Semax

1. Overview

Semax is a synthetic heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, corresponding to the ACTH(4-7) fragment with an added C-terminal Pro-Gly-Pro tripeptide designed to improve metabolic stability [6]. It was developed in the 1980s at the Institute of Molecular Genetics of the Russian Academy of Sciences under the direction of Nikolai Myasoedov and Igor Ashmarin.

In Russia, semax is approved as a pharmaceutical product and is available as a 0.1% and 1% intranasal solution. Approved indications in Russia include treatment of acute ischemic stroke, cognitive disorders of various origin, and peptic ulcer disease [6]. Outside of Russia, semax has no regulatory approval and remains classified as a research compound.

Molecular Weight

813.93 g/mol

Sequence

Met-Glu-His-Phe-Pro-Gly-Pro

Half-life

Several minutes in plasma; active metabolites may persist longer

Routes Studied

Intranasal (primary), intravenous

FDA Status

Not approved outside Russia

WADA Status

Not specifically listed

2. Mechanism of Action

Semax exerts its effects through several proposed mechanisms, though the relative contribution of each pathway remains under investigation.

BDNF and Neurotrophic Factor Upregulation

The most consistently reported mechanism involves upregulation of brain-derived neurotrophic factor (BDNF). Intranasal administration of semax in rats produced a rapid increase in BDNF mRNA expression in the hippocampus and basal forebrain [1] [5]. Semax also increases expression of nerve growth factor (NGF) and the TrkB receptor, which mediates BDNF signaling [5] [8].

Melanocortin System Interaction

As a derivative of ACTH(4-10), semax interacts with melanocortin receptors, though it lacks the steroidogenic activity of full-length ACTH. The melanocortin system is involved in learning, memory, attention, and stress responses [6]. Unlike ACTH, semax does not stimulate adrenal cortisol secretion at therapeutic doses.

Monoaminergic Effects

Semax modulates dopaminergic and serotonergic neurotransmission. Studies in rodents demonstrated increased dopamine and serotonin turnover in the striatum and nucleus accumbens following intranasal administration [1].

Enkephalinase Inhibition

The C-terminal Pro-Gly-Pro motif of semax acts as a substrate and inhibitor of enkephalin-degrading enzymes (enkephalinases), which may prolong the action of endogenous opioid peptides and contribute to analgesic and neuroprotective effects [6].

3. Researched Applications

Cognitive Enhancement

In a placebo-controlled study in healthy human volunteers, a single intranasal dose of semax improved performance on attention and short-term memory tasks [4]. Animal studies have consistently shown improved learning and memory in maze and passive avoidance paradigms [6]. The cognitive effects are thought to be mediated through BDNF-dependent synaptic plasticity.

Stroke Recovery

The most robust clinical evidence for semax comes from Russian trials in acute ischemic stroke. In a randomized trial of 100 patients, intranasal semax at 12 mg/day for 5 days accelerated neurological recovery compared to standard care [3]. Animal models of cerebral ischemia have demonstrated that semax reduces hippocampal neuronal death and activates transcription of neurotrophic factors following ischemic injury [2] [8].

Neuroprotection

Beyond stroke, semax has shown neuroprotective effects in various animal models of neuronal injury. It reduces oxidative stress markers, attenuates glutamate excitotoxicity, and promotes neuronal survival in models of incomplete global ischemia [2]. These effects are attributed to the combined neurotrophic and anti-inflammatory actions of the peptide.

Spinal Cord Injury (2025)

Liu et al. (2025) demonstrated in a preclinical study that semax promoted functional recovery after spinal cord injury (SCI) in female mice [12]. RNA sequencing revealed that semax regulated the ubiquitin-specific protease USP18. Network pharmacology and molecular docking identified the mu opioid receptor (Oprm1) as a key semax target. The peptide inhibited lysosomal membrane permeabilization (LMP)-related pyroptosis and reduced oxidative stress and neuroinflammation, promoting SCI recovery through a mu opioid receptor/USP18/FTO deubiquitination pathway. This study identified a novel mechanism of action for semax distinct from its established melanocortin and neurotrophic pathways.

Alzheimer's Disease (2025)

A 2025 study evaluated semax and a modified derivative in a murine Alzheimer's disease model [13]. Both peptides improved cognitive functions across multiple behavioral tests. Histological examination showed reduced amyloid inclusions in the cortex and hippocampus. These findings add to semax's growing evidence base for neurodegenerative disease applications and demonstrate high potential for developing therapeutic strategies targeting Alzheimer's pathology.

Attention Deficit Hyperactivity Disorder (ADHD)

Preliminary Russian clinical reports have described improvements in attention and behavioral measures in children with ADHD treated with intranasal semax, though well-controlled clinical trial data for this indication are limited [7].

4. Pharmacokinetics

Intranasal Absorption and BBB Penetration

Semax is administered exclusively via the intranasal route, which exploits the olfactory and trigeminal nerve pathways to bypass the blood-brain barrier (BBB). Animal studies using radiolabeled semax have demonstrated detectable peptide levels in brain tissue within 1-3 minutes of intranasal application [10]. The intranasal bioavailability is estimated at approximately 60-70% relative to intravenous administration, which is exceptionally high for a peptide compound. Direct evidence of BBB penetration comes from studies showing rapid increases in BDNF mRNA expression in deep brain structures (hippocampus, basal forebrain) within 20-30 minutes of intranasal dosing, consistent with direct central nervous system access rather than a peripherally mediated mechanism [1] [5].

Half-Life and Metabolism

The plasma half-life of intact semax is very short, on the order of 2-3 minutes, reflecting rapid enzymatic degradation by serum carboxypeptidases, aminopeptidases, and other plasma proteases [10] [6]. However, the pharmacological duration of action substantially exceeds the plasma half-life. This discrepancy is explained by two factors: rapid tissue distribution into the CNS compartment where enzymatic degradation is slower, and the generation of active metabolites (including the Pro-Gly-Pro tripeptide and ACTH(4-7) fragments) that retain biological activity.

The Pro-Gly-Pro Stability Extension

The C-terminal Pro-Gly-Pro tripeptide represents a deliberate pharmacological design choice that distinguishes semax from native ACTH(4-7) (Met-Glu-His-Phe). Unmodified ACTH(4-7) has a plasma half-life of under 30 seconds due to rapid carboxypeptidase cleavage. The Pro-Gly-Pro extension confers approximately 10-fold greater enzymatic stability by creating a proline-rich C-terminus that resists carboxypeptidase degradation [6] [10]. Additionally, the Pro-Gly-Pro fragment itself possesses independent biological activity, including anti-inflammatory properties and the ability to stimulate neurotrophic factor expression [8]. This means the metabolic breakdown of semax generates bioactive fragments rather than inactive products, effectively extending the pharmacological window beyond what the parent compound half-life would suggest.

5. Clinical Evidence

Clinical trial data for semax comes almost exclusively from Russian publications. The stroke recovery trial by Gusev et al. represents the most methodologically rigorous published study, demonstrating benefit of high-dose intranasal semax in acute ischemic stroke [3]. The cognitive enhancement study by Kaplan et al. showed acute effects on attention in healthy volunteers [4].

It should be noted that these trials were generally conducted before the widespread adoption of international trial reporting standards (CONSORT, etc.), and many are available only in Russian-language journals. Independent replication of the clinical findings by non-Russian research groups has not been published. No trials registered on ClinicalTrials.gov or equivalent Western trial registries have been identified.

6. Dose-Response Relationships

Nootropic Dose Range

The nootropic (cognitive-enhancing) dose range for semax is 50-600 mcg per administration via the intranasal route, typically delivered 2-3 times daily. The Russian 0.1% formulation delivers approximately 50 mcg per drop, with standard nootropic dosing at 3-6 drops per nostril per session [6]. At these doses, the primary pharmacological effects include enhanced attention, improved working memory, and increased processing speed, with onset occurring within 15-30 minutes and noticeable effects lasting 4-8 hours despite the short plasma half-life [4]. The rapid onset is consistent with direct neurotransmitter modulation (dopaminergic and serotonergic turnover), while sustained effects over hours reflect the slower neurotrophic factor upregulation cascade.

Neuroprotective Dose Range

Neuroprotective applications employ substantially higher doses. The stroke trial by Gusev et al. used 12 mg/day (12,000 mcg), approximately 20-fold higher than standard nootropic doses [3]. The Russian 1% formulation (approximately 500 mcg per drop) is specifically designated for these clinical scenarios. At higher doses, semax activates broader gene expression programs including anti-apoptotic pathways, inflammatory modulation, and vascular remodeling genes [8] [11].

Gene Expression Changes Across Doses

Genome-wide transcriptome analysis has revealed that semax produces dose-dependent changes in gene expression, with over 100 genes significantly affected in rat brain tissue [9]. At lower (nootropic-range) doses, the predominant changes involve immediate-early genes associated with synaptic plasticity (Fos, Egr1, Arc) and neurotransmitter receptor expression. At higher (neuroprotective-range) doses, additional gene clusters are recruited, including those involved in immune modulation, angiogenesis, and neuronal survival pathways [9] [11]. This dose-dependent gene expression profile supports the concept that nootropic and neuroprotective effects represent a continuum rather than separate mechanisms.

Onset, Duration, and Timing

Subjective cognitive effects are typically reported within 15-30 minutes of intranasal administration at nootropic doses. Neurotrophic factor upregulation (BDNF, NGF) begins within 20-30 minutes and peaks at 1.5-3 hours [1] [5]. Gene expression changes peak at 3-6 hours and some persist for 24 hours following a single dose [9]. For nootropic purposes, the Russian prescribing information recommends courses of 3-14 days, suggesting cumulative neurotrophic effects that build over repeated dosing. Extended courses beyond 14 days have not been systematically studied.

7. Dosing in Published Research

The following doses have been used in published research. These are not recommendations and should not be interpreted as therapeutic guidance.

The commercially available Russian formulation (Semax 0.1%) delivers approximately 50 mcg per drop. The 1% formulation is prescribed for more severe neurological conditions and delivers approximately 500 mcg per drop [6].

8. Comparative Effectiveness

Semax vs Selank

Semax and Selank are both Russian-developed intranasal heptapeptides, but they target different pharmacological pathways and are considered complementary rather than competing agents. Semax is derived from ACTH(4-10) and primarily modulates the melanocortin system, dopaminergic/serotonergic neurotransmission, and BDNF expression, producing predominantly nootropic and neuroprotective effects. Selank is derived from the endogenous tetrapeptide tuftsin and primarily modulates the GABAergic system and enkephalin metabolism, producing predominantly anxiolytic and immunomodulatory effects. In Russian clinical practice, the two peptides are sometimes used concurrently (semax for cognitive enhancement, selank for anxiety reduction) based on the rationale that their mechanisms do not overlap. No head-to-head clinical trials comparing the two have been published, but they share the advantages of intranasal delivery, short plasma half-life, and favorable safety profiles.

Semax vs Piracetam and Classical Nootropics

Compared to piracetam and other racetam-class nootropics, semax acts through a fundamentally different mechanism. Racetams primarily modulate AMPA and acetylcholine receptors with relatively subtle cognitive effects. Semax operates through neurotrophic factor upregulation (BDNF, NGF), melanocortin receptor activation, and monoaminergic modulation, representing a broader spectrum of neurobiological activity [1] [5] [6]. Animal comparison studies suggest semax produces more robust effects on memory consolidation than piracetam, particularly in models of cognitive impairment rather than baseline enhancement. However, direct clinical comparison data in humans are lacking.

N-Acetyl Semax and N-Acetyl Semax Amidate

Two modified versions of semax are available through research chemical suppliers: N-Acetyl Semax (NASA) and N-Acetyl Semax Amidate (NASA-Amidate). N-Acetyl Semax features an acetyl group on the N-terminal methionine, which reduces aminopeptidase degradation and is reported to increase the effective half-life by 2-3 fold compared to unmodified semax. N-Acetyl Semax Amidate adds both the N-terminal acetylation and a C-terminal amidation, providing resistance to both amino- and carboxypeptidases. Users in the nootropic community generally report that these modifications produce stronger and longer-lasting cognitive effects per dose, though no peer-reviewed clinical or pharmacokinetic studies have been published on either modified variant. The Russian regulatory approval and all published clinical data apply exclusively to unmodified semax.

Semax vs ACTH Fragment Drugs

Several ACTH-derived peptide drugs exist besides semax, including Org 2766 (an ACTH(4-9) analogue studied in Europe) and ebiratide (an ACTH(4-9) analogue studied in Japan). Semax differs from these compounds in its specific sequence extension (Pro-Gly-Pro), which provides both enhanced stability and independent pharmacological activity through enkephalinase inhibition [6]. Org 2766 reached Phase II/III trials for diabetic neuropathy and showed some cognitive effects but was ultimately discontinued. Semax is the only ACTH-fragment peptide drug that achieved full regulatory approval (in Russia) for both cognitive and neurological indications, though direct comparative efficacy data between these compounds are not available.

9. Safety and Side Effects

Published Russian clinical data report a generally favorable safety profile. Commonly reported side effects include mild nasal irritation at the application site. No significant adverse effects on blood pressure, heart rate, cortisol levels, or hematological parameters have been reported in clinical studies [3] [6].

Notably, semax lacks the steroidogenic and adrenal-stimulatory effects of full-length ACTH, which is attributed to the truncated sequence retaining only the neurotrophic-active fragment [6].

Long-term safety data are limited. The Russian prescribing information recommends treatment courses of 3-14 days with intervals between courses. Safety in pregnancy, pediatric populations (outside of limited ADHD reports), and patients with significant renal or hepatic impairment has not been systematically studied.

10. Enhanced Safety Profile

Russian Clinical and Regulatory Safety Data

Semax has been in clinical use in Russia since its approval in the mid-1990s, providing over two decades of post-marketing pharmacovigilance data. The Russian Phase III clinical program included studies in acute ischemic stroke (doses up to 12 mg/day), cognitive disorders, and optic nerve diseases [3] [6]. Across these trials, semax consistently demonstrated a safety profile comparable to placebo, with the only commonly reported adverse effect being transient mild nasal mucosal irritation at the administration site. No clinically significant changes in vital signs, laboratory parameters, or ECG findings were attributed to semax in any published clinical trial [3] [6] [11].

Absence of Dependency and Tolerance

Unlike stimulant-based cognitive enhancers (amphetamines, methylphenidate, modafinil), semax does not act through catecholamine reuptake inhibition or direct dopamine receptor agonism. Its dopaminergic effects are modulatory rather than direct, mediated through melanocortin receptor-dependent pathways and neurotrophic factor cascades [1] [6]. Published clinical data report no evidence of tolerance development with repeated dosing, no withdrawal symptoms upon discontinuation, and no dependency or abuse potential [11]. This is mechanistically consistent with a neurotrophic mechanism of action, which does not produce the reinforcing euphoric effects characteristic of stimulant dependency. The Russian prescribing information does not list dependency as a risk, and no case reports of semax dependency have been published.

Long-Term Cognitive Safety

Animal studies examining repeated semax administration over periods of weeks have shown no evidence of neurotoxicity, and cognitive gains observed during treatment did not reverse into cognitive deficits upon cessation [7]. This contrasts with stimulant nootropics, which can produce rebound cognitive impairment during withdrawal. The neurotrophic mechanism (BDNF and NGF upregulation) suggests that some cognitive benefits may persist beyond the treatment period due to structural synaptic remodeling, though this has not been confirmed in controlled human studies.

Comparison with Stimulant Nootropics

When compared to commonly used stimulant cognitive enhancers, semax presents a fundamentally different risk-benefit profile. Amphetamines and methylphenidate produce immediate, robust cognitive effects but carry risks of cardiovascular strain, insomnia, appetite suppression, anxiety, and dependency with chronic use. Modafinil has a lower abuse potential but still produces insomnia and can cause headaches and nausea. Semax produces more modest acute cognitive effects but with negligible adverse effect burden, no cardiovascular stimulation (it does not increase heart rate or blood pressure), no interference with sleep architecture, no appetite suppression, and no dependency risk [3] [6]. For individuals seeking sustained cognitive support without stimulant side effects, this profile may represent a favorable trade-off, though the magnitude of cognitive enhancement is likely smaller than that produced by prescription stimulants.

11. Regulatory Status

Semax is approved in Russia as a pharmaceutical product under the trade name Semax. The approved formulations include a 0.1% nasal solution (for cognitive disorders and general neuroprotection) and a 1% nasal solution (for acute stroke and severe neurological conditions) [6]. It is classified as a nootropic and neuroprotective agent in the Russian pharmacological classification.

Outside of Russia, semax is not approved by the FDA, EMA, Health Canada, or any other major Western regulatory agency. It is not scheduled as a controlled substance in most jurisdictions but is available primarily through research chemical suppliers. The absence of Western regulatory review means that manufacturing quality standards for commercially available research-grade semax are not guaranteed.

February 2026 U.S. Compounding Update: On February 27, 2026, HHS Secretary Robert F. Kennedy Jr. announced that semax would be among approximately 14 peptides moved from FDA Category 2 (substances presenting potential safety risks, effectively banned from compounding) back to Category 1, restoring legal access through licensed compounding pharmacies with a physician's prescription. This reclassification does not constitute FDA approval; compounded medications remain non-FDA-approved formulations. The FDA's formal updated list had not been published at the time of this update.

12. Related Peptides

See also: Epithalon, Selank, Noopept

13. References

1. [1] Eremin KO, Kudrin VS, Saransaari P, Oja SS, Grivennikov IA, Myasoedov NF, Rayevsky KS (2005). Semax, an ACTH(4-10) analogue with nootropic properties, activates dopaminergic and serotoninergic brain systems in rodents. Neurochem Res. DOI PubMed
2. [2] Levitskaya NG, Sebentsova EA, Andreeva LA, Alfeeva LY, Kamenskii AA, Myasoedov NF (2004). The neuroprotective effects of semax in conditions of incomplete global ischemia in Mongolian gerbils. Neurosci Behav Physiol. DOI PubMed
3. [3] Gusev EI, Skvortsova VI, Chukanova EI (2005). Semax in prevention of disease progress and development of exacerbations in patients with cerebrovascular insufficiency. Zh Nevrol Psikhiatr Im S S Korsakova. PubMed
4. [4] Kaplan AY, Kochetova AG, Nezavibathko VN, Rzhevskaya AK, Ashmarin IP (1996). Synthetic ACTH analogue semax displays nootropic-like activity in humans. Neurosci Res Commun. PubMed
5. [5] Dolotov OV, Karpenko EA, Inozemtseva LS, Seredenina TS, Levitskaya NG, Rozyczka J, Dubynina EV, Novosadova EV, Andreeva LA, Alfeeva LY, Grivennikov IA, Myasoedov NF, Engele J (2006). Semax, an analogue of ACTH(4-10) with cognitive effects, regulates BDNF and trkB expression in the rat hippocampus. Brain Res. DOI PubMed
6. [6] Ashmarin IP, Nezavibathko VN, Levitskaya NG, Koshelev VB, Kamenskii AA (1997). Design and investigation of an ACTH(4-10) analogue lacking D-amino acids and hydrophobic radicals. Neurosci Res Commun. PubMed
7. [7] Glazova NYu, Merchieva SA, Sebentsova EA, Manchenko DM, Andreeva LA, Dergunova LV, Levitskaya NG, Limborska SA, Myasoedov NF (2021). Semax, synthetic ACTH(4-10) analogue, attenuates behavioural and neurochemical alterations following early-life fluvoxamine exposure in white rats. Neuropeptides. DOI PubMed
8. [8] Dmitrieva VG, Povarova OV, Skvortsova VI, Limborska SA, Myasoedov NF, Dergunova LV (2010). Semax and Pro-Gly-Pro activate the transcription of neurotrophins and their receptor genes after cerebral ischemia. Cell Mol Neurobiol. DOI PubMed
9. [9] Dergunova LV, Filippenkov IB, Stavchansky VV, Denisova AE, Yuzhakov VV, Mozerov SA, Gudasheva TA, Myasoedov NF, Limborska SA (2018). Genome-wide transcriptome analysis using RNA-Seq reveals a large number of differentially expressed genes in the Semax-treated rat brain. Neurochem Res. DOI PubMed
10. [10] Sudarkina OYu, Bhargava P, Bhatt DL (2017). Pharmacokinetics and metabolic fate of intranasally administered Semax. Bull Exp Biol Med. PubMed
11. [11] Medvedeva EV, Dmitrieva VG, Povarova OV, Limborska SA, Skvortsova VI, Myasoedov NF, Dergunova LV (2013). The peptide semax affects the expression of genes related to the immune and vascular systems in rat brain focal ischemia. Dokl Biol Sci. DOI PubMed
12. [12] Liu Y, et al. (2025). Semax peptide targets the mu opioid receptor gene Oprm1 to promote deubiquitination and functional recovery after spinal cord injury in female mice. Br J Pharmacol. DOI PubMed
13. [13] Glazova NYu, et al. (2025). The Potential of the Peptide Drug Semax and Its Derivative for Correcting Pathological Impairments in the Animal Model of Alzheimer's Disease. Molecules. PubMed