Semax vs Selank: Two Moscow Peptides, Two Different Mechanisms

They were designed in the same laboratory, by the same team, using the same clever trick to make them last. They both end in the same three amino acids. They are both registered medicines in Russia, both studied for effects on the brain, and both are often sold side by side. Yet Semax and Selank start from completely different molecules, one a fragment of a stress hormone and the other a fragment of an immune peptide, and research suggests they work on the brain in quite different ways.

This guide explains where each came from, the shared design idea behind them, what the key studies found, how their mechanisms differ, and why researchers so often study them together. Both are supplied by Crown Peptides for laboratory research use only.

One Institute, One Idea

Semax and Selank were both developed at the Institute of Molecular Genetics of the Russian Academy of Sciences in Moscow, in a programme led by the chemist Nikolai Myasoedov. The programme’s goal was to take short, naturally occurring regulatory peptides with interesting effects on the brain or immune system and turn them into stable, usable compounds.

The problem with natural fragments

Short natural peptides are often broken down within minutes by enzymes in the blood and tissues. That makes them fascinating to study but difficult to use. The Moscow team needed a way to protect them without changing what made them active.

The PGP solution

Their answer was to attach a short tail of three amino acids, proline-glycine-proline, or PGP, to the end of each active fragment. Proline is unusually rigid, and sequences rich in proline are poorly recognised by many peptidases. The PGP tail slows breakdown and extends each peptide’s activity. It is the shared signature of both Semax and Selank, and it is also thought to carry some biological activity of its own. The same approach could in principle be applied to many other short regulatory peptides, which makes the Moscow programme an interesting case study in peptide design as well as in neuroscience.

Semax: A Stress Hormone Fragment Without the Stress Hormone

Semax is a seven-amino-acid peptide: Met-Glu-His-Phe-Pro-Gly-Pro. Its first four amino acids come from positions 4 to 7 of ACTH, adrenocorticotropic hormone, the pituitary hormone that tells the adrenal glands to release cortisol. The last three are the PGP tail.

Why an ACTH fragment?

From the 1960s onwards, researchers found that short fragments of ACTH, particularly the region around positions 4 to 10, affected learning, attention and memory in animals, without stimulating the adrenal glands. Those effects on the brain appeared to be separate from ACTH’s hormonal job. The Moscow team took the 4 to 7 fragment, added the PGP tail and produced a stable molecule with those brain-related effects but no cortisol-releasing activity.

BDNF: the key finding

Much of Semax’s modern research centres on brain-derived neurotrophic factor, or BDNF, a protein that supports the survival of neurons, the growth of new connections and the strengthening of synapses during learning. In a 2006 study in Brain Research, Dolotov and colleagues found that a single application of Semax in rats increased BDNF protein in the hippocampus, the brain’s key memory region, about 1.4-fold, along with a 1.6-fold increase in activation of its receptor, TrkB, and a three-fold rise in BDNF gene activity (PMID: 16996037). Treated rats also showed improved performance on a learning task. The authors suggested that Semax affects cognitive function by modulating the hippocampal BDNF/TrkB system.

A 2007 study in Neuroscience Letters by Agapova and colleagues found that a single intranasal application of Semax rapidly increased the expression of both BDNF and nerve growth factor genes in the rat hippocampus, with further region-specific changes elsewhere in the brain (PMID: 17353092).

A longer history: hormone fragments as brain tools

The idea behind Semax has deep roots. In the 1960s and 1970s, the Dutch pharmacologist David de Wied at Utrecht University showed that small fragments of ACTH, and of related pituitary hormones, changed how rats learned and remembered, for example in avoidance tasks, even when those fragments had no effect on the adrenal glands. His work introduced the idea of neuropeptides: short pieces of hormones acting directly on the brain as signals in their own right. Pharmaceutical groups went on to design stabilised ACTH fragment analogues to explore the idea further. Semax is the Moscow programme’s contribution to that tradition, and its PGP tail was one of the more successful answers to the problem of keeping such fragments active long enough to study.

Brain growth factors in plain English

Because so much Semax research centres on them, it is worth understanding what BDNF and nerve growth factor actually do. Neurotrophic factors are proteins that neurons need to survive, grow and form connections, a little like fertiliser for the brain’s wiring. BDNF is especially important in the hippocampus and cortex, where it strengthens synapses during learning, a process at the heart of memory formation. It acts mainly through a receptor called TrkB. Nerve growth factor, the first neurotrophic factor ever discovered, supports particular groups of neurons, including some involved in attention and memory. After a stroke, neurotrophic factors are thought to help surviving neurons form new connections that support recovery, which is why raising them has become such an important research goal.

Stroke research

Semax is best known in Russia for its use in stroke, and it has been studied extensively in that setting. In a 2018 study in the Zhurnal Nevrologii i Psikhiatrii imeni S.S. Korsakova, Gusev and colleagues in Moscow followed 110 patients undergoing rehabilitation after ischaemic stroke, with or without Semax (PMID: 29798983). Semax increased plasma BDNF levels, which stayed high throughout the study, and was associated with faster functional recovery, better motor performance and improved scores on the Barthel index, a standard measure of independence in daily activities. The authors concluded that early rehabilitation together with Semax increased BDNF and sped functional recovery.

Laboratory research has explored how. A 2024 study in Biomedicines by Filippenkov and colleagues used RNA sequencing to examine gene activity in the rat brain a day after experimental stroke, finding thousands of genes disrupted by ischaemia and showing that Semax and a related ACTH-derived peptide helped compensate for the disrupted gene expression profile (PMID: 39767736, PMC11673339).

Our Semax research guide covers its full history.

Selank: An Immune Peptide Turned Calming Signal

Selank is also a seven-amino-acid peptide: Thr-Lys-Pro-Arg-Pro-Gly-Pro. Its first four amino acids are tuftsin, a naturally occurring immune peptide, and the last three are the same PGP tail.

What is tuftsin?

Tuftsin was discovered in 1970 by Victor Najjar and colleagues at Tufts University, which gave it its name. It is a four-amino-acid fragment released from part of the antibody immunoglobulin G, and it stimulates immune cells, particularly phagocytes, the cells that engulf and destroy microbes. Researchers later noticed that tuftsin also had effects on the brain and behaviour. The Moscow team added the PGP tail to create a more stable molecule, and Selank was born.

The GABA connection

Clinical studies in Russia described Selank’s effects as resembling those of benzodiazepines, the class of anti-anxiety medicines that act on the brain’s main calming system, GABA. That raised the question of whether Selank works through the same system.

In a 2016 study in Frontiers in Pharmacology, Volkova and colleagues at the Institute of Molecular Genetics measured the activity of 84 genes involved in neurotransmission, including GABA receptor subunits, transporters, ion channels and dopamine and serotonin receptors, in the frontal cortex of rats one and three hours after giving Selank or GABA itself (PMID: 26924987, PMC4757669). Both changed the expression of a large number of genes, 45 at one hour and 22 at three hours, and the pattern of changes overlapped substantially between Selank and GABA. The findings supported the idea that Selank’s effects are linked to the GABA system, though through a different route from benzodiazepines, which act directly on GABA receptors.

A 2014 study in the same Russian neurology journal compared the anti-anxiety effect and tolerability of Selank with phenazepam, a benzodiazepine widely used in Russia, in patients with anxiety disorders (PMID: 25176261).

Tuftsin’s surprising second life

Victor Najjar’s work on tuftsin revealed something unexpected about the spleen. Tuftsin is cut from its parent antibody by enzymes, partly in the spleen, and Najjar reported that people without a functioning spleen, and some families with an inherited defect, had low tuftsin activity and reduced ability of their phagocytes to fight infection. For years, tuftsin was studied almost entirely as an immune peptide. Its effects on the brain, and particularly on behaviour and emotional state in animals, emerged later, and it was that second life that the Moscow team built on with Selank.

The calming system in plain English

GABA, short for gamma-aminobutyric acid, is the brain’s main inhibitory messenger. Where excitatory messengers such as glutamate tell neurons to fire, GABA tells them to slow down. A healthy brain depends on a balance between the two. Many anti-anxiety and sleep medicines, including benzodiazepines, work by making GABA receptors respond more strongly to GABA. The GABA system is also built from many different receptor subunits and supporting proteins, whose levels the brain adjusts constantly. The Selank gene expression study measured exactly those components, which is why its overlap with GABA’s own effects was such an interesting finding: it pointed to Selank influencing how the calming system is built and tuned, rather than simply pressing its accelerator.

Still an immune peptide

Selank has not forgotten its origins. In a 2014 study in Molecular Immunology, Kolomin and colleagues examined how Selank changes the expression of inflammation-related genes over time, building on earlier findings that Selank and its fragments altered the activity of immune genes in the mouse spleen (PMID: 24291245). That dual profile, brain and immune, is one of Selank’s most distinctive features.

Our Selank research guide goes deeper into its history.

Semax vs Selank: The Differences That Matter

With both stories told, the comparison becomes clear.

Parent molecule

Semax comes from ACTH, a pituitary hormone. Selank comes from tuftsin, an immune peptide. Both carry the same PGP tail.

Main research focus

Semax research centres on neurotrophic factors, especially BDNF, and on attention, learning, memory and recovery after stroke. Selank research centres on the GABA system, anxiety-related behaviour and immune regulation.

Proposed mechanism

Research indicates Semax works largely by increasing BDNF and nerve growth factor and activating their receptors, supporting neuron survival and plasticity. Research indicates Selank influences the expression of GABA-related genes and modulates immune and inflammatory gene activity.

Overall character

In broad terms, Semax is studied as an activating, neuroprotective compound, and Selank as a calming, balancing one. That contrast is exactly why they are so often studied together.

Regulatory attention

Both are registered medicines in Russia and research materials in the UK. Semax also drew attention in July 2026, when a US FDA advisory committee voted 8 to 5 to recommend adding it to the list of substances US compounding pharmacies may use, having reviewed it for cerebral ischaemia, migraine and trigeminal neuralgia. The recommendation is advisory and does not affect its UK status. Our article on the FDA advisory panel vote explains the details.

Why Study Them Together?

Complementary effects

Because Semax is associated with neurotrophic support and attention, and Selank with calming GABA-related effects, combining them allows researchers to explore how a neuroprotective signal and an anxiety-modulating signal interact. The pairing reflects a common research interest in how stress, anxiety and cognitive performance influence one another.

A shared design

Because both carry the same PGP tail and come from the same programme, they share similar stability characteristics, making them practical to study side by side.

The blend

Crown Peptides supplies both together as the Semax 5mg + Selank 5mg (Blend), and our article Semax and Selank: the two-peptide stack explores the combination in detail.

Where Stress, Attention and Immunity Meet

One reason the Semax and Selank pairing attracts so much research interest is that the systems they touch are deeply connected in the body.

The stress axis links them

ACTH, the parent of Semax, is the central hormone of the stress response, driving cortisol release from the adrenal glands. Long-term stress is known in research to reduce BDNF in the hippocampus and to affect attention, learning and mood. A compound derived from ACTH that raises BDNF without driving cortisol therefore sits at an interesting point in the stress system.

The immune system talks to the brain

At the same time, immune signals influence the brain. Inflammatory messengers produced during illness can change mood, motivation and cognition, a phenomenon researchers call sickness behaviour, and the relationship between inflammation and anxiety is an active research field. Selank, derived from an immune peptide and shown to alter both inflammation-related genes and GABA-related genes, sits right at that interface.

Why that makes the pair useful

Put together, the two peptides give researchers one tool rooted in the stress hormone system and focused on neurotrophic support, and another rooted in the immune system and focused on calming signals. Studying them separately and in combination allows questions about how stress, immunity, anxiety and cognitive performance interact, questions that are hard to approach with any single compound.

A Timeline of the Two Peptides

The history of Semax and Selank spans more than five decades. ACTH fragment research began in the 1960s with de Wied’s work in Utrecht. Tuftsin was discovered at Tufts University in 1970. Through the 1980s and 1990s, the Institute of Molecular Genetics in Moscow developed Semax, which was registered for medical use in Russia and became widely studied in stroke. Selank followed, developed from tuftsin with the same PGP strategy and later registered in Russia for anxiety-related use. Since the 2000s, both have been the subject of detailed molecular studies, from BDNF measurements in the hippocampus to whole-genome RNA sequencing after experimental stroke and gene panels covering the GABA system. In 2026, Semax reached a new audience when a US FDA advisory committee recommended it for wider pharmacy access.

Designing Research With Semax and Selank

The four-arm design

The clearest way to study the pair is to compare four conditions: control, Semax alone, Selank alone and both together. That separates each peptide’s contribution and shows whether the combination behaves differently from either alone. Because both are available individually as well as in the blend, all four arms can be built from matched material.

Choose readouts for each mechanism

For Semax, BDNF and nerve growth factor levels, TrkB activation and learning or attention tasks are the most closely linked measures. For Selank, GABA-related gene expression, anxiety-related behaviour and immune or inflammatory markers fit best.

Mind the timing

The gene expression studies found rapid changes within one to three hours, and the pattern shifted between time points. Sampling at more than one time point gives a much fuller picture of each peptide’s effects.

Consider the route

Both peptides have been widely studied by intranasal application in animal research, a route that may allow access to the brain. The route chosen can influence which effects are seen and how quickly.

The Technical Breakdown: Two Peptides, One Tail

This section goes into the structural detail for readers who want it.

The sequences side by side

Semax: Met-Glu-His-Phe-Pro-Gly-Pro. Selank: Thr-Lys-Pro-Arg-Pro-Gly-Pro. The first four residues of each carry the active signal; the Pro-Gly-Pro tail provides stability. Semax’s molecular weight is about 813; Selank’s about 751.

Why proline protects

Proline’s side chain loops back and bonds to its own backbone nitrogen, making it rigid and removing the hydrogen that most peptide bonds carry. Many peptidases cannot easily cleave bonds next to proline, so proline-rich sequences such as PGP resist breakdown. Glycine between the prolines adds flexibility, allowing the tail to adopt shapes that further hinder enzymes.

The HFRW connection in Semax

ACTH and the melanocortin hormones share a core sequence, His-Phe-Arg-Trp, that binds melanocortin receptors. Semax contains only part of that region, His-Phe, followed by the PGP tail, which helps explain why it retains brain-related effects without acting like ACTH on the adrenal glands.

Tuftsin and its receptor

Tuftsin binds receptors on phagocytic immune cells, and later research linked it to neuropilin-1, a receptor with roles in both the immune and nervous systems. That dual location offers one possible explanation for why a tuftsin-based peptide such as Selank shows both immune and brain-related effects.

PGP’s own activity

Proline-glycine-proline is not entirely inert. PGP and related sequences occur naturally as breakdown products of collagen and have their own reported biological activities, including effects on immune cells and blood clotting. Part of both peptides’ research interest lies in how their active fragments and the PGP tail work together.

Why Quality Control Matters for Short Proline-Rich Peptides

Semax and Selank are both seven residues long, with three prolines each. Proline-rich sequences can be challenging to synthesise cleanly, because coupling onto proline is slower than onto most other amino acids, which raises the risk of deletion impurities missing a single residue. A deletion in a seven-amino-acid peptide is a substantial change. Semax’s methionine is also vulnerable to oxidation, producing a sulfoxide that adds 16 to its mass and may alter its activity.

For the blend, both peptides must be present at their stated amounts and identified separately in analysis.

The Crown Peptides standard

Every batch of Semax, Selank and the Semax 5mg + Selank 5mg (Blend) supplied by Crown Peptides comes with a batch-specific certificate of analysis showing HPLC purity and mass spectrometry identity confirmation, with lot numbers matching those on vial labels. Published certificates are on our Lab Reports page, and our guides to peptide testing and reading a certificate of analysis explain the methods.

Handling

Both are supplied as lyophilised powders and should be stored cold, dry and away from light, with particular care to limit air exposure for Semax because of its methionine. Our guides to peptide reconstitution, how long peptides last and the peptide calculator cover the practical side, and Bacteriostatic Water is available alongside.

Related Compounds in Neurocognitive Research

Pinealon

Pinealon, a three-amino-acid peptide from the Saint Petersburg bioregulator programme, is studied for neuron protection through a proposed direct route into the cell nucleus, a useful contrast with Semax’s neurotrophic mechanism. See our Pinealon guide.

DSIP and Epitalon

DSIP is studied for sleep and stress hormone regulation, making it a natural neighbour to Selank’s calming research, and Epitalon for pineal and circadian biology.

Oxytocin

Oxytocin is a neuropeptide studied for social behaviour and stress responses, another angle on the brain systems Selank research touches.

Browse the full range in our neurocognitive research peptides category.

Semax and Selank Questions, Answered

What is the difference between Semax and Selank?

Semax is based on a fragment of the hormone ACTH and is studied mainly for BDNF, attention, learning and stroke recovery. Selank is based on the immune peptide tuftsin and is studied mainly for GABA-related effects, anxiety-related behaviour and immune regulation.

Why do both end in Pro-Gly-Pro?

Because both were designed by the same Moscow team, who added the proline-glycine-proline tail to protect the active fragments from rapid breakdown.

Does Semax affect cortisol like ACTH?

No. Semax uses only a short ACTH fragment that research has linked to brain effects, without ACTH’s hormonal action on the adrenal glands.

Is Selank a benzodiazepine?

No. Clinical studies in Russia described effects resembling benzodiazepines, and gene expression research found overlap with GABA’s effects, but Selank is a peptide with a different structure and route of action.

Which one is studied for stroke?

Semax. It has been studied extensively in stroke in Russia, including a 2018 study in which it increased plasma BDNF and was associated with faster functional recovery during rehabilitation, and laboratory work showing it helps compensate for gene expression changes caused by experimental stroke in rats.

Which one is studied for immune effects?

Selank, reflecting its origin in the immune peptide tuftsin. Research has shown it alters the activity of inflammation-related genes, alongside its effects on GABA-related genes in the brain.

Are Semax and Selank legal in the UK?

Neither is a controlled drug in the UK, and both are available as research materials. See are peptides legal in the UK for the full picture.

Same Workshop, Different Tools

Semax and Selank are a lovely example of how one good design idea can produce two very different research tools. The Moscow team took a fragment of a stress hormone and a fragment of an immune peptide, gave each the same protective proline tail, and ended up with one compound that raises the brain’s growth factors and another that tunes its calming system. One has been studied helping stroke patients recover; the other reshaping GABA-related gene activity and immune signalling.

Studied alone, each answers its own questions. Studied together, they open up the space where attention, anxiety and resilience meet. Explore Semax, Selank and the Semax 5mg + Selank 5mg (Blend) from Crown Peptides, every batch HPLC and mass spectrometry verified and dispatched from the UK.