Growth Hormone Peptides Compared: Ipamorelin, CJC-1295, Sermorelin, MK-677 and More
The growth hormone secretagogue category includes GHRPs, GHRH analogues, and oral ghrelin mimetics — each with distinct receptor targets and GH release profiles. This research guide breaks down every major compound.
Growth hormone research peptides fall into two distinct pharmacological categories: GHRH analogues (which act on GHRH receptors to stimulate GH release) and GHRPs/ghrelin mimetics (which act on GHS-R1a receptors through a separate pathway). Understanding this distinction is foundational to GH research protocol design.
GHRH Analogues: Physiological GH Stimulation
Sermorelin (GHRH 1-29)
Sermorelin consists of the first 29 amino acids of endogenous GHRH — the minimum sequence that retains full biological activity at GHRH receptors. It produces physiological pulsatile GH release and is valuable for research on the GH axis itself, as it works through the natural pituitary pathway without receptor desensitization concerns.
MOD-GRF (1-29) / CJC-1295 without DAC
A modified GHRH fragment with four amino acid substitutions that confer DPP-4 resistance and improved receptor binding affinity. Half-life of approximately 30 minutes produces pulsatile GH release similar to endogenous patterns — ideal for research requiring physiological GH rhythms.
CJC-1295 with DAC
The Drug Affinity Complex technology covalently binds the peptide to serum albumin at Cys-modified residues, dramatically extending half-life to approximately 8 days. Single weekly dosing produces sustained GH and IGF-1 elevation — a fundamentally different pharmacokinetic profile than short-acting GHRH analogues. Useful for research on sustained GH axis stimulation.
Tesamorelin
A stabilized GHRH analogue with a trans-3-hexenoic acid modification. Extensively studied in visceral adiposity reduction, particularly in HIV-associated lipodystrophy models. Multiple Phase 3 trials provide a robust reference dataset.
GHRPs / Ghrelin Receptor Agonists
Ipamorelin
Ipamorelin is the most selective GHRP available. Unlike earlier compounds, it activates GHS-R1a without meaningful activity at ACTH, cortisol, or prolactin pathways. This selectivity makes it the cleanest GH secretagogue for research requiring isolated GH pathway stimulation. The pulsatile release profile mirrors physiological patterns.
GHRP-6
One of the original synthetic GHRPs and historically the most studied. GHRP-6 activates ghrelin receptor with strong GH release — but also stimulates appetite through central mechanisms. This dual property makes it relevant to combined GH and appetite/ghrelin research, though less selective than Ipamorelin.
GHRP-2
More potent than GHRP-6 with stronger GH pulse amplitude. Does produce modest cortisol and prolactin elevation — a factor to account for in research protocol design. Strong GH pulses make it valuable for body composition and recovery research models.
Hexarelin
The most potent synthetic GHRP available. Produces maximum GH release through GHS-R1a but has the least selectivity profile. Notably, hexarelin research has documented cardioprotective effects that appear independent of GH secretion — mediated through direct GHS-R1a activity in cardiac tissue. This makes hexarelin uniquely relevant to cardiovascular research protocols.
Oral GH Secretagogues
MK-677 (Ibutamoren)
The only oral GH secretagogue in this category. MK-677 is a non-peptide small molecule GHS-R1a agonist that achieves oral bioavailability due to its molecular structure. Daily oral dosing produces sustained IGF-1 elevation — documented in multiple peer-reviewed studies. Useful for research requiring oral administration or sustained rather than pulsatile GH axis stimulation.
IGF-1 Direct
IGF-1 LR3
IGF-1 LR3's N-terminal extension and Arg3 substitution reduce binding protein affinity by ~1000-fold, extending active half-life to approximately 20-30 hours. For downstream IGF-1 signaling research, LR3 provides sustained receptor activation that recombinant standard IGF-1 cannot achieve.
Combining GHRH and GHRP
A key principle in GH research: GHRH analogues and GHRPs act through separate, complementary mechanisms. Combining a GHRH analogue (like CJC-1295 no DAC) with a GHRP (like Ipamorelin) produces synergistic GH release — typically 2-5x greater than either compound alone. This combination is frequently used in research protocols examining maximal GH axis stimulation.
*For laboratory research purposes only. Not for human consumption.*