Semax vs Selank: What Separates Two Peptides From the Same Lab

The popular shorthand is semax for focus, selank for calm. It roughly tracks what each was studied for. It also carries far more confidence than the evidence behind it.

Look at the bottom row of that table and the real difference appears. It is not about focus or calm. It is about what each peptide was measured against.

Semax was studied alongside standard rehabilitation in stroke patients.³ Selank was tested against an active drug, head to head.² A comparison against a working drug is a harder test than a comparison against usual care. On design, selank's study is the stronger one, even though it enrolled fewer people.

Fifty-two healthy participants took part. Each was scanned with resting-state fMRI three times: before, at 5 minutes, and at 20 minutes. Participants received semax, selank or placebo.⁴

The researchers named their regions before looking, which matters. Picking targets after seeing the data is how false findings get made.⁴

They chose two. The amygdala is a key region for regulating anxiety. The dorsolateral prefrontal cortex handles executive function, including working memory. Both were examined in each hemisphere.⁴

Differences appeared in one connection. It ran between the right amygdala and a region covering the fusiform, inferior and middle temporal gyri, plus the parahippocampal gyrus.⁴

A follow-up analysis then separated the two compounds. It found both general and specific effects of selank and semax on that connection. The authors say this was the first time anyone had described it.⁴

That word specific is what makes the study useful here. It means the scan could tell the two peptides apart. The popular split between them has at least one measurement behind it.

The two are usually presented as separate discoveries that happen to pair well. The author lists tell a different story.

N. F. Myasoedov is an author on the selank clinical trial. Also on the selank gene work, the selank cell work, the semax genome-wide study, the semax stress study, and the scan that compared them.²⁵⁶¹⁴

Much of that work comes from the Institute of Molecular Genetics at the Russian Academy of Sciences.⁵⁶

That explains why the two are studied together and sold together. It also means the case for each rests on a narrower base than a long reference list implies.

What is missing is independent replication in other countries. More papers from the same programme do not substitute for it. This is worth knowing before you weigh any summary that counts citations as if they were confirmations.

• Neither has a large trial in healthy people. Semax's clinical evidence is in stroke patients,³ selank's in patients with anxiety or neurasthenia.² The healthy-volunteer study measured brain connectivity only.⁴
• No study tested them in combination. They are sold and discussed as a pair. The published record does not contain a trial of the two together.
• Neither is approved in the United States. Both are supplied here as research material.
• The language barrier cuts both ways. Russian-language clinical papers are not lower quality by default. They have also had less outside scrutiny than an English trial of the same size would attract.²³