Selective Growth Hormone Releasing Peptide
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) first described by Raun et al. in 1998. Developed by Novo Nordisk, it was designed to address the selectivity limitations of earlier GH secretagogues like GHRP-6 and GHRP-2, which stimulate GH release but simultaneously elevate cortisol, prolactin, and appetite. Ipamorelin achieves this selectivity by binding the ghrelin receptor (GHS-R1a) on anterior pituitary somatotrophs with a binding profile that triggers GH release without activating the downstream pathways responsible for cortisol and prolactin secretion. This pharmacological selectivity makes Ipamorelin the cleanest GH secretagogue available for research. It produces robust growth hormone pulses that mimic physiological GH secretion patterns — amplitude increases with minimal distortion of pulse frequency or baseline GH levels. The absence of cortisol elevation is particularly significant for long-term research protocols, as chronic cortisol elevation leads to muscle catabolism, immune suppression, and metabolic disruption that would confound GH research endpoints. Ipamorelin has been studied in over 20 published preclinical and clinical studies. A notable phase 2 clinical trial evaluated Ipamorelin for post-operative bowel recovery following abdominal surgery, where it demonstrated accelerated return of bowel function — an effect attributed to GH-mediated tissue repair rather than direct GI motility modulation.
The most selective GHRP available — stimulates GH release without elevating cortisol, prolactin, or appetite at standard doses.
Produces GH pulses that mirror natural secretion patterns — increased amplitude without disrupting baseline or frequency.
Unlike GHRP-6, does not activate ghrelin's orexigenic pathways — enabling GH research without confounding hunger variables.
GH-mediated effects on lean mass, fat oxidation, and body composition without cortisol-driven catabolism.
GH secretion during sleep is amplified, with observed improvements in slow-wave sleep duration and quality.
Combining with CJC-1295 (no DAC) produces amplified GH pulses — GHRH primes the pituitary, Ipamorelin triggers release.
Ipamorelin activates the growth hormone secretagogue receptor type 1a (GHS-R1a), the endogenous receptor for ghrelin, located on somatotroph cells in the anterior pituitary gland. Upon binding, Ipamorelin triggers a Gq/11 signaling cascade that activates phospholipase C (PLC), generating inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 releases calcium from intracellular stores, which triggers growth hormone vesicle exocytosis. The selectivity of Ipamorelin is attributed to its specific binding conformation at the GHS-R1a receptor. While GHRP-6 and GHRP-2 bind the receptor in a manner that also activates adrenocorticotroph and lactotroph cells (leading to cortisol and prolactin release), Ipamorelin's five-amino-acid structure engages only the somatotroph-specific activation domain. This produces a dose-dependent GH response with a clear ceiling effect — increasing the dose above ~300 mcg does not proportionally increase GH output, preventing supraphysiological GH spikes. The GH released by Ipamorelin subsequently activates the GH receptor (GHR) on hepatocytes, stimulating production of insulin-like growth factor 1 (IGF-1). The GH-IGF-1 axis then drives downstream anabolic effects including protein synthesis, lipolysis, and bone mineralization. When combined with GHRH analogs like CJC-1295 (no DAC), the GH response is synergistically amplified — GHRH primes somatotrophs by increasing GH mRNA transcription and vesicle loading, while Ipamorelin triggers the release of this increased GH pool.
Gold-standard GHRP for studying isolated GH effects without cortisol, prolactin, or appetite confounders.
ActiveGH-mediated lean mass preservation and fat oxidation research using clean GH stimulation.
ActivePhase 2 clinical trial demonstrated accelerated bowel function recovery following abdominal surgery.
Phase 2 CompleteStudying the relationship between GH secretion and slow-wave sleep quality and duration.
PreclinicalCombination protocols with CJC-1295 (no DAC) to study amplified pulsatile GH release.
ActiveStudying restoration of youthful GH pulsatility in somatopause models without metabolic side effects.
Preclinical| Period | Dose | Frequency | Notes |
|---|---|---|---|
| 1–4 | 200 mcg | 2–3× daily (SC) | Standard research dose — timing: morning, post-exercise, and/or pre-sleep |
| 5–8 | 200–300 mcg | 2–3× daily (SC) | May increase per dose — assess GH response |
| 9–12+ | 200–300 mcg | 2–3× daily (SC) | Maintenance — protocols typically run 8–16 weeks |
Ipamorelin is the most selective GHRP — it stimulates GH release without elevating cortisol, prolactin, or significantly increasing appetite. GHRP-6 is the least selective (strong hunger, cortisol, prolactin increase). GHRP-2 is intermediate (highest raw GH output but with moderate cortisol/prolactin). If the research objective requires clean GH axis stimulation without metabolic confounders, Ipamorelin is the preferred choice.
The combination of Ipamorelin + CJC-1295 (no DAC, also called Mod GRF 1-29) is one of the most studied GH-axis protocols. GHRH (CJC-1295) primes the pituitary by increasing GH mRNA and vesicle loading, while Ipamorelin triggers the release. This produces a synergistically amplified GH pulse greater than either peptide alone. Standard combined dosing: 100 mcg CJC-1295 no-DAC + 200 mcg Ipamorelin, administered simultaneously.
Research protocols typically administer 200–300 mcg 2–3 times daily. The most common timing is: morning (fasted), post-exercise, and before sleep. Pre-sleep administration capitalizes on the natural nocturnal GH surge. Doses should be taken on an empty stomach (at least 2 hours post-meal) since insulin and blood glucose blunt GH response. Avoid high-fat meals within 1 hour of dosing.
Ipamorelin produces peak GH levels approximately 30–40 minutes after subcutaneous injection, with the GH pulse returning to baseline within 2–3 hours (reflecting the ~2 hour half-life). The acute GH response is immediate from the first dose, but downstream effects on body composition, sleep, and IGF-1 levels develop over 4–8 weeks of consistent use.
Ipamorelin works through the body's own GH axis — it triggers release of the pituitary's own GH stores rather than providing exogenous GH. This is fundamentally different from synthetic GH (HGH) administration, which suppresses endogenous production through negative feedback. Ipamorelin amplifies physiological GH pulsatility, and research suggests the pituitary's capacity to produce GH is maintained during use.
Need help choosing a peptide?
Try the AI Coach →