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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 1970, the American immunologist Victor Najjar described a short, natural tetrapeptide, which he named tuftsin (from Tufts University, where he worked). The Thr-Lys-Pro-Arg sequence comes from the Fc fragment of the immunoglobulin G heavy chain (positions 289–292) and is formed physiologically by the enzymatic cleavage of IgG in the spleen and by neutrophil membrane enzymes. Function: stimulating the phagocytic activity of macrophages and neutrophils. Tuftsin was initially treated solely as an immunomodulatory peptide.
Two decades later, a group of Russian researchers at the Institute of Molecular Genetics in Moscow – led by Nina Myasoedov and with the participation of Ashmarin’s team – began to test synthetic analogues of tuftsin for neurobiological activity. The hypothesis was not obvious: since tuftsin modulates immune functions, and the immune system is closely related to the stress axis (HPA) and emotional reactions, perhaps tuftsin analogues may have anxiolytic activity. The hypothesis turned out to be correct. In 1995, the team described Selank — heptapeptide with the sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro, which showed strong anxiolytic effects in behavioral tests in animal models without sedation characteristic of benzodiazepines.
This distinction—anxiolysis without sedation—is the central argument for Selank research. Classic benzodiazepines solve the problem of anxiety, but at the same time they introduce sedation, working memory disorders, ataxia and – with long-term administration – tolerance and addiction. Selank in animal models and clinical trials vs. medazepam does not show these side effects, offering a pharmacologically purer anxiolytic action profile.
📖 The following article is educational and is a review of published scientific literature about Selank. 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).
Selank is a synthetic heptapeptide sequence Thr-Lys-Pro-Arg-Pro-Gly-Pro (single letter: TKPRPGP). The first four amino acids correspond to the sequence of tuftsin — natural immunomodulatory peptide derived from the Fc fragment of IgG. C-terminal tripeptide Pro-Gly-Pro is a synthetic extension introduced intentionally to increase proteolytic stability, identical in design strategy to the other peptide of the Russian school – Semax.
Chemical features important from a laboratory perspective:
The Pro-Gly-Pro stabilization strategy is particularly important here. Tuftsin in human serum is degraded within 5–10 minutes by aminopeptidases and carboxypeptidases, making it impractical as a research tool. Selank retains its molecular structure for several dozen minutes to several hours, which enables the observation of pharmacodynamic effects in behavioral experiments.
Selank acts through several parallel neurobiological pathways, but the predominant activity profile results from modulation of the GABA inhibitory system. The following sections rank the mechanisms in order of the most documented.
The effects of Selank on GABAergic neurotransmission have been documented at two overlapping levels:
The mechanism is fundamentally different from that of benzodiazepines. Benzodiazepines act as direct allosteric modulators of the alpha-gamma site on the already existing GABA-A receptor. Selank – although also allosteric – combines modulation with a transcriptional effect and does not cause side effects typical of benzodiazepines: sedation, ataxia, tolerance, addiction.
Individual works suggest an increase in expression brain neurotrophic factor (BDNF) in the hippocampus and cortex after Selank – a smaller and less consistent effect than with Semax, although direct head-to-head comparisons of both peptides are limited. The increase in BDNF is one of the mechanisms by which Selank may produce effects on cognitive functions and resistance to chronic stress.
Selank – similarly to Semax – inhibits the activity of enkephalin-degrading enzymes in human serum (Kost et al., 2001). This mechanism translates into an increase in the concentration of endogenous enkephalins (Met-enkephalin and Leu-enkephalin). The opioid activity of endogenous peptides probably contributes to the anxiolytic and mood-stabilizing effect – although the magnitude of this effect is smaller than the effect on the GABA system.
In models of chronic stress, Selank modulates the activity of the hypothalamic-pituitary-adrenal (HPA) axis. The peptide reduces the excessive corticosterone response in stressful situations, but does not suppress basal axis activity — does not cause a decrease in endogenous cortisol at rest. This profile distinguishes Selank from drugs that lower systemic cortisol levels (e.g., mifepristone) and is important for studies of stress resistance without compromising underlying hormonal regulation.
Selank retains some of its tuftsin-like activity – it modulates macrophage function and influences the cytokine profile. In individual studies Russian-speaking people activity has been demonstrated against influenza viruses in in vitro models and in mice, but the data are fragmentary and have not been validated in independent Western work. These effects remain peripheral to mainstream research on anxiolysis.
Some studies indicate modulation of serotonin metabolism – an increase in 5-HT concentration in the cortex and hippocampus after Selank administration. The mechanism is not fully described; may result from inhibition of monoamine-degrading enzymes or modulation of serotonin release in specific brain areas.
The most consistent and repeatable pool of data concerns classic behavioral tests modeling anxiety in rodents:
The magnitude of the effect is comparable to moderate benzodiazepines (e.g., medazepam) in some behavioral parameters – especially in tests measuring avoidance of novel situations. Critical difference: Selank does not cause the concurrent impairment of motor coordination (rotarod test, open field coordination) that accompanies benzodiazepines.
Some work suggests the antidepressant effects of Selank in animal models – particularly in forced swimming (Porsolt) and tail suspension tests. The effect is not as strong as classic SSRIs, but observed consistently. The mechanism is probably related to the modulation of BDNF and an indirect effect on the serotonergic system.
Selank increases the behavioral resistance of animals to chronic stress – both physical (immobilization, cold stress) and psychosocial (defeat model). In these models, the peptide reduces:
Some experimental work models the consolidation of emotional memory (fear conditioning) and resistance to traumatic stimuli in rodents. In these models, Selank reduces anxiety and avoidance symptoms developing weeks after exposure. The mechanism probably involves modulation of synaptic plasticity in the amygdala and hippocampus. It should be noted, however, that there are no validated animal models specifically reflecting clinical PTSD, so extrapolation to this indication would require clinical work.
Although Selank is classified primarily as an anxiolytic, it has demonstrated moderate improving effects in tests of memory and learning (Morris water maze, passive avoidance) – especially in conditions where cognitive function is impaired by stress or anxiety. In baseline states, the procognitive effect is weaker than in the case of Semax, but it is also present in monkeys under stress conditions (Semenova et al., 2008).
Selank has been registered as a drug in the Russian Federation in 2009 (0.15% intranasal solution), based on multicenter clinical studies by Zozulya et al. (2008) in generalized anxiety disorder (GAD) and neurasthenia. In a comparative trial with medazepam, Selank demonstrated comparable anxiolytic efficacy on the Hamilton and Zung scales, with additional antisthenic and cognitive stimulant effects that medazepam did not have. However, the limitations of these studies are known: small samples, non-uniform randomization, limited blinding, publications mainly in Russian-language journals. For this reason, Selank has not been registered by the EMA or FDA.
Selank, similarly to Semax, is most often administered in several ways:
The intranasal route of administration is preferred due to the higher peptide concentrations achieved in brain structures at lower total doses. Peptide calculator helps calculate the amount of bacteriostatic water for reconstitution of the lyophilized product in accordance with the parameters of the planned experiment.
Selank from the One Peptides catalog meets the following quality criteria:
| Parameter | Specification | Method |
|---|---|---|
| Cleanliness | ≥98% | RP-HPLC |
| Molecular mass identity | 751.89 Da | ESI-MS |
| Summary formula | C₃₃H₅₇N₁₁O₉ | — |
| 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 linked to a certificate of analysis (COA), publicly available on the website quality tests and certificates. A cold chain of 2–8°C is maintained from synthesis to delivery.
Selank – thanks to the C-terminal Pro-Gly-Pro sequence – shows good stability for a heptapeptide:
For a complete guide to storing peptides, see the article laboratory practice with research peptides.
In animal models, Selank has a favorable safety profile. Toxicology compilations did not show an LD₅₀ threshold within the range of preclinical doses tested (Kolomin et al., 2013). Key Feature: no sedation, no ataxia, no typical effects of sedative anxiolytics in clinical protocols vs. medazepam.
Clinical literature in Russia reported:
Interactions typical of benzodiazepines (alcohol potentiation, respiratory depression) have not been systematically tested in published work – Selank’s mechanism does not suggest such a risk, but formal validation of the interaction remains a task for future work.
⚠️ Most of the data comes from research groups in the Russian Federation. Independent replications by Western teams are less numerous. There is no clinical data from large trials compliant with EMA/FDA standards. Validation of long-term safety remains limited – although the first decade of clinical use of Selank in Russia did not generate warning signals.
Specific limitations to keep in mind:
Mechanistically and clinically. Benzodiazepines act as direct allosteric modulators of the GABA-A receptor – they bind to the benzodiazepine site and enhance the effect of endogenous GABA. Effect: strong, rapid anxiolytic and sedative effect, but also tolerance, addiction, memory disorders, ataxia. Selank acts in two overlapping ways: as a positive allosteric modulator of GABA binding (Vyunova 2018) and as a modulator of GABA-A receptor gene expression and related pathways (Volkova 2016). The binding site of Selank does not fully coincide with the benzodiazepine site – the effect develops in different directions and is not accompanied by sedation or withdrawal symptoms.
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 tuftsin – a natural tetrapeptide (Thr-Lys-Pro-Arg) described in 1970 by Victor Najjar at Tufts University. Tuftsin is an Fc fragment of the immunoglobulin G heavy chain (positions 289–292) and is produced by the enzymatic cleavage of IgG in the spleen and by neutrophil membrane enzymes. The physiological function of tuftsin is to stimulate the phagocytic activity of macrophages. Selank was created by adding the synthetic tripeptide Pro-Gly-Pro to the C-terminus of tuftsin – this procedure increased the proteolytic stability many times and revealed the previously invisible anxiolytic activity of the molecule.
No addictive potential was observed in animal models. Selank does not bind directly to the benzodiazepine site or opioid receptors in a way that induces tolerance or abstinence. In clinical observations in Russia (short and medium term), no withdrawal syndrome was reported after completion of the protocol. This is a significant advantage over benzodiazepines, the addiction of which develops within a few weeks of regular administration.
Mechanistically – Semax works mainly through the dopamine-serotoninergic system and has a nootropic profile (enhances learning, memory, neuroprotection). Selank acts mainly through the GABAergic system and has an anxiolytic profile. In research practice, they are often treated as a complementary pair – an activating nootropic (Semax) and a calming anxiolytic (Selank).
Yes, as an analogue of tuftsin, it retains some of its immunomodulatory activity. In animal models, it modulates macrophage function and influences the cytokine profile. Single Russian-language studies suggest activity against influenza viruses in in vitro models and in rodents – fragmentary data, lack of independent Western validation. These effects are peripheral to the main 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.
In animal models, the anxiolytic effect was observed after a single administration – both in the elevated plus maze and open field tests. This distinguishes Selank from classic SSRIs (which require weeks for anxiolytic effect), but makes its pharmacodynamic profile similar to benzodiazepines. The critical difference is that benzodiazepines also cause sedation after the first dose – Selank does not.
Selank 10 mg is available in the One Peptides catalog in a lyophilized vial, with full QC documentation and a certificate of analysis for each batch. Maintaining a cold chain of 2–8°C during transport and storage is an operational standard – crucial for regulatory peptides of this molecular weight.
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. 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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