What Selank is
Selank is a peptide — a short chain of amino acids, the molecules proteins are built from — made synthetically. It was modelled on a natural peptide involved in the workings of the immune system.
A small tail was added to its structure, making the peptide more stable and slower to break down in the body. In the literature it is described mainly as an investigational anti-anxiety agent that works differently from typical sedatives. In Russia it is registered as a medicine in the form of nasal drops.
It must be said plainly, though, that the overwhelming majority of the data comes from Russian studies, including small human trials. Large independent trials are so far missing. A review of the available work is here: efficacy and action of Selank in anxiety (PubMed).
How it works (in short)
Selank acts in several ways at once, and this is still being investigated. The most frequently described is its effect on the GABA system — the body's natural mechanism for quietening and calming nerve cells. Supporting that mechanism may reduce anxiety. This is described here: Selank and the GABA system in cells (Frontiers).
A second thread is its effect on enkephalins — the body's own molecules that ease pain and lift mood. Selank may slow their breakdown so they act for longer. That mechanism is described in the paper cited above.
A third effect concerns BDNF, a protein that helps nerve cells grow and form new connections (which matters for memory). In a rat study Selank raised its level in the brain: Selank and BDNF in the rat brain (PubMed). These results are preliminary and need confirmation.
What is being studied
The best-studied area is the reduction of anxiety. In a human study Selank was compared with a classic sedative in 62 people with anxiety and nervous exhaustion. The anti-anxiety effect was similar, and Selank additionally added energy, which the comparator did not: Selank versus a sedative (PubMed).
Studies noted that Selank did not cause the drowsiness, memory impairment or dependence typical of sedatives. Its possible effect on brain protection and memory is also studied: Selank and GABA-system genes (PMC).
Because it derives from a natural immune peptide, its effect on the immune system and on inflammation under chronic stress is studied too. All of these applications remain at the research stage — mainly animal work and small, largely Russian human studies. Large independent trials are lacking.
For in-vitro laboratory research only. Not for human or animal consumption and not for treatment.