How Selank Is Thought to Work: Enkephalins, GABA and IL-6

LynxLab · 24 October 2026 · 8 min read

The enkephalinase, GABA receptor, BDNF and interleukin-6 findings behind Selank, what each experiment measured, and which claims remain unproven in 2026.

Photo: Trnava University, Unsplash

Nobody has found a Selank receptor. That is the first thing to know about a peptide that has been a prescription anxiolytic in Russia for years and a research chemical everywhere else. What exists instead is a set of experiments, mostly from the Institute of Molecular Genetics in Moscow, pointing at three systems: the enkephalins, the GABA receptor, and the cytokine interleukin-6. This post goes through what each study on selank measured, and then lists what is still missing.

Three proposed mechanisms for one small peptide

Selank is Thr-Lys-Pro-Arg-Pro-Gly-Pro, the immune fragment tuftsin with a stabilising Pro-Gly-Pro tail. Its clinical history is covered in the sibling post on the Selank anxiety trials against benzodiazepines. The mechanism papers run alongside those trials and were often written by the same people.

The three ideas emerged in sequence. In 2001 the Moscow group proposed that Selank slows the breakdown of enkephalins, the body's own opioid peptides. In the 2010s they turned to GABA, the brain's main inhibitory transmitter, because Selank's clinical profile looked like a benzodiazepine's.

Through the same period a separate line of work measured cytokines, especially IL-6, in patients and stressed rats. None of the three has displaced the others.

Enkephalin degradation: the 2001 enzyme study

Enkephalins are five-amino-acid opioid peptides that are destroyed within seconds by enzymes collectively called enkephalinases. In 2001 Alexander Zozulya and colleagues at the Mental Health Research Centre in Moscow measured enkephalin breakdown in the blood of patients with anxiety and phobic disorders diagnosed under DSM-IV.

Patients with generalised anxiety had a shortened enkephalin half-life and lower total enkephalinase activity, a pattern the authors read as a shortage of natural enzyme inhibitors. Patients with panic disorder and agoraphobia did not show it. In the test tube, Selank inhibited the enzymatic hydrolysis of plasma enkephalin dose-dependently, with an IC50 of 15 micromolar, and was more potent than the known peptidase inhibitors bacitracin and puromycin (Zozulya et al., Bulletin of Experimental Biology and Medicine, 2001).

The clinical follow-up came in 2008. In 62 patients with generalised anxiety disorder or neurasthenia, the half-life of leucine-enkephalin was reduced and correlated with illness duration and symptom severity. During Selank treatment it rose, and the correlation with anxiety scores strengthened, mostly in the GAD patients (Zozulya et al., Zhurnal Nevrologii i Psikhiatrii, 2008). The link between a blood enzyme measurement and a change in mood is correlation, and the authors present it as such.

GABA: the gene expression evidence

The GABA hypothesis started from the clinic rather than the bench. Selank's anxiolytic effect in Russian trials looked like that of diazepam and phenazepam, both of which work by allosteric modulation of the GABA-A receptor. In 2016 Anastasiya Volkova and colleagues asked whether the selank peptide changes the same genes that GABA itself does.

They gave rats a single intranasal dose of either Selank or GABA at 300 micrograms per kilogram, then measured 84 neurotransmission genes in the frontal cortex by real-time PCR at 1 and 3 hours. At 1 hour, 45 genes had changed expression. At 3 hours, 22 had. The changes after Selank correlated positively with the changes after GABA at the 1-hour point (Volkova et al., Frontiers in Pharmacology, 2016).

The authors' conclusion was careful: "one of its possible molecular mechanisms is associated with allosteric modulation of the GABAergic system". They also cited earlier binding work by V'yunova and colleagues in 2014 showing that Selank changed the number of specific binding sites for tritiated GABA without changing receptor affinity. Neither experiment showed Selank binding to the GABA-A receptor directly.

A 2017 behavioural study from the same institute tested the idea in another way. Rats under unpredictable chronic mild stress were given diazepam, Selank or both, and anxiety was scored in a plus-maze test. The combination restored anxiety measures to their pre-stress values, and Selank alone was most effective against anxiety induced by the dosing course itself (Kasian et al., Behavioural Neurology, 2017). The paper shows interaction with a benzodiazepine's effect; it does not show a shared receptor.

BDNF and the hippocampal transcriptome

Two further rat studies widen the picture beyond GABA. In 2008 Inozemtseva and colleagues reported that intranasal Selank regulated BDNF expression in the rat hippocampus in vivo, placing Selank alongside other Moscow peptides that affect neurotrophins. The paper appeared in Doklady Biological Sciences and only the title is indexed in English, so the size of the effect is not available to readers without the Russian text.

The more detailed study came in 2013. Kolomin and colleagues gave rats Selank at 200 micrograms per kilogram, either once or as a course, and ran cDNA microarrays on the hippocampus. After a single intranasal dose 36 genes changed by more than two-fold; after a course, 20 did. Most coded for proteins at the plasma membrane, including transmembrane proteins, which led the authors to suggest that Selank regulates ion homeostasis in hippocampal cells (Kolomin et al., Zhurnal Vysshei Nervnoi Deiatelnosti, 2013).

Gene expression studies tell a researcher which genes moved. They do not tell them which movement caused the behaviour. Anyone who wants to buy selank for a mechanism project should note that no study has yet connected a specific gene change to a specific anxiety outcome.

IL-6 and the immune findings

Selank began as an immune peptide, so the cytokine work is less of a detour than it looks. In 2008 Uchakina and colleagues took peripheral blood cells from patients with depression and healthy controls and added Selank at 10 to the minus 7 molar. In the patients' cells, Selank "completely suppressed" IL-6 gene expression; in the controls' cells it did not. At the same time the concentration of IL-6 protein in the patient cultures rose significantly, an apparent contradiction the authors did not resolve (Uchakina et al., Zhurnal Nevrologii i Psikhiatrii, 2008).

The same paper followed patients with GAD and neurasthenia over 14 days of Selank treatment and reported shifts in the Th1/Th2 cytokine balance that correlated inversely with each other. The authors concluded that Selank "can be used as a novel immunomodulator", a claim that goes beyond what the data in the abstract shows.

The animal work is cleaner. In 2021 a group at Astrakhan State Medical University put male rats through 20 days of social stress, daily 10-minute confrontations with another male. Stress raised serum IL-1 beta, IL-6 and TGF-beta 1.

Rats given Selank intraperitoneally at 100 micrograms per kilogram per day through the same 20 days had IL-1 beta, IL-6 and TNF-alpha "practically reaching control values" (Leonidovna et al., Current Reviews in Clinical and Experimental Pharmacology, 2021). It is a stress-protection result in rats, not an anti-inflammatory result in humans.

What remains unproven in 2026

Set out as a list, the gaps are larger than the findings. Laboratories working with selank for research are, in practice, working on these questions.

No receptor: a binding partner for Selank has not been identified in any tissue.
No direct GABA-A binding: the 2016 and 2014 studies show correlated gene expression and altered GABA binding-site numbers, not Selank at the receptor.
No human pharmacokinetics: there is no published measurement of how much intranasal Selank reaches the human brain, or how long it lasts.
No placebo-controlled human mechanism study: every patient biomarker, from enkephalin half-life to IL-6, was measured in open-label treatment.
No independent replication: every mechanism paper lists Institute of Molecular Genetics authors or collaborators, and Nikolai Myasoedov is a co-author on most.
No dose-response in humans: the FDA, placing Selank in category 2 of its compounding list, states that it "lacks important information regarding any safety issues raised by selank acetate administered to humans" (FDA, Certain Bulk Drug Substances, category 2).

The honest summary is that Selank has three plausible, partly overlapping mechanisms and no decisive experiment separating them. For a UK laboratory, that is the attraction. Anyone comparing selank uk suppliers should read the Volkova and Zozulya papers first; they are the best-designed in the set and both are open about their limits.

LynxLab stocks selank 10mg for research use at £24.99 a vial, tested to 99% purity, with the lab reports on the product page.

Frequently asked questions

Does Selank work on GABA receptors?

Possibly, but indirectly as far as the evidence goes. Volkova and colleagues showed in 2016 that a 300 mcg/kg dose in rats changed 45 neurotransmission genes at 1 hour in a pattern correlated with GABA's own effect, and earlier work found altered GABA binding-site numbers. No study has shown Selank binding the GABA-A receptor directly.

What does Selank do to enkephalins?

In a 2001 test-tube study Selank inhibited the enzymes that break down enkephalin in human plasma with an IC50 of 15 micromolar, more potently than bacitracin or puromycin. In a 2008 trial of 62 anxious patients, leucine-enkephalin half-life rose during Selank treatment. Whether that change causes the anxiolytic effect has not been tested.

Does Selank reduce IL-6?

In rats under 20 days of social stress, Selank at 100 mcg/kg/day brought IL-6 back towards control levels in a 2021 study. In human cells from depressed patients, a 2008 study found Selank suppressed IL-6 gene expression while IL-6 protein rose, a contradiction that has not been explained. There is no placebo-controlled human IL-6 data.

Is the Selank mechanism confirmed?

No. Three mechanisms have been proposed, enkephalinase inhibition, GABA-A modulation and cytokine regulation, and each has supporting rat or in vitro data from Moscow. No receptor has been identified, no human pharmacokinetic study has been published, and no independent laboratory outside the original research network has replicated the core findings.

Sources

Research use only

Selank from LynxLab

10mg vials from £24.99. ≥99% purity, lab report on the page. Same-day dispatch, UK stock.

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