Neuropeptide Comparison · 2026
Semax vs. Selank: BDNF Focus vs. GABAergic Calm & Intranasal Protocols
Executive Brief
Developed at the Institute of Molecular Genetics of the Russian Academy of Sciences, Semax and Selank are seven-amino-acid synthetic regulatory peptides (heptapeptides) sharing an identical C-terminal `Pro-Gly-Pro` enzymatic shield. Semax is an ACTH(4–7) analog engineered for prefrontal executive drive, hippocampal BDNF/TrkB upregulation, and post-ischemic neuroprotection. Selank is an immunopeptide tuftsin analog engineered for non-sedating GABA-A anxiolysis, enkephalin preservation, and stress resilience without benzodiazepine tolerance.
ACTH(4–7)-PGP vs. Tuftsin-PGP
Semax vs. Selank: At-a-Glance Neurobiological Comparison (2026)
While both Semax and Selank are 7-amino-acid peptides delivered primarily via the olfactory/trigeminal intranasal pathway to bypass the blood-brain barrier within 2 to 4 minutes, their N-terminal tetrapeptide cores derive from two completely different endogenous physiological systems.
| Neurobiological Parameter | Semax (ACTH 4–10 Analog) | Selank (Tuftsin Analog) |
|---|---|---|
| Amino Acid Sequence & Mass | `Met-Glu-His-Phe-Pro-Gly-Pro` (7 AA; ~813.9 Da) | `Thr-Lys-Pro-Arg-Pro-Gly-Pro` (7 AA; ~751.9 Da) |
| Endogenous Parent Molecule | Adrenocorticotropic hormone fragment ACTH(4–7) + C-terminal PGP | Splenic IgG immunopeptide Tuftsin + C-terminal PGP |
| Primary Functional Role | Cognitive enhancer, executive attention, neuroprotection & BDNF upregulation | Non-sedating anxiolytic, stress resilience, GABA-A modulation & immunoregulation |
| Dominant Neurotransmitter Axis | BDNF/TrkB, NGF, Dopamine (D1/D2 striatal/prefrontal), Acetylcholine, Melanocortin MC4R | GABA-A allosteric receptor modulation, Leu-enkephalin preservation, Serotonin (5-HT) turnover |
| Hormonal / Adrenal Activity | Zero steroidogenic activity (does not stimulate adrenal cortisol release) | Zero steroidogenic activity; suppresses stress-induced catecholamine/IL-6 spikes |
| Sedation, Tolerance & Withdrawal | Mildly activating (can delay sleep if dosed late at night); no withdrawal | Zero sedation, zero amnesia, zero physical dependence or withdrawal (unlike benzodiazepines) |
| High-Potency Modified Variants | N-Acetyl Semax, N-Acetyl Semax Amidate (NASA), Adamax | N-Acetyl Selank, N-Acetyl Selank Amidate |
| Optimal Circadian Timing | Morning & early afternoon (200–600 mcg intranasal) | Anytime acute stress relief or afternoon/evening unwind (300–900 mcg intranasal) |
Peptide Architecture: Why Both Share the C-Terminal Pro-Gly-Pro (PGP) Shield
In the 1960s and 1970s, Dutch neuroscientist David de Wied discovered that short N-terminal fragments of adrenocorticotropic hormone—specifically ACTH(4–10) (`Met-Glu-His-Phe-Arg-Trp-Gly`) and ACTH(4–7) (`Met-Glu-His-Phe`)—retained all of ACTH's profound learning, memory, and attention-enhancing effects in the brain while completely lacking any steroidogenic activity on the adrenal cortex (zero cortisol spike). However, native ACTH(4–7) was degraded in human blood and nasal mucosa within 60 to 90 seconds by aminopeptidases and carboxypeptidases.
Researchers at the Institute of Molecular Genetics of the Russian Academy of Sciences (led by Academician Igor Ashmarin and Nikolai Myasoedov) solved this proteolytic instability by fusing the collagen-derived tripeptide sequence `Pro-Gly-Pro` (PGP) to the C-terminus of `Met-Glu-His-Phe`, creating Semax. Because proline's cyclic pyrrolidine ring resists cleavage by standard endopeptidases, adding `Pro-Gly-Pro` extended the neurobiological activity of a single intranasal dose to 20 to 24 hours—and when eventually cleaved, the released `PGP` glyproline tripeptide acts as an independent neuroprotective and cerebrovascular modulator in its own right.
Applying the exact same `Pro-Gly-Pro` stabilization platform to immunology and anxiety research, the team took tuftsin (`Thr-Lys-Pro-Arg`)—an endogenous 4-amino-acid immunomodulatory peptide cleaved from the Fc domain of immunoglobulin G (IgG) in the spleen that also exhibited anti-anxiety properties in behavioral models—and fused `Pro-Gly-Pro` to its C-terminus, creating Selank (`Thr-Lys-Pro-Arg-Pro-Gly-Pro`).
How They Work: Hippocampal BDNF/Dopamine Drive (Semax) vs. GABA-A/Enkephalin Calm (Selank)
Transcriptomic and neurochemical studies (Dolotov et al., 2006; Tsai, 2007; Volkova et al., 2016; Filatova et al., 2017) show that Semax and Selank regulate distinct, non-competing receptor networks in the central nervous system:
Semax's Four Neurobiological Mechanisms (Focus, Neuroplasticity & Neuroprotection):
- Rapid Hippocampal & Prefrontal BDNF / TrkB Upregulation: In published rat hippocampal and basal forebrain studies (Dolotov et al., Brain Research, 2006), a single intranasal administration of Semax increased Brain-Derived Neurotrophic Factor (BDNF) mRNA and protein levels by 1.4-fold to 3-fold within 3 to 24 hours, alongside a 2-fold increase in high-affinity TrkB receptor phosphorylation and Nerve Growth Factor (NGF) expression. This lowers the threshold for long-term potentiation (LTP) and synaptic remodeling during complex cognitive tasks.
- Potentiation of Striatal & Prefrontal Dopamine & Serotonin: Microdialysis studies (Eremin et al., 2005) demonstrate that while Semax alone does not cause an amphetamine-like basal dopamine dump (avoiding jitteriness or cardiovascular strain), it strongly amplifies evoked extracellular dopamine and serotonin release in the striatum and prefrontal cortex when the brain is actively engaged in goal-directed tasks.
- Melanocortin MC4R/MC5R Allosteric Modulation & Cholinergic Tone: Semax interacts allosterically with central melanocortin receptors and increases acetylcholinesterase-resistant cholinergic signaling in basal forebrain projection neurons, sharpening sustained visual and auditory attention under fatigue.
- Ischemic Stroke & Optic Nerve Neuroprotection: Approved in the Russian Federation for acute ischemic stroke (at higher 0.1% solution doses, 3–6 mg/day) and optic nerve atrophy, Semax suppresses glutamate excitotoxicity, nitric oxide overproduction, and microglial inflammatory cascades in hypoxic brain tissue.
Selank's Three Neurobiological Mechanisms (Anxiolysis, Enkephalins & Immunomodulation):
- Positive Allosteric Modulation of GABA-A Receptors: Radioligand binding and transcriptomic studies (Volkova et al., Frontiers in Pharmacology, 2016) revealed that Selank alters the affinity of endogenous GABA binding to GABA-A receptors and modulates the expression of 45 out of 84 neurotransmission-related genes in the frontal cortex within 1 hour—closely mirroring the gene-expression footprint of classical benzodiazepines (like medazepam or diazepam) while completely avoiding sedation, motor incoordination, cognitive blunting, or receptor downregulation.
- Inhibition of Enkephalin-Degrading Enzymes (Enkephalinase): Clinical biochemical studies in patients with generalized anxiety disorder (Zozulya et al., 2001; Kost et al., 2001) demonstrated that anxious individuals have abnormally rapid enzymatic breakdown of endogenous opioid pentapeptides (Leu-enkephalin and Met-enkephalin) in serum. Selank dose-dependently inhibits serum enkephalinases (IC50 ~10–20 µM), extending the half-life of endogenous enkephalins to restore natural emotional buffering against acute autonomic stress.
- Interleukin-6 (IL-6) & Th1/Th2 Cytokine Balancing: Retaining tuftsin's immunotropic heritage, Selank normalizes the balance of pro-inflammatory and anti-inflammatory cytokines—specifically suppressing elevated interleukin-6 (IL-6) in stressed or depressed subjects while stimulating type I interferon antiviral readiness (see our Peptide Therapy for Anxiety and Depression Guide).
Intranasal Olfactory Delivery
Base Peptides vs. N-Acetyl Amidate & Adamax Variants
Beyond unmodified base Semax and Selank, peptide chemists have developed N-terminally acetylated, C-terminally amidated, and adamantane-capped derivatives to further resist exopeptidase cleavage in the nasal mucosa and increase blood-brain barrier lipophilicity:
| Peptide Variant | Structural Modification | Subjective & Biochemical Profile |
|---|---|---|
| Base Semax / Base Selank | Unmodified heptapeptide (`MEHFPGP` / `TKPRPGP`) | Fastest onset (5–15 min intranasal), crisp 4–6 hour primary window; backed by all published human clinical trials |
| N-Acetyl Semax Amidate (NASA) | N-terminal acetyl cap + C-terminal `-NH2` amidation | ~30%–50% higher intranasal potency per mcg; smoother, longer 8–10 hour duration with less mid-afternoon drop-off |
| N-Acetyl Selank Amidate | N-terminal acetyl cap + C-terminal `-NH2` amidation | Extended 8–12 hour background anxiolytic calm; preferred in once-daily stress-resilience research protocols |
| Adamax | N-acetyl Semax with a C-terminal adamantyl (`Pro-Gly-Pro-Adamantane`) group | Highest lipophilicity and blood-brain barrier penetration; studied at lower 100–250 mcg intranasal doses (see our Adamax Peptide Guide) |
Intranasal Reconstitution, Spray Calibration Math & AM/PM Stacking
Why is intranasal administration the gold standard for Semax and Selank rather than subcutaneous injection? When sprayed onto the upper nasal turbinates, hydrophilic heptapeptides travel directly along the olfactory and trigeminal perineural channels into the cerebrospinal fluid and olfactory bulb within 2 to 4 minutes—achieving significantly higher central brain concentrations per milligram than subcutaneous injection (which exposes the peptide to systemic serum peptidases before reaching the brain).
Intranasal Spray Bottle Math (0.10 mL Metered Atomizer): A standard pharmaceutical metered nasal spray pump delivers exactly 0.10 mL (100 µL) per spray, meaning a 10 mL nasal bottle yields 100 sprays:
| Lyophilized Peptide Vial | Deionized / Sterile Saline Volume | Solution Concentration | Dose Per 0.10 mL Spray | Typical Research Dose |
|---|---|---|---|---|
| 10 mg Vial (0.1% Clinical Equivalent) | 10.0 mL (100 sprays) | 1.0 mg/mL (1,000 mcg/mL) | 100 mcg per spray | 2 to 4 sprays (200–400 mcg) |
| 10 mg Vial (Concentrated 5 mL) | 5.0 mL (50 sprays) | 2.0 mg/mL (2,000 mcg/mL) | 200 mcg per spray | 1 to 2 sprays (200–400 mcg) |
| 30 mg Vial (High-Strength 10 mL) | 10.0 mL (100 sprays) | 3.0 mg/mL (3,000 mcg/mL) | 300 mcg per spray | 1 to 2 sprays (300–600 mcg) |
The Classic Circadian “AM Semax + PM Selank” Research Stack: Because Semax and Selank act on non-overlapping pathways, researchers frequently pair them across the circadian cycle:
- Morning / Deep Work Block (Semax 200–400 mcg intranasal): Administered upon waking or 15 minutes before cognitively demanding analytical work to elevate prefrontal dopamine/acetylcholine tone and hippocampal BDNF expression.
- High-Pressure Meetings or Late Afternoon / Evening (Selank 300–600 mcg intranasal): Administered either alongside Semax when high-focus tasks carry performance anxiety (“calm focus”) or in the late afternoon to downregulate sympathetic stress, normalize cortisol/IL-6, and transition smoothly into evening recovery without sedation. Standard cycles run 10 to 14 consecutive days followed by a 1-to-2-week washout.
Frequently Asked Questions
What is the main difference between Semax and Selank?
Semax is a cognitive-enhancing heptapeptide derived from ACTH(4–7) that upregulates hippocampal BDNF/TrkB and potentiates prefrontal dopamine and acetylcholine for focus, memory, and neuroprotection. Selank is an anxiolytic and immunomodulatory heptapeptide derived from tuftsin that positively modulates GABA-A receptors and inhibits enkephalin breakdown to reduce anxiety without sedation.
Can Semax and Selank be stacked on the same day?
Yes. Because Semax acts on melanocortin, neurotrophin (BDNF), and catecholamine pathways while Selank acts on GABA-A and enkephalin pathways, they do not compete for the same receptors. Many research protocols pair Semax in the morning for executive focus with Selank in the afternoon or during high-stress cognitive tasks to smooth out sympathetic tension.
Does Selank cause sedation, brain fog, or withdrawal like benzodiazepines?
No. Published Phase 2/3 Russian clinical trials comparing Selank with medazepam and phenazepam in generalized anxiety disorder demonstrated that Selank achieves comparable anxiolytic relief without causing drowsiness, muscle relaxation, memory impairment, receptor tolerance, or discontinuation withdrawal syndrome.
Does Semax raise cortisol since it is derived from ACTH?
No. Full-length pituitary ACTH is 39 amino acids long and requires amino acids 11–24 to bind adrenal cortex MC2 receptors and stimulate cortisol synthesis. Semax contains only the 4-amino-acid behavioral core ACTH(4–7) attached to Pro-Gly-Pro, which has zero steroidogenic activity on the adrenal glands.
Why is intranasal spray preferred over subcutaneous injection for Semax and Selank?
Intranasal administration allows low-molecular-weight heptapeptides (~750–814 Da) to bypass the blood-brain barrier via the olfactory and trigeminal nerve sheaths, reaching the olfactory bulb and cerebrospinal fluid within 2 to 4 minutes while avoiding rapid degradation by peripheral plasma peptidases.
What is the difference between regular Semax/Selank and the N-Acetyl Amidate versions?
Adding an N-terminal acetyl group and a C-terminal amide cap protects both ends of the heptapeptide from aminopeptidase and carboxypeptidase enzymes in the nasal mucosa. Researchers report that N-Acetyl Semax Amidate (NASA) and N-Acetyl Selank Amidate provide a smoother, longer 8-to-12-hour duration of action at roughly 30% lower microgram doses compared with the unmodified base peptides.
Research Disclaimer
All content on this page is provided for informational and educational research purposes only based on published neurobiological and clinical literature. While Semax and Selank are approved medications in the Russian Federation, neither compound is approved by the US Food and Drug Administration (FDA), and both appear on the FDA 503A Category 2 bulk drug substances list. Nothing here constitutes medical advice, psychiatric diagnosis, or treatment recommendation.