Side-by-side comparison of mechanisms, dosing, interactions, and stacking potential.
| GHRP-6 | P21 (Cerebrolysin Analog) | |
|---|---|---|
| Category | Peptides | Peptides |
| Standard Dose | Research indicates 100-300 mcg administered 1-3 times daily via subcutaneous injection. | Research indicates 750 mcg-1 mg daily via intranasal administration or subcutaneous injection. |
| Timing | On empty stomach, 30+ minutes before meals. Bedtime dose most important. The strong hunger effect makes pre-meal timing practical. | Morning dosing preferred for cognitive effects. |
| Cycle Duration | 8-16 week cycles. | 4-8 week cycles with 4-week rest periods. |
| Evidence Level | moderate_human | animal_plus_anecdotal |
GHRP-6 (Growth Hormone Releasing Peptide-6) is a synthetic hexapeptide that stimulates GH release through activation of the growth hormone secretagogue receptor (GHS-R1a/ghrelin receptor) on pituitary somatotrophs. It acts via dual sites — pituitary and hypothalamic — possibly involving regulatory factors beyond GHRH and somatostatin. GHRP-6 also stimulates ghrelin-mediated appetite signaling, increases cortisol and prolactin release, and has demonstrated cytoprotective properties including cardioprotection.
Research indicates 100-300 mcg administered 1-3 times daily via subcutaneous injection.
On empty stomach, 30+ minutes before meals. Bedtime dose most important. The strong hunger effect makes pre-meal timing practical.
8-16 week cycles.
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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