Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| P21 (Cerebrolysin Analog) | Selank | |
|---|---|---|
| Category | Peptides | Peptides |
| Standard Dose | Research indicates 750 mcg-1 mg daily via intranasal administration or subcutaneous injection. | Research indicates 250-500 mcg daily via intranasal administration (0.15% solution, 2-3 drops per nostril). |
| Timing | Morning dosing preferred for cognitive effects. | Can be dosed morning through evening. Unlike Semax, Selank is calming and can be used at night. |
| Cycle Duration | 4-8 week cycles with 4-week rest periods. | 14-21 day cycles with equal rest periods. |
| Evidence Level | animal_plus_anecdotal | moderate_human |
P21 is a tetrapeptide (DGGL — Asp-Gly-Gly-Leu) derived from the most active region of ciliary neurotrophic factor (CNTF, residues 148-151), identified through reverse engineering of Cerebrolysin. An adamantylated glycine enhances BBB permeability and metabolic stability. P21 works through LIF/STAT3 pathway inhibition, BDNF/TrkB/CREB signaling enhancement, and restoration of synaptic proteins (synaptophysin, synapsin I) and glutamate receptors. It promotes neurogenesis and maturation of newborn neurons in the dentate gyrus.
Research indicates 750 mcg-1 mg daily via intranasal administration or subcutaneous injection.
Morning dosing preferred for cognitive effects.
4-8 week cycles with 4-week rest periods.
Selank (Thr-Lys-Pro-Arg-Pro-Gly-Pro) is a synthetic heptapeptide analog of the immunomodulatory peptide tuftsin (from IgG heavy chain) with a Pro-Gly-Pro extension for metabolic stability. It allosterically modulates GABA-A receptors, enhancing GABA binding and GABAergic neurotransmission. Selank modifies mRNA levels of 84 genes involved in GABAergic neurotransmission in the frontal cortex, enhances enkephalinase inhibition (increasing endogenous enkephalin levels), and modulates serotonergic and noradrenergic systems to produce anxiolytic and nootropic effects.
Research indicates 250-500 mcg daily via intranasal administration (0.15% solution, 2-3 drops per nostril).
Can be dosed morning through evening. Unlike Semax, Selank is calming and can be used at night.
14-21 day cycles with equal rest periods.
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