Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| GHK (without copper) | P21 (Cerebrolysin Analog) | |
|---|---|---|
| Category | Peptides | Peptides |
| Standard Dose | Research indicates 1-3% concentration in topical formulations. Injectable dosing follows GHK-Cu protocols at 1-2 mg daily. | Research indicates 750 mcg-1 mg daily via intranasal administration or subcutaneous injection. |
| Timing | Topical application morning and evening. Injectable in evening. | Morning dosing preferred for cognitive effects. |
| Cycle Duration | Topical use can be ongoing indefinitely. Injectable cycles 8-12 weeks. | 4-8 week cycles with 4-week rest periods. |
| Evidence Level | moderate_human | animal_plus_anecdotal |
GHK (glycyl-L-histidyl-L-lysine) is a naturally occurring tripeptide found in human plasma, saliva, and urine that has an extremely high affinity for copper(II) ions. Even without exogenously complexed copper, GHK rapidly chelates available copper in biological systems, making copper-free GHK functionally similar to GHK-Cu in vivo. The peptide stimulates collagen and glycosaminoglycan synthesis, modulates metalloproteinase activity, resets gene expression patterns toward a healthier state (affecting 31.2% of human genes), and activates wound healing cascades.
Research indicates 1-3% concentration in topical formulations. Injectable dosing follows GHK-Cu protocols at 1-2 mg daily.
Topical application morning and evening. Injectable in evening.
Topical use can be ongoing indefinitely. Injectable cycles 8-12 weeks.
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.
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