Selank half-life and timing: what has been measured

What is Selank's half-life?

No published half-life figure for Selank was found in the PubMed records searched on 14 October 2026. The nearest figure is on the Russian product label, which says plasma concentration by the nasal route falls progressively over 5 to 5.5 minutes (label reproduced on RLS, changed 15 July 2025). The label cites no study for it, and a fall-off time is not a half-life, which is the time for a level to halve.

The same label paragraph says Selank is detected in plasma after 30 seconds and then spreads quickly to organs and tissues, including the brain. According to the label, the absolute bioavailability is 92.8% for the nasal route, meaning the share that reaches the bloodstream compared with a direct vein route. It adds that neither unchanged Selank nor its breakdown products appear in daily urine, because tissue peptidases (enzymes that cut peptides) degrade it quickly. Each statement is a label claim, not an independently published result. The legal status page explains what the Russian registration does and does not mean elsewhere.

Evidence limits

What has not been published about Selank's pharmacokinetics?

That gap affects every question about duration. A reader cannot work out how long Selank stays in the body from the abstracts, and the label figure rests on an unnamed source. The gap does not show that Selank lasts long or short. It shows that the measurement was not found.

How is Selank broken down in the body?

Enzymes cut Selank into shorter pieces. In a 2006 Russian study using tritium-labelled peptides (peptides marked with a radioactive form of hydrogen so every fragment can be traced), the main products in blood plasma were the pentapeptide TKPRP, the tripeptide TKP and the dipeptides RP and GP; the abstract does not name the animal or give times or concentrations (Zolotarev et al., *Bioorganicheskaya Khimiya*, 2006). The same study followed Selank in brain tissue after nasal delivery in vivo, again without reported values in the abstract (Zolotarev et al., 2006).

Breakdown products may matter on their own. In mouse spleen, with no count in the abstract, the fragment Gly-Pro produced gene-expression changes that mostly matched Selank's, which the authors say might indicate an active contribution of the dipeptide to Selank's final effect; this is a finding in mice and says nothing about people (Kolomin et al., Molecular Immunology, 2014).

How fast does Selank reach the blood and brain?

The only arrival-time figure found in the sources examined for this page comes from the Russian label: by the nasal route Selank is detected in plasma at 30 seconds and then reaches brain tissue, a label claim with no study cited (label reproduced on RLS, changed 15 July 2025). No peer-reviewed paper opened for this page reports those figures. Zolotarev et al. (2006) did measure Selank in brain tissue after nasal delivery, in an animal species the abstract does not name, and its abstract gives no values. A 2016 study in two mouse strains, with no count in the abstract, found different receptor-binding changes by route, and its authors suggest pharmacokinetics may explain the gap, without reporting blood levels, in a mouse result that does not establish a human result (Vasil'eva et al., 2016).

That 2016 study compared nasal with intraperitoneal (into the abdominal cavity) administration in two mouse strains. In BALB/c mice the binding sites for one GABA receptor marker rose by 38% by the intraperitoneal route and sites for an NMDA receptor marker rose by 23% by the nasal route; the authors suggest route-specific pharmacokinetics and biotransformation explain the difference, but the abstract reports no blood or brain levels and no animal count, so it remains a suggestion from a mouse study that does not establish a human result (Vasil'eva et al., 2016).

How soon do studies of Selank record a change?

No study read for this page measured when a person first feels an effect of Selank. The shortest time points are 5 and 20 minutes, when a 2020 study scanned the brains of 52 healthy people before and after Selank, Semax or placebo and found group differences in connectivity between the right amygdala (a brain region involved in regulating anxiety) and the right temporal cortex; a scan measure in healthy people does not report how anyone feels (Panikratova et al., Doklady Biological Sciences, 2020). In rat frontal cortex, 29 genes met the study's change criteria one hour after Selank and 17 did so at three hours, with ten rats assigned per group, five sampled at each time point and tissue pooled; these are animal gene measurements, not clinical outcomes, and they do not establish a human result (Volkova et al., Frontiers in Pharmacology, 2016, Table 1).

Semax was in the same 2020 scan study of 52 healthy people, which measured connectivity on scans only and supports no inference about symptoms or onset (Panikratova et al., 2020). It gives no separate onset time for either peptide. No paper found compared how fast the two act, so a statement that one acts faster has no support in these records. The Selank vs Semax page sets out how the two peptides differ in design.

How long do Selank's effects last, according to studies?

No human study found measured how long the effects of a single administration last. Animal studies give time points. In mouse spleen, with no count in the abstract, the C3 gene's activity fell threefold 30 minutes after one intraperitoneal administration, and the Xcr1 gene's activity fell 90 minutes after, which is a gene reading in mice that does not establish a human result and is not a duration of effect in people (Kolomin et al., Molecular Immunology, 2014). In mouse spleen, 34 of 84 inflammation-related genes analysed had changed when measured 6 and 24 hours after one administration, with no count in the abstract, again an animal gene reading that does not establish a human result (Kolomin et al., Regulatory Peptides, 2011). A 2014 study in 60 patients with phobic-anxiety and somatoform disorders, compared with phenazepam and reporting no placebo group in its abstract, says the anxiolytic effect lasted a week after the last administration of a course (Medvedev et al., 2014).

In a four-week experiment in 24 Wistar rats in three groups, anxiety-phobic scores were lower from the second day and the effect held through week four, a result in rats only that does not establish a human result (Czabak-Garbacz et al., *Pharmacological Reports*, 2006). Each time point answers a different question: gene activity in a tissue, a behaviour score or a clinician's rating. None is a measured duration of a single administration. The Selank side-effects page covers the tolerability records.

Why can blood levels and effects last for different lengths of time?

Pharmacokinetics describes what the body does to a compound: absorption, distribution, breakdown and removal, usually shown as a concentration over time. Pharmacodynamics describes what the compound does to the body. The two can run on different clocks. For Selank, the Russian label says plasma concentration falls over 5 to 5.5 minutes by the nasal route, a label claim with no study cited (RLS, changed 15 July 2025). In mouse spleen, with no count in the abstract, the C3 and Xcr1 genes changed 30 and 90 minutes after one intraperitoneal administration, an animal gene reading that does not establish a human result (Kolomin et al., Molecular Immunology, 2014). In a separate mouse-spleen study, 34 of 84 inflammation-related genes analysed had changed 6 and 24 hours after one administration, with no count in the abstract, again an animal gene reading that does not establish a human result (Kolomin et al., Regulatory Peptides, 2011). In 60 patients with phobic-anxiety and somatoform disorders compared with phenazepam, with no placebo group in the abstract, an anxiolytic effect was reported a week after the last administration (Medvedev et al., 2014). The records do not say whether a link exists between these separate measurements.

A short blood level does not by itself prove a short effect, and a long effect does not prove a long blood level. A peptide can set off changes inside cells that continue after the peptide has gone, but no study read for this page tested that for Selank. A person reading a time point should check what was measured: a concentration, a gene, a score or a scan.