Overview
Ipamorelin is a synthetic pentapeptide (5 amino acids: Aib-His-D-2-Nal-D-Phe-Lys-NH2) and a selective agonist of the ghrelin receptor (GHS-R1a, growth hormone secretagogue receptor type 1a). It was developed by Novo Nordisk in the late 1990s and is distinguished from earlier GHRP-class agents (GHRP-2, GHRP-6) by its high receptor selectivity — ipamorelin stimulates GH release from the pituitary without meaningfully increasing ACTH, cortisol, prolactin, or appetite, unlike its predecessors. This selectivity profile makes ipamorelin the preferred GHRP for GH optimization protocols in functional medicine, as it avoids the HPA-axis stimulation and appetite-stimulating side effects that limit the use of GHRP-2 and GHRP-6 in most patients. Ipamorelin is almost universally combined with a GHRH analog (typically CJC-1295 without DAC or sermorelin) to achieve synergistic GH pulse amplification via dual-pathway receptor activation.
Mechanism of Action
GHS-R1a (ghrelin receptor) agonism: Ipamorelin binds GHS-R1a on somatotroph cells, activating Gq/11 protein signaling, IP3-mediated calcium release, and PKC activation. This pathway is distinct from GHRH-receptor signaling (Gs/adenylate cyclase/cAMP), enabling synergistic GH release when both pathways are activated simultaneously (combination with CJC-1295 or sermorelin).
GH release selectivity: Ipamorelin's defining pharmacological characteristic is its selectivity for GH release over ACTH and cortisol. GHRP-2 and GHRP-6 cause meaningful cortisol elevation at standard doses; ipamorelin at up to 200mcg produces negligible ACTH/cortisol changes — a feature that preserves the beneficial stress-hormone balance and avoids sleep disruption or anxiety that some patients experience with GHRP-2.
Somatostatin-sensitive: Like CJC-1295, ipamorelin-stimulated GH release remains subject to somatostatin inhibition — preserving hypothalamic-pituitary negative feedback regulation. This distinguishes it from direct rhGH.
Appetite neutrality: Unlike ghrelin and GHRP-6, ipamorelin does not meaningfully activate orexigenic (appetite-stimulating) signaling — making it appropriate for patients managing weight or body composition.
Evidence Base
Pharmacokinetic / dose-finding studies: Bowers et al. (original GHRP-class research) and Raun et al. (Novo Nordisk group) established ipamorelin's pharmacology and GH selectivity. Animal studies confirm selective GH release without ACTH stimulation.
Post-operative GI recovery (human Phase II): A Novo Nordisk-sponsored Phase II trial assessed ipamorelin for post-operative GI ileus — found to accelerate GI motility recovery after abdominal surgery. Development was discontinued for commercial rather than safety reasons.
Body composition / functional GH optimization: No large published human RCTs. Most clinical use is extrapolated from rhGH and early GHRP data and from clinic-level IGF-1 tracking, rather than from large outcome trials. Body composition effects are qualitatively similar to but milder than rhGH given the secretagogue mechanism.
Combination with CJC-1295: The synergistic GH amplification with combined GHRHR + GHS-R1a stimulation is pharmacologically established and reported in human open-label protocols, with IGF-1 elevations of 40–60% commonly documented.
Dosing & Timing
| Protocol | Dose | Route | Frequency | Timing |
|---|---|---|---|---|
| Standard GH optimization | 100–300 mcg | SQ injection | Daily (bedtime) | Fasted 2+ hours; bedtime preferred |
| Combined with CJC-1295 without DAC | 100–200 mcg each | SQ injection | Daily at bedtime | Inject together (single syringe compatible) |
| Three-times-daily (advanced) | 100 mcg | SQ injection | 3×/day (morning, pre-workout, bedtime) | Fasted state for each dose. TID dosing reserved for short-term or advanced protocols; for long-term healthspan use, once-daily bedtime dosing is usually sufficient. |
Ipamorelin can be mixed in the same syringe with CJC-1295 without DAC for single-injection convenience; compatible in bacteriostatic water vehicle.
Forms & Bioavailability
Lyophilized powder for SQ reconstitution. Stable 28 days at 4°C after reconstitution. SQ injection. No oral bioavailability.
Regulatory: Ipamorelin appears on FDA compounding restriction lists (503A/503B) — same status as CJC-1295. Many "research peptide" products marketed outside pharmacy channels are not regulated for purity or potency. Verify current legal status before prescribing or procuring.
Safety & Side Effects
Most well-tolerated GHRP: Ipamorelin's selectivity profile results in the most favorable side effect profile among GHRP-class agents.
Common: Mild transient headache, facial flushing or tingling at injection; mild water retention at higher doses.
No significant cortisol elevation: Major clinical advantage over GHRP-2.
No significant appetite stimulation: Advantage over GHRP-6.
Glucose: Modest insulin resistance from GH elevation; monitor fasting glucose as with any GH-stimulating agent.
Cancer risk (theoretical): Elevated IGF-1 as mitogen; keep within normal range.
Drug & Supplement Interactions
| Agent | Interaction | Management |
|---|---|---|
| CJC-1295 without DAC / sermorelin | Synergistic via separate receptor pathways | Standard combination; amplified GH response |
| GHRP-2, GHRP-6 | Same receptor; no additional benefit from combining GHRP agents | Do not combine two GHRP agents |
| Somatostatin analogs | Antagonize ipamorelin at the GH secretion step | Avoid |
| Insulin | GH elevation antagonizes insulin; monitor glucose | Standard GH-insulin interaction |
Who Should Consider It
- Adults seeking GH axis optimization as part of a physician-supervised protocol
- Those who tried GHRP-2 or GHRP-6 and experienced cortisol-related side effects (anxiety, sleep disruption)
- Individuals wanting appetite-neutral GHRP for body composition protocols
Bottom Line
Ipamorelin is the GHRP of choice for most GH optimization applications — its selectivity for GH release over cortisol and appetite sets it apart from its predecessors and makes it the most clinically appropriate GHRP for the majority of patients. The CJC-1295 (without DAC) + ipamorelin combination, injected at bedtime in a fasted state, is the current standard protocol in functional medicine GH optimization. The evidence base, while pharmacologically well-characterized, does not include clinical outcome RCTs — a limitation shared with all GHS agents.
Last reviewed: 2026.