Semax and Selank look like twins. They were built at the same Moscow institute, they are both seven amino acids long, and they end in the same three building blocks. But the front half of each was copied from a different part of the body, one from a stress hormone and one from the immune system. That single difference sent their research in two directions: brain injury and learning for Semax, stress and anxiety for Selank.
The short answer
Semax and Selank share a tail and differ in their heads. Each is a seven-amino-acid peptide built from a short natural fragment plus the same stabilizing tail, Pro-Gly-Pro. Semax's fragment comes from ACTH, a stress hormone, and its research centers on brain growth factors such as BDNF. Selank's fragment comes from tuftsin, a peptide of the immune system, and its research centers on the brain's calming signals, chiefly GABA. Both are registered medicines in Russia. Neither is approved by the FDA.
An analogy that holds up
Picture two keys cut on the same blank.
The blank is Pro-Gly-Pro. It is sturdy and hard for the body's enzymes to wear down, so a peptide fitted with it lasts longer than its natural fragment would alone.
The cut is the fragment at the front, and it decides which lock the key fits. Semax's cut is copied from a hormone involved in the stress response. Selank's cut is copied from an immune peptide. Same blank, different cuts, different doors.
Side by side
| Semax | Selank | |
|---|---|---|
| Developed | Institute of Molecular Genetics, Russian Academy of Sciences, Moscow (1980s) | Institute of Molecular Genetics with the Zakusov Institute of Pharmacology, Moscow |
| Sequence | Met-Glu-His-Phe-Pro-Gly-Pro | Thr-Lys-Pro-Arg-Pro-Gly-Pro |
| The "head" | ACTH(4–7), a fragment of the stress hormone ACTH | Tuftsin, a fragment of an immune-system antibody |
| The "tail" | Pro-Gly-Pro | Pro-Gly-Pro |
| Main research focus | Brain growth factors (BDNF, NGF), recovery after reduced blood flow, learning in animal models | Anxiety-like behavior, the GABA system, enkephalin breakdown |
| Hormonal activity | Lacks the hormone-releasing activity of full ACTH | None reported |
| Regulatory status | Registered in Russia; not FDA or EMA approved | Registered in Russia; not FDA or EMA approved |
| Evidence tier | D to E | D to E |
The shared tail
Most short peptides are broken down within minutes by enzymes called peptidases. Pro-Gly-Pro is a fragment found in collagen, and it is unusually resistant to them. Adding it to the end of a short fragment was the design idea both molecules share. It was meant to let a brief natural signal last long enough to be studied.
That shared design is the main reason the two are grouped together. It says nothing about what each one does.
Semax in more detail
Full-length ACTH is a hormone of 39 amino acids that tells the adrenal glands to release cortisol. Researchers in the Soviet Union had noticed that short fragments of ACTH seemed to affect attention and learning in animals without triggering that hormonal effect. Semax takes one of those fragments, positions 4 to 7, and adds the Pro-Gly-Pro tail.
In rodent studies, Semax raises levels of BDNF (brain-derived neurotrophic factor) and its receptor in the hippocampus, a region central to memory. BDNF supports the survival of nerve cells and the formation of new connections between them. Semax has also been studied in animal models of reduced blood flow to the brain, and it interacts with the melanocortin system, the receptor family ACTH belongs to.
In Russia, Semax is a registered medicine and has a clinical literature of its own. Independent replication outside Russia is thin, which is why it sits low on the evidence ladder despite decades of use there. In July 2026 an FDA advisory committee recommended Semax for the pharmacy compounding list. That vote is advisory and is not an approval.
Selank in more detail
Tuftsin is a four-amino-acid fragment of an antibody and is known for its role in immune signaling. Selank adds the Pro-Gly-Pro tail to it.
In animal models, Selank shows anxiety-reducing effects. The mechanism appears to involve several systems at once. It influences GABA signaling, the brain's main calming pathway, and it affects serotonin. It also slows the breakdown of enkephalins, the body's own opioid-like peptides, by inhibiting the enzymes that degrade them.
What makes Selank interesting to researchers is what has not been seen. In the animal studies, it did not produce the sedation, tolerance or withdrawal associated with benzodiazepines, the best-known drugs acting on the GABA system. Because of its tuftsin origin, Selank has also been studied for effects on immune signaling molecules.
Like Semax, Selank is registered in Russia and has limited independent Western data. It was not among the compounds the FDA advisory committee voted on in July 2026.
Why they are discussed together
Semax and Selank came from the same institute, use the same design strategy and end in the same tail. That makes them natural companions in the literature. But they were aimed at different questions from the start.
- Semax research asks whether a brief hormone fragment can support nerve cells and learning without acting as a hormone.
- Selank research asks whether an immune fragment can quiet stress responses without the drawbacks of existing calming drugs.
Taken together, they show how one design idea can be pointed at two quite different systems in the brain. Asking which is "better" misses the point. They were built to study different things.
The takeaway
Semax and Selank are siblings by design, not by function. Both pair a short natural fragment with the same durable Pro-Gly-Pro tail. Semax borrows from a stress hormone and is studied for brain growth factors and learning. Selank borrows from the immune system and is studied for calming signals and stress. Both have long histories in Russia and a thin evidence base elsewhere, and neither is approved in the United States.
Frequently asked questions
What is the difference between Semax and Selank?
Both are seven-amino-acid peptides ending in the stabilizing sequence Pro-Gly-Pro. Semax is built on a fragment of the hormone ACTH and is studied mainly for its effect on brain growth factors such as BDNF. Selank is built on tuftsin, an immune-system peptide, and is studied mainly for its effects on the GABA system and anxiety-like behavior in animal models.
Are Semax and Selank the same thing?
No. They share a design strategy and the same three-amino-acid tail, but the fragments at the front are different, and the research on each focuses on different systems.
Who developed Semax and Selank?
Both were developed in Moscow at the Institute of Molecular Genetics of the Russian Academy of Sciences. Selank was developed with the Zakusov Institute of Pharmacology.
Are Semax and Selank FDA approved?
No. Both are registered medicines in Russia, but neither is approved by the FDA or the European Medicines Agency. An FDA advisory committee recommended Semax for the compounding list in July 2026. That recommendation is not binding and is not an approval.
What does Pro-Gly-Pro do?
Pro-Gly-Pro is a three-amino-acid sequence found in collagen that resists breakdown by the body's enzymes. Adding it to a short peptide fragment is intended to make the fragment more stable.
What are the evidence tiers for Semax and Selank?
On PUŪRA's A–E evidence ladder, both sit at D to E. Most of the evidence comes from animal studies and Russian clinical literature, with limited independent replication elsewhere.