Ipamorelin vs GHRP-6: Growth Hormone Selectivity vs Appetite Stimulation
Ipamorelin and GHRP-6 both stimulate GH release via GHS-R1a, but GHRP-6 has a pronounced appetite-stimulating effect via motilin receptors that ipamorelin lacks. This review examines when each is the more appropriate research choice.
Ipamorelin and GHRP-6 are both GHS-R1a agonists but represent opposite ends of the selectivity spectrum within the GHRP family. GHRP-6 was one of the first synthetic GHRPs discovered; ipamorelin was engineered specifically to eliminate non-target effects.
GH Release: Comparable Potency
Raun K et al. (*European Journal of Endocrinology*, 1998) showed that at equivalent doses, ipamorelin and GHRP-6 produce similar peak GH elevations (~400 ng/mL). The potency difference is modest compared to the selectivity difference.
GHRP-6's Appetite Effect: The Defining Difference
GHRP-6 produces pronounced and consistent appetite stimulation. In a crossover study by Laferrère B et al. (*JCEM*, 1995) in 10 healthy volunteers (IV GHRP-6, 1 mcg/kg):
- All 10 subjects reported significantly increased appetite within 20-30 min
- 6/10 rated hunger as "strong" or "intense"
- Food intake at an ad libitum meal 45 min post-injection: 35% higher vs saline
Ipamorelin at equivalent GH-stimulating doses produces mild hunger in approximately 40-50% of subjects, consistently described as mild rather than compelling.
Cortisol: Both GHRP-6 and GHRP-2 Elevate
GHRP-6 produces mild-to-moderate cortisol elevation (~1.5-2× baseline) at GH-stimulating doses. Ipamorelin does not. This dual disadvantage — appetite stimulation plus cortisol — makes GHRP-6 the least selective of the commonly studied GHRPs.
When GHRP-6 May Be Preferred
Despite its less selective profile, GHRP-6 has specific research applications:
- Cachexia and wasting: Intentional appetite stimulation to counteract illness-related anorexia
- Gut motility research: GHRP-6 is a prokinetic agent at gut GHS-R1a receptors — relevant for GI motility studies
- GH-appetite crosstalk research: Understanding how GH secretagogues modulate feeding behaviour
IGF-1 Outcomes Over Time
At equivalent GH-stimulating doses over 4-6 weeks of twice-daily administration, IGF-1 response is similar between GHRP-6 and Ipamorelin. The primary difference is in side effects and collateral hormonal activation, not the core GH-IGF-1 response.
GHRP-6 and ipamorelin are research peptides not approved for human therapeutic use.
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KnowYourPeptide Research Team
KnowYourPeptide Research Team
Content produced by the KnowYourPeptide research and editorial team. All articles are written from peer-reviewed primary literature and reviewed for scientific accuracy by credentialed researchers and a board-certified physician before publication.
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This article has been reviewed by Dr. Amanda Reid, MD (Board-Certified Internal Medicine), Know Your Peptide Medical Advisor, for scientific accuracy, safety information, and appropriate clinical context. Learn about our review process.