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A research-focused comparison of Melanotan II and PT-141, covering melanocortin receptor selectivity, evidence, safety signals and regulatory status.
In the 1960s, Dutch neuroendocrinologist David de Wied observed something that changed the way we thought about adrenocorticotropic hormone (ACTH). Classically, this hormone was treated as a simple regulator of the adrenal axis – secreted from the pituitary gland, stimulating the adrenal cortex to produce cortisol. However, De Wied showed that ACTH has a strong, cortisol-independent behavioral effect: it modifies learning, memory and the response to stress in animals after hypophysectomy (removal of the pituitary gland). What’s more, the effect persisted even after the shortened fragment was administered ACTH(4-10), which no longer had corticotropic activity. Adrenal hormone turned out to be a carrier of neurobehavioral information.
Two decades later, a Russian team led by Ivan Ashmarin at the Institute of Molecular Genetics in Moscow undertook the task of rationally modifying this fragment. Goal: maintain nootropic activity, eliminate residual hormonal activity, increase proteolytic stability. This is how it was created in 1982 Semax — heptapeptide with the sequence Met-Glu-His-Phe-Pro-Gly-Pro, which is today one of the best documented nootropic peptides in preclinical literature.
The following article is educational and is a review of published scientific literature about Semax. Most of the studies cited were conducted in animal models and in vitro; some clinical work comes from Russian-language literature, the validation of which in independent Western groups remains limited. The text does not constitute medical advice. The peptide from the One Peptides catalog is intended only for laboratory tests (Research Use Only).
Semax is a synthetic heptapeptide designed as ACTH analogue(4-10) about the sequence Met-Glu-His-Phe-Pro-Gly-Pro (single letter: MEHFPGP). The first four amino acids (Met-Glu-His-Phe) correspond to positions 4–7 of the natural ACTH sequence, while the C-terminal tripeptide Pro-Gly-Pro replaces the natural Gly-Lys-Pro fragment (4-10), protecting against proteolytic degradation and eliminating the remains of hormonal activity.
Chemical features important from a laboratory perspective:
The characteristic Pro-Gly-Pro sequence at the C-terminus protects the molecule primarily against cleavage by carboxypeptidases — the geometry of the proline residues changes the conformation of the chain and makes it difficult to fit into the active center of the enzyme. The N-terminus (Met) remains sensitive to aminopeptidases, and N-terminal hydrolysis generates the above-mentioned active metabolites. This structural solution became the hallmark of the Russian school of peptidology and is also repeated in the second known molecule from the same group – Selank.
Semax does not work through a single, isolated receptor. The molecule modulates several signaling pathways in the central nervous system in parallel, resulting in a pleiotropic activity profile observed in behavioral and molecular experiments. The following sections rank these mechanisms in order of the most documented.
The best documented mechanism of Semax is expression stimulation brain neurotrophic factor (BDNF) and nerve growth factor (NGF). Work by Dolotov and colleagues has shown that a single administration of Semax to rats increases BDNF mRNA and protein levels in the hippocampus and prefrontal cortex within 3–24 hours (Dolotov et al., 2006).
The mechanism spreads through a transcriptional cascade:
The same study showed a parallel increase in the expression of TrkB – the receptor for BDNF – which enhances the neurotrophic signal. BDNF is one of the most important regulators of synaptic plasticity and neuronal survival; its increase likely accounts for most of the observed neurocognitive effects of Semax.
A less obvious but well-described mechanism is activity inhibition enkephalinases — enzymes that degrade endogenous enkephalins (Met-enkephalin and Leu-enkephalin). In the study by Kost et al. (2001) Semax and its metabolites inhibited the activity of enkephalin-degrading enzymes in human serum. Consequence: an increase in the concentration of endogenous enkephalins in synapses, which translates into modulation of opioid and serotonergic neurotransmission.
Semax affects dopamine neurotransmission, particularly in the prefrontal cortex and striatum (Eremin et al., 2005). The mechanism involves increasing the activity of tyrosine hydroxylase (an enzyme that synthesizes dopamine) and modulating the release of dopamine in response to cognitive stimuli. The effect explains part of the peptide’s nootropic effect — especially in tests requiring attention and working memory.
In models of cerebral ischemia, Semax has a pronounced neuroprotective effect, the mechanism of which goes beyond a simple neurotrophin effect. Studies on MCAO models (middle cerebral artery occlusion) in rats showed that the peptide:
This profile distinguishes Semax from classic nootropics (e.g. piracetam) – the peptide not only improves cognitive function, but also actively protects tissue against ischemic damage.
Although Semax is designed to eliminate the hormonal activity of the ACTH fragment, individual works postulate retained partial affinity for MC4R melanocortin receptors in the central nervous system. However, this hypothesis has not been consistently validated in independent binding studies – it remains a signal for further mechanistic work, not an established pharmacological fact.
Semax’s bibliography includes several hundred experimental works from the last four decades. The following overview organizes the main lines of evidence.
The richest area of Semax research – both preclinical and clinical in the Russian Federation. MCAO and photothrombotic models in rats showed:
Clinical practice in Russia includes the use of Semax in acute ischemic stroke – although the clinical data do not meet EMA/FDA standards, the peptide is registered there as a drug in two characters: 0.1% intranasal solution (cognitive disorders, asthenia, prevention under cognitive load) and 1% intranasal solution (acute ischemic stroke, dyscirculatory brain damage) — approved for medical practice in the mid-late 1990s.
Behavioral tests – Morris water maze, passive avoidance, novel object recognition, Y-maze – consistently show improvement in learning and memory after administration of Semax. The effect is consistent with the BDNF mechanism and observed especially in models with cognitive deficit (drug model, age model, hypoxia model). Individual works have also explored nootropic effects in humans (Kaplan et al., 1996).
In a model of Parkinson’s disease (toxic MPTP induction), Semax has a protective effect on dopaminergic neurons (Levitskaya et al., 2004). Individual papers have explored models of Alzheimer’s (amyloidosis) and vascular dementia – the results are preliminary, inconsistent between models and require independent validation. The scale of the effect depends on the moment of intervention in relation to the induction of damage.
Although Semax is not classified as an anxiolytic (this role is played by a related drug Selank), in some models of experimental anxiety – especially in combination with stress exposure – the peptide shows stabilizing effects. Data regarding antidepressant effects are limited but consistent with a BDNF (key neurotrophic hypothesis of depression) mechanism.
There are clinical studies in the Russian-language literature on the use of Semax in children with attention deficit and hyperactivity. Due to the methodological limitations of these works (lack of randomization, limited blinding), they do not meet EMA/FDA registration standards, but they constitute an important direction of the research hypothesis for independent replications.
Semax is most often administered in several ways, depending on the research model:
The intranasal pharmacokinetics of Semax are exceptionally well described – the peptide reaches detectable concentrations in the cerebrospinal fluid and brain structures within a few to several minutes after application. This is one of the main arguments for choosing the intranasal route in research protocols.
Peptide calculator allows you to calculate the amount of bacteriostatic water for reconstitution of the lyophilized product in accordance with the parameters of the planned experiment.
Semax from the One Peptides catalog meets the following quality criteria:
| Parameter | Specification | Method |
|---|---|---|
| Cleanliness | ≥98% | RP-HPLC |
| Molecular mass identity | 813.93 Da | ESI-MS |
| Humidity | ≤5% | Karl Fischer |
| Endotoxins | ≤1 EU/mg | LAL test |
| Appearance | White/cream-white lyophilisate | Visual inspection |
Each vial is marked with a batch number associated with a certificate of analysis (COA). Full QC documentation is publicly available on the website quality tests and certificates — which distinguishes One Peptides’ offer from suppliers that declare purity without providing raw analytical data.
Semax – thanks to the C-terminal Pro-Gly-Pro sequence – shows good stability for a heptapeptide:
A cold chain of 2–8°C in transport and storage is standard for regulatory peptides – One Peptides maintains this regime from synthesis to delivery. For a complete guide to storing peptides, see the article laboratory practice with research peptides.
In animal models, Semax has a favorable safety profile. In the Ashmarin syndrome toxicology compilations, the LD₅₀ threshold was not reached in the tested preclinical dose range (Kolomin et al., 2013). Long-term models showed no cumulative toxicity or organotoxic effects under Russian-language protocols.
Most of the data comes from research groups in the Russian Federation. Independent replications by Western teams are much fewer. There is no clinical data from large trials compliant with EMA/FDA standards – although Semax is registered as a drug in the Russian Federation in 0.1% and 1% forms (various indications).
Specific limitations to keep in mind:
Mechanistically, Semax works mainly by modulating BDNF/NGF, the enkephalin system and partially the dopamine system – this is a different route than racetams (which affect, among others, AMPA receptors, membrane modulation and cholinergic signaling) or phenotropil (GABA and dopamine modulator). In research practice, Semax shows a stronger neuroprotective profile in ischemia models, while racetams are stronger in classical learning facilitation models.
Yes, as a research reagent (Research Use Only). RUO status means that the peptide is legally sold as a laboratory research chemical. It is not registered as a medicine with the EMA – it is not available as a pharmaceutical product for human treatment in the EU.
From pharmacokinetics. Peptides administered peripherally poorly cross the blood-brain barrier. Intranasal application allows for olfactory and trigeminal transport – the peptide reaches brain structures bypassing the barrier, in higher concentrations than when administered subcutaneously or intravenously. This solution is the standard for regulatory peptides in Russian research and clinical practice.
Not to a significant extent. Although Semax comes from a fragment of ACTH(4-10), the amino acids responsible for the full corticotropic activity of the hormone are located in positions 1-24 (mainly 11-24 for binding to the MC2R receptor in the adrenal glands). Semax retains the behavioral activity of the fragment but loses the ability to stimulate the adrenal cortex. This is a deliberate design move by the Ashmarin team.
Most short regulatory peptides are rapidly degraded by aminopeptidases (N-terminal cleavage) and carboxypeptidases (C-terminal cleavage) in serum and tissues. The Pro-Gly-Pro sequence at the C-terminus of Semax is resistant to cleavage with carboxypeptidases – prolines in the peptide bonds change the geometry of the chain and make it difficult to fit into the active center of the enzyme. The N-terminus remains sensitive to aminopeptidases, but the N-terminal hydrolysis products (EHFPGP, HFPGP) retain their own biological activity.
They come from the same research school (Institute of Molecular Genetics, Moscow) and share the same stabilization strategy (C-terminal Pro-Gly-Pro). However, they differ mechanistically – Semax mainly modulates the dopamine-serotoninergic system and has a nootropic profile, Selank acts mainly through the GABAergic system and has an anxiolytic profile.
After reconstitution in bacteriostatic water and storage in a refrigerator at 2–8°C, the peptide remains stable for 28–30 days. The lyophilisate can be stored at -20°C for 24 months before reconstitution. Freeze/thaw cycles should be avoided.
RUO catalog: see Semax in the One-Peptides catalog as a research reagent for laboratory models.
Semax 50 mg is available in the One Peptides catalog in a lyophilized vial, with full QC documentation and a certificate of analysis for each batch. For researchers planning a multi-step protocol, a peptide calculator will be helpful, which calculates the volume of bacteriostatic water for reconstitution.
Global disclaimer
All One-Peptides products are reagents intended exclusively for laboratory and scientific research (Research Use Only). They are not medicines, dietary supplements or products intended for human consumption. The information in this article is educational in nature and is a review of published scientific literature; does not constitute medical, pharmaceutical or dietary advice.
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