Growth Hormone-Releasing Peptides (GHRPs)
The peptide supplements used for growth hormone augmentation are Growth Hormone-Releasing Peptides (GHRPs), specifically GHRP-6, GHRP-2, and Hexarelin, which are synthetic hexapeptides that selectively stimulate GH secretion.
Specific GHRP Formulations
The most studied GHRPs include:
- GHRP-6 (His-DTrp-Ala-Trp-DPhe-Lys-NH2): The original synthetic hexapeptide that demonstrated potent GH-releasing activity 1, 2
- GHRP-2: A modified version with similar efficacy that stimulates GH secretion even in patients with mutated GHRH receptors 3
- Hexarelin (His-D-2Me-Trp-Ala-Trp-D-Phe-Lys-NH2): A chemically more stable analog where tryptophan is substituted with 2-Methyl-Trp 4
Mechanism and Clinical Effects
These peptides work through specific receptors distinct from the GHRH pathway. GHRP-2 can stimulate GH secretion independently of GHRH signaling, as demonstrated in patients with homozygous GHRH receptor mutations who still showed a 4.5-fold increase in serum GH after GHRP-2 administration 3. This confirms direct action on pituitary somatotroph cells.
When administered intravenously, GHRPs produce:
- Peak GH levels within 10 minutes
- Dose-dependent responses (mean peak GH of 68.7 μg/L at 1.0 μg/kg dose) 2
- Selective GH stimulation without affecting LH, FSH, or TSH 1
- Synergistic effects when combined with GHRH 2
Oral administration is also effective: oral GHRP at 300 μg/kg produces comparable GH responses to 1 μg/kg IV, though with slower onset 5.
Important Clinical Context
These peptides are research tools, not FDA-approved treatments for adult GHD. The only FDA-approved long-acting GH formulation for adults with GHD is somapacitan (SOGROYA), approved in August 2020 6. This is actual recombinant human GH with albumin-binding technology, not a peptide secretagogue.
For legitimate adult GHD treatment, standard recombinant human GH replacement (daily injections at 200-300 μg/day for ages 30-60) or somapacitan (once-weekly) are the guideline-recommended therapies 7, 6.