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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 1970s and 1980s, the Russian school of peptidology developed in parallel with—and often independently of—mainstream Western neuropharmacology. Research teams at the Institute of Molecular Genetics of the Russian Academy of Sciences and the Institute of Experimental Pharmacology in Moscow worked on a strategy that would only begin to be explored in Western pharmacology a decade later: take short, biologically active fragments of natural regulatory peptides, modify them to increase stability, and test them in neurobiological models as potential nootropics and anxiolytics.
Two of the most cited molecules emerged from this research program: Semax — ACTH(4-10) analogue developed in the 1980s — and Selank — an analogue of tuftsin developed in 1995. Both peptides are registered as drugs in the Russian Federation (Semax – nootropic, Selank – anxiolytic). In the European Union, the USA and most other jurisdictions, however, they remain research peptides (Research Use Only) – without therapeutic registration.
This article compares both peptides in the context of scientific research on their mechanism of action and neurobiological activity profile. For researchers planning experiments in cognitive, anxiety, or neuroprotective models, it is important to understand how these peptides differ and when one has an advantage over the other.
📖 The following article is educational and is a review of published scientific literature about Semax and Selank. Most of the cited studies were conducted in animal models and in vitro. Some of the clinical work comes from the Russian-language literature – with correspondingly limited validation in independent groups. The text does not constitute medical advice. Peptides from the One Peptides catalog are intended only for laboratory tests (Research Use Only).
In brief. Semax and Selank are synthetic heptapeptides from the Russian school of peptidology. Both end with a Pro-Gly-Pro fragment that limits rapid enzymatic degradation. They differ in origin and the neurotransmitter systems investigated: Semax is derived from ACTH(4-10) and is discussed in relation to BDNF and dopaminergic signalling, whereas Selank is a tuftsin analogue discussed in relation to GABAergic signalling and enkephalin metabolism. Much of the clinical literature is Russian-language and has limited independent validation, which is the main limitation of the evidence base. Catalogued as RUO reagents: Semax 50 mg and Selank 10 mg.
Semax and Selank were developed in Russian research centres as synthetic heptapeptides derived from different parent molecules.
Semax was developed in the 1980s at the Institute of Molecular Genetics in Moscow by a team led by Ivan Ashmarin. The starting point was the observation that a short fragment of adrenocorticotropic hormone (ACTH) – the sequence from positions 4 to 10 (Met-Glu-His-Phe-Pro-Gly-Pro) – showed nootropic activity in behavioral tests, but without corticotropic activity (it did not stimulate the adrenal glands). The researchers synthesized an analogue of this sequence with a C-terminal extension Pro-Gly-Pro stabilizing against proteolytic degradation.
Semax sequence: Met-Glu-His-Phe-Pro-Gly-Pro
Selank was developed in 1995 at the same institute, as an analogue of tuftsin — natural immunomodulatory peptide derived from an IgG fragment (Thr-Lys-Pro-Arg sequence). Again, the same structural modification was used — the addition of Pro-Gly-Pro at the C-terminus for stabilization.
Selank sequence: Thr-Lys-Pro-Arg-Pro-Gly-Pro
Both particles show a characteristic methodological approach of the Russian school:
This strategy is related to contemporary Western approaches to peptide drug design, but predated them by decades.
| Characteristic | Semax | Selank |
|---|---|---|
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| Number of amino acids | 7 | 7 |
| Molecular mass | 813.9 Da | 751.9 Da |
| Natural source peptide | ACTH (4-10) | Tuftsin |
| Year of development | 1980s | 1995 |
| Research center | Institute of Molecular Genetics, Moscow | Institute of Molecular Genetics, Moscow |
| Registration in Russia | Yes – as a nootropic | Yes – as an anxiolytic |
| Registration with EMA/FDA | Lack | Lack |
Semax is discussed mainly in relation to BDNF and dopaminergic and serotonergic signalling, while Selank is discussed in relation to GABAergic signalling and enkephalin metabolism.
This is the area where Semax and Selank differ the most. Although both peptides have central effects, they modulate different neurotransmitter systems.
Semax works through several parallel neurobiological mechanisms:
The best-documented effect of Semax — described in numerous studies by Dolotov, Ashmarin and colleagues — is to increase expression brain neurotrophic factor (BDNF) and nerve growth factor (NGF) in the hippocampus and cortex. Mechanism:
BDNF is one of the most important regulators of synaptic plasticity and neuronal survival. The increase in BDNF is the mechanism by which Semax likely produces most of the neurocognitive effects observed in behavioral studies.
Semax modulates dopaminergic activity in selected brain areas, especially the prefrontal cortex and striatum. The mechanism includes:
The effect of Semax on serotonin is weaker than on dopamine, but it is documented. The peptide modifies the activity of monoamine metabolism enzymes and affects the release of serotonin in certain areas.
Animal models of cerebral ischemia (middle cerebral artery occlusion, MCAO) have shown that Semax administered before or shortly after ischemia reduces the volume of the infarct area and improves motor function during the recovery period. The mechanism is related to anti-inflammatory and pro-neurotrophic effects.
Selank works mainly by modulating the GABAergic system:
Selank increases the expression of GABA-A receptor subunits in the cortex and hippocampus of animal models. This is a mechanism related to the action of classic anxiolytics (benzodiazepines), but it involves modulation of receptor expression, not direct binding to them.
In behavioral tests of animal models – open field test, elevated plus maze, light-dark box – Selank showed anxiolytic effects without sedation. This significantly distinguishes it from benzodiazepines, which have an anxiolytic effect but also cause sedation, coordination disorders and memory disorders.
Similar to Semax, Selank also modulates BDNF – although the effect is weaker. The increase in BDNF expression is one of the mechanisms by which Selank can influence cognitive functions and stress resistance.
Some studies suggest that Selank modulates the activity of enkephalinases (enzymes that degrade endogenous enkephalins – opioid peptides). This mechanism may contribute to the anxiolytic and analgesic effects, although data are limited.
Selank – as an analogue of tuftsin (immunomodulatory peptide) – retains some immunomodulatory activity. It affects the function of macrophages and modulates the inflammatory response. These effects, however, are peripheral – in studies on the peptide as an anxiolytic they are not the main subject of interest.
| Characteristic | Semax | Selank |
|---|---|---|
| The main neurotransmitter system | Dopamine, serotonergic | GABAergic |
| Effects on BDNF | Strong | Moderate |
| Effect on NGF | Strong | Weaker |
| Nootropic effect | Yes (main profile) | Weaker |
| Anxiolytic effect | Weaker (mainly secondary) | Yes (main profile) |
| Sedation | Lack | None (unique anxiolytic feature) |
| Neuroprotective effect | Yes (strong) | Weaker |
| Immunomodulatory effect | Lack | Yes (as an analogue of tuftsin) |
The literature describes preclinical mechanisms and limited clinical research, with a substantial part of the evidence originating from Russian-language publications.
Semax’s bibliography includes several hundred experimental works. Main directions:
The best documented therapeutic direction. MCAO models in rats have shown:
In clinical practice in the Russian Federation, Semax is used as part of a protocol for acute ischemic stroke – although clinical data do not meet EMA/FDA standards.
Behavioral tests (Morris water maze, passive avoidance, novel object recognition) showed improvement in learning and memory after administration of Semax. The effect is consistent with the BDNF mechanism.
Models of Parkinson’s disease (MPTP induction), Alzheimer’s disease (amyloidosis), experimental depression – in all of them, Semax showed mitigating effects. The magnitude of the effect varies between models.
Selank’s bibliography is smaller but consistent in the anxiolytic direction:
Open field test, elevated plus maze, light-dark box – all showed the anxiolytic effect of Selank, comparable to benzodiazepines in some parameters (time spent in the open plus arm) without their side effects (sedation, ataxia).
Some work suggests antidepressant effects in animal models—particularly in behavioral tests of anhedonia.
Selank increased resistance to chronic stress in animal models by modulating the response of the HPA (hypothalamic-pituitary-adrenal) axis.
In the Russian Federation, Semax and Selank have undergone clinical trials sufficient to be registered as drugs. However, these studies:
There are no clinical trials at the EMA and FDA that meet registration standards.
| Parameter | Semax | Selank |
|---|---|---|
| Purity (HPLC) | ≥98% | ≥98% |
| Molecular mass (MS) identity | 813.9 Da | 751.9 Da |
| Humidity (Karl Fischer) | ≤5% | ≤5% |
| Endotoxins (LAL) | ≤1 EU/mg | ≤1 EU/mg |
Each vial is marked with a batch number associated with a certificate of analysis (COA). Full QC documentation is available on the website quality tests and certificates.
The Semax 50 mg product page describes this quantity variant of the RUO reagent; 50 mg refers to the product content, not a recommended dose. This variant is currently out of stock; the link provides its specification.
Both peptides show good stability thanks to the C-terminal Pro-Gly-Pro sequence:
The procedure for dissolving the lyophilisate is described in the guide how to dissolve peptides step by step.
In animal models and in clinical Russian studies, both peptides showed a favorable safety profile:
However, methodological caveats must be taken into account – most of the data comes from Russian-language literature with limited validation in independent Western groups.
Semax is more often selected for cognitive and neuroprotection models, while Selank is more often selected for anxiety and GABAergic-modulation models.
| Purpose of the experiment | A better choice |
|---|---|
| Cognitive models (learning, memory) | Semax |
| Experimental anxiety models | Selank |
| Models of neuroprotection in ischemia | Semax |
| Models of depression | Both, with preference for Selank |
| Models of stress resistance | Selank |
| Neurodegeneration models (Alzheimer’s, Parkinson’s) | Semax |
| Models requiring BDNF stimulation | Semax (stronger effect) |
| Models requiring GABA modulation without sedation | Selank (only option in this class) |
Mechanistically – Semax works primarily through the dopamine/serotoninergic system and has a nootropic activating profile. Selank acts mainly through the GABAergic system and has an anxiolytic profile. In research practice, it is often treated as a pair – a stimulating nootropic peptide (Semax) and a calming anxiolytic (Selank).
Yes, as research reagents (Research Use Only). RUO status means that peptides are legally sold as laboratory research chemicals. They are not registered as medicines with the EMA – they are not available as a pharmaceutical product in the European Union.
NO. Even though both classes of peptides come from the Russian school of peptidology, they are different groups. Khavinson peptides (Epithalon, Vilon, Thymalin) are bioregulatory peptides with a postulated transcriptional mechanism, developed mainly in Saint Petersburg. Ashmarin’s peptides (Semax, Selank) are nootropic and anxiolytic peptides with classic receptor mechanisms, developed in Moscow.
The lack of registration is due to limitations of available clinical data. Clinical trials in Russia did not always meet the standards of randomization, blinding and double publication required by the EMA. The manufacturer has not submitted a registration application to the EMA – the registration route would require conducting new clinical trials in line with Western standards.
Some research protocols use both peptides simultaneously – using their complementary profiles (Semax activates, Selank silences). However, there are no solid clinical studies on this combination. From a mechanistic perspective, the connection seems to make sense, but would require validation in randomized trials.
No addictive effect was observed in the research models. Both peptides modulate gene or receptor expression and do not, like drugs, bind directly to dopamine receptors in a way that induces tolerance or abstinence. This is a significant advantage over benzodiazepines (which have addiction potential) and amphetamines (which cause tolerance).
Semax increases BDNF expression at the mRNA and protein levels in the hippocampus and cortex. The mechanism probably involves activation of transcription factors (CREB, NF-κB) regulating BDNF promoters. The increase in BDNF develops within 3–24 hours of administration and persists for several days. This is the main mechanism by which the peptide produces most of its neurocognitive effects.
The anxiolytic effect of Selank was observed after a single administration in animal models. In clinical practice in Russia, dosing has usually involved short-term protocols (2–4 weeks), not long-term administration. This distinguishes Selank from classic SSRIs (which require weeks for the antidepressant-anxiolytic effect).
RUO reagent: the catalog includes Semax — research reagent (product card), intended exclusively for laboratory research use.
Both peptides available in the One Peptides catalog: Semax 50 mg and Selank 10 mg. Each batch with a certificate of analysis.
ℹ️ 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. Semax and Selank are registered as drugs in the Russian Federation, but do not have registration with the EMA, FDA or other Western regulatory agencies. 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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