale for Semax — retain the receptor-binding core, modify the C-terminus for stability — is a clear and well-executed example of peptide medicinal chemistry. The compound's effects on BDNF expression, on cholinergic function, and on neuroprotection in animal-model contexts have substantial supporting research, though the detailed proximal molecular targets of the BDNF and other transcriptional effects are not fully resolved.

The clinical-research arc of Semax is substantive but largely confined to the Russian regulatory environment. The compound is registered in the Russian Federation for ischemic stroke and certain cognitive indications, with supporting clinical-research evidence generated primarily within the Russian research and regulatory ecosystem. The compound has not been advanced through the conventional pharmaceutical approval pathways in the U.S., EU, or other major international regulatory jurisdictions, and the international scientific community's engagement with the clinical-research literature has been at a level somewhat below the engagement with comparable compounds that had broader international development histories.

Independent replication and characterization of Semax findings outside the Russian research community has occurred to a meaningful degree but is less comprehensive than for many compounds with broader international development. The intranasal pharmacokinetics, the BDNF expression effects, the neuroprotection findings, and the cognitive endpoint findings have all been examined by international research groups at various points, with the overall picture broadly supporting the Russian findings while leaving various detailed mechanistic questions open.

Methodologically, Semax research has used cell-culture systems, animal models (rodent learning, memory, ischemia, and brain injury models predominantly), and human clinical-research studies in the Russian regulatory context. The pharmacokinetic profile is characterized to a reasonable degree of detail, particularly for the intranasal route used in the Russian product. The pharmacodynamic profile across the various research endpoints has been documented but with the limitations that the relatively concentrated Russian research community brings.

Open questions in the Semax field include the proximal molecular targets responsible for the BDNF transcriptional effects, the relative contributions of melanocortin-receptor signaling versus melanocortin-receptor-independent pathways to the various behavioral and neuroprotective effects, the comparative biology with other modified ACTH-fragment analogs, and the translation of Russian clinical-research findings to controlled-study contexts in other regulatory environments.

For students, researchers, and curious readers approaching Semax for the first time, the most accurate framing is that of a thoughtfully designed stabilized ACTH-fragment analog with a substantial research literature anchored in the Russian neuropeptide research community, with effects on neurotrophic signaling and neuroprotection in animal-model contexts, and with a Russian Federation pharmaceutical registration that does not extend to other major regulatory jurisdictions. The compound is supplied for laboratory and analytical use only as a research peptide in the international market, and educational discussion of it needs to stay within that framing rather than drift into therapeutic recommendations or claims about effects in people who purchase the compound for research.

Semax is a synthetic seven-amino-acid peptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, developed in the Russian neuropeptide research community as a stabilized analog of the natural ACTH(4-10) "behavioral fragment" of adrenocorticotropic hormone. The first four residues preserve the canonical melanocortin core sequence of ACTH; the C-terminal Pro-Gly-Pro extension confers protease resistance and improves stability relative to the unmodified fragment.

The published Semax research literature includes effects on brain-derived neurotrophic factor (BDNF) expression in various brain regions, effects on cholinergic system function, effects on cognitive endpoints in animal models, and effects on neuroprotection in ischemia and brain injury models. The compound is registered as a pharmaceutical product in the Russian Federation for ischemic stroke and certain cognitive indications, with supporting clinical-research evidence generated primarily within the Russian regulatory and research ecosystem. It has not been advanced through the conventional pharmaceutical approval pathways in the U.S., EU, or other major international jurisdictions and is available internationally as a research peptide for laboratory and analytical use.

This page treats Semax as an educational subject and a research peptide. It is supplied for laboratory and analytical use only. Nothing in the discussion above constitutes medical advice, describes a treatment for any individual outside the Russian regulatory framework, or makes claims about cognitive or neuroprotective effects in people who purchase the compound for research. The framing throughout reflects the compound's actual status: a thoughtfully designed stabilized ACTH-fragment analog with a substantial Russian research literature, registered as a pharmaceutical product in one regulatory jurisdiction, and present internationally as a research peptide of laboratory interest with a continuing role in basic investigation of ACTH-fragment biology and neurotrophic signaling.