Ipamorelin vs GHRP-2 vs GHRP-6
A complete comparison of the three most-researched growth hormone releasing peptides — selectivity, GH pulse amplitude, side effect profiles, and stacking protocols.
Use code HEALTH for 20% off · COA-verified · Ships same day
Choose Ipamorelin if…
- ✓You need selective GH release without cortisol or prolactin co-stimulation
- ✓Research cycle is 12–16 weeks (long-term safety profile)
- ✓Stacking with CJC-1295 for the gold-standard GHRH+GHRP protocol
- ✓Lean body composition is the primary research endpoint
Choose GHRP-2 if…
- ✓Maximum GH pulse amplitude is the primary research endpoint
- ✓Short-term (4–8 week) research protocol where cortisol elevation is acceptable
- ✓Studying GH secretagogue dose-response relationships
- ✓Comparing GHRP potency across compounds
Choose GHRP-6 if…
- ✓Appetite stimulation or orexigenic pathway research is the goal
- ✓Studying ghrelin receptor biology and hunger signaling
- ✓Recovery research where increased caloric intake is beneficial
- ✓Budget-sensitive protocols (GHRP-6 is typically lowest cost)
Research use only. Compound Review scores vendors on documentation — laboratory certificates, lot records, pricing and company identity. Nothing on this page is guidance on human or veterinary use, dosing or health outcomes.
What Are Growth Hormone Releasing Peptides (GHRPs)?
Growth hormone releasing peptides (GHRPs) are synthetic peptides that stimulate pituitary GH secretion by binding the ghrelin receptor (GHS-R1a). Unlike GHRH analogues — which mimic the hypothalamic signal that tells the pituitary to release GH — GHRPs act through a separate receptor pathway, making them synergistic with GHRH analogues when stacked. Ipamorelin, GHRP-2, and GHRP-6 are the three most extensively studied GHRPs in preclinical and clinical research.
The key distinction between the three compounds is selectivity. GHS-R1a is expressed not only in the pituitary (where GH release occurs) but also in the hypothalamus, adrenal glands, and gut. Compounds that bind GHS-R1a with high affinity across all tissues produce off-target effects: cortisol and ACTH release from the adrenal axis, prolactin elevation, and appetite stimulation via hypothalamic and gut ghrelin pathways. Ipamorelin was specifically engineered to minimize these off-target effects while preserving GH-stimulating potency.
Pathway Comparison Diagram
Ipamorelin selectively activates GHS-R1a with no cortisol or prolactin elevation; GHRP-2 adds cortisol/prolactin side effects; GHRP-6 adds strong appetite stimulation via ghrelin.
Full Comparison: Ipamorelin vs GHRP-2 vs GHRP-6
| Parameter | Ipamorelin | GHRP-2 | GHRP-6 |
|---|---|---|---|
| Compound Class | GHRP / GHS-R1a agonist | GHRP / GHS-R1a agonist | GHRP / GHS-R1a agonist |
| Amino Acids | 5 (pentapeptide) | 6 (hexapeptide) | 6 (hexapeptide) |
| Half-Life | ~2 hours | ~1–2 hours | ~1–2 hours |
| GH Pulse Amplitude | Moderate (3–7× baseline) | High (7–15× baseline) | Moderate (3–6× baseline) |
| GH Selectivity | High — GH only | Low — GH + cortisol + prolactin | Moderate — GH + mild cortisol |
| Cortisol Elevation | Minimal | Significant (+50–100%) | Mild–moderate |
| Prolactin Elevation | Minimal | Significant | Mild |
| Appetite Stimulation | Minimal | Mild | Pronounced (ghrelin-mediated) |
| IGF-1 Elevation | Moderate | High | Moderate |
| Best Stack Partner | CJC-1295 (gold standard) | CJC-1295 (max GH output) | CJC-1295 (less studied) |
| Research Cycle Length | 8–16 weeks | 4–8 weeks (cortisol concern) | 8–12 weeks |
| Best For | Long-term GH optimization, lean mass | Short-term max GH pulse research | Appetite stimulation, recovery |
The Selectivity Difference: Why It Matters
The most clinically significant difference between these three GHRPs is their selectivity for GH release versus co-stimulation of cortisol, prolactin, and appetite pathways. This distinction was the primary engineering goal when ipamorelin was developed — researchers at Novo Nordisk specifically designed it to dissociate GH-stimulating activity from the adrenal and appetite side effects seen with earlier GHRPs like GHRP-2 and GHRP-6.
Ipamorelin
High Selectivity
GHRP-2
Low Selectivity
GHRP-6
Moderate Selectivity
The cortisol co-stimulation of GHRP-2 is particularly relevant for research focused on body composition. Cortisol is catabolic — it promotes muscle protein breakdown and fat storage, directly opposing the anabolic effects of elevated GH and IGF-1. Research cycles using GHRP-2 therefore carry an inherent hormonal tension that ipamorelin avoids entirely.
Clinical Evidence Summary
| Compound | Key Finding | Notable Limitation |
|---|---|---|
| Ipamorelin | Dose-dependent GH release without cortisol or prolactin co-stimulation in animal pharmacology (Raun 1998, PMID 9849822); the human programme was discontinued and its data are not in the indexed literature we hold | No indexed human RCT; preclinical and unpublished early-phase work only |
| GHRP-2 | Strongest GH pulse amplitude of the three (7–15× baseline); significant IGF-1 elevation in GH-deficient adults; used as a GH stimulation test agent | Consistent cortisol and prolactin co-stimulation limits long-term research utility |
| GHRP-6 | Reliable GH stimulation; pronounced appetite stimulation via ghrelin pathway confirmed in multiple studies; used in cachexia and appetite research | Hunger side effects limit compliance in body composition research; less studied than GHRP-2 for GH endpoints |
Research Dosing Protocols
| Protocol | Ipamorelin | GHRP-2 | GHRP-6 |
|---|---|---|---|
| Frequency | 2–3× daily | 2–3× daily | 2–3× daily |
| Route | SubQ injection | SubQ injection | SubQ injection |
| Timing | Fasted (2+ hr post-meal) | Fasted (2+ hr post-meal) | Fasted (2+ hr post-meal) |
| Cycle Length | 8–16 weeks | 4–8 weeks | 8–12 weeks |
Decision Matrix
| Research Criterion | Ipamorelin | GHRP-2 | GHRP-6 |
|---|---|---|---|
| Selective GH release (no cortisol) | |||
| Maximum GH pulse amplitude | |||
| Long research cycles (12–16 wk) | |||
| Lean body composition focus | |||
| Appetite stimulation research | |||
| GHRH analogue stacking | |||
| Minimal hormonal side effects | |||
| Short-term GH max output |
Favorable Partial Unfavorable
What the cited studies used
One row per compound: the amount and schedule administered in a specific indexed study, who received it, and the paper. These are reports of what was done in that study, not recommendations, and several are animal or single-dose studies. Where no indexed human regimen exists we say so rather than print a number. Community "stacks" and cycle schedules are not reproduced on this site.
Research use only. Compound Review scores vendors on documentation — laboratory certificates, lot records, pricing and company identity. Nothing on this page is guidance on human or veterinary use, dosing or health outcomes.
| Compound | Regimen in the study | Population | Source |
|---|---|---|---|
| Ipamorelin | No human dose-ranging trial in our reference set The 1998 paper characterises GH release in animals and in vitro; the human development programme was discontinued and its dosing is not in the indexed literature we hold. | Rat and pig pharmacology (Raun 1998; Johansen 1999) | PMID 9849822 Raun et al., Eur J Endocrinol 1998 |
| GHRP-2 | No cited trial in our reference set GHRP-2 has been used as a diagnostic GH-stimulation agent in the literature; we have not verified a PMID for a dosing study and print none. | — | none |
| GHRP-6 | No cited trial in our reference set Same standard as GHRP-2: without a verified PMID we print no amount. | — | none |
| CJC-1295 (with DAC) | Single subcutaneous doses of 30, 60, 90 or 125 µg/kg; repeated 30 or 60 µg/kg weekly or every two weeks This is the DAC form with a multi-day half-life, not 'CJC-1295 no DAC' (mod GRF 1-29), for which we hold no human dose trial. | Healthy adults (two randomised, placebo-controlled studies) | PMID 16352683 Teichman et al., J Clin Endocrinol Metab 2006 |
Side Effect Profiles
| Side Effect | Ipamorelin | GHRP-2 | GHRP-6 |
|---|---|---|---|
| Injection site reaction | Mild | Mild | Mild |
| Headache (post-injection) | Occasional | Occasional | Occasional |
| Flushing / warmth | Mild | Moderate | Mild |
| Cortisol elevation | None | Significant | Mild–moderate |
| Prolactin elevation | None | Significant | Mild |
| Appetite stimulation | Minimal | Mild | Pronounced |
| Water retention | Mild | Moderate | Mild |
| Fatigue / lethargy | Rare | Occasional | Rare |
Frequently Asked Questions
What is the main difference between Ipamorelin, GHRP-2, and GHRP-6?
All three are growth hormone secretagogues (GHS) that bind the ghrelin receptor (GHS-R1a) to stimulate pituitary GH release, but they differ critically in selectivity and side effect profiles. Ipamorelin is the most selective: it stimulates GH release without meaningfully elevating cortisol, prolactin, or ACTH. GHRP-2 produces strong GH pulses but also significantly elevates cortisol and prolactin. GHRP-6 produces moderate GH pulses with the most pronounced appetite stimulation and the highest ghrelin-mediated hunger side effects of the three.
Which GHRP produces the most GH?
GHRP-2 produces the largest GH pulse amplitude of the three, with studies demonstrating GH elevations 7–15× above baseline in dose-dependent fashion. Ipamorelin produces moderate but highly selective GH pulses (3–7× baseline), and GHRP-6 produces pulses broadly similar to ipamorelin but with greater inter-individual variability. For raw GH output, GHRP-2 leads — but at the cost of cortisol and prolactin co-stimulation.
Is Ipamorelin better than GHRP-2?
For most research applications, ipamorelin is considered superior to GHRP-2 due to its selectivity profile. Ipamorelin produces GH release without the cortisol, prolactin, or ACTH co-stimulation seen with GHRP-2. Elevated cortisol is catabolic and counteracts the anabolic goals of GH stimulation. GHRP-2 may be preferred in short-term research contexts where maximum GH pulse amplitude is the primary endpoint and hormonal side effects are acceptable.
Why does GHRP-6 cause hunger?
GHRP-6 stimulates the ghrelin receptor (GHS-R1a) with high potency and also has significant activity at the ghrelin receptor in the hypothalamus and gut, triggering the orexigenic (appetite-stimulating) pathway. This results in pronounced hunger, particularly in the 30–60 minutes following injection. Ipamorelin and GHRP-2 also bind GHS-R1a but with different receptor kinetics that produce less pronounced appetite stimulation — ipamorelin in particular has the lowest hunger side effect burden of the three.
Can Ipamorelin, GHRP-2, and GHRP-6 be stacked with GHRH analogues?
Yes — combining a GHRP with a GHRH analogue produces synergistic GH release through complementary receptor pathways. The most studied combination is CJC-1295 + ipamorelin, which is considered the gold standard GHRH+GHRP stack. GHRP-2 + CJC-1295 produces higher peak GH but with cortisol co-elevation. GHRP-6 + CJC-1295 is less commonly studied. For research stacking protocols, ipamorelin is the preferred GHRP partner due to its selectivity.
What is the best GHRP for fat loss?
GHRP-2 produces the highest GH pulse amplitude, which drives the greatest lipolytic (fat-mobilizing) response through IGF-1 and direct GH receptor activation on adipocytes. However, its cortisol co-stimulation can partially offset fat loss benefits. Ipamorelin's selective GH stimulation without cortisol elevation may produce a more favorable net body composition effect over longer research cycles. GHRP-6's appetite stimulation makes it the least favorable for fat loss research.
Source Research-Grade GHRPs
Purgo Labs supplies COA-verified Ipamorelin, GHRP-2, and GHRP-6 for research purposes.
Shop at Purgo Labs — Use Code HEALTH for 20% Off