What Is Ipamorelin
Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) developed by Novo Nordisk in Denmark and first described in published literature in 1998. It acts as a selective agonist of the ghrelin receptor (GHS-R1a), stimulating growth hormone release from pituitary somatotroph cells.
Ipamorelin is not naturally occurring. Its five-amino-acid sequence includes non-natural residues — alpha-aminoisobutyric acid (Aib) at the N-terminus and D-configured phenylalanine and 2-naphthylalanine — which provide metabolic stability and receptor specificity. At approximately 711.9 Da as the free base, it is one of the smaller peptides in common research use.
Why “Selective” Matters
Ipamorelin was the first growth hormone secretagogue described as “selective” — a distinction that defines its research value. Here's what that means in practice:
| Hormone | GHRP-6 | GHRP-2 | Ipamorelin |
|---|---|---|---|
| Growth Hormone | Strong increase | Strong increase | Strong increase |
| Cortisol | Significant increase | Moderate increase | Minimal / none |
| Prolactin | Significant increase | Moderate increase | Minimal / none |
| ACTH | Increase | Increase | Minimal / none |
All three compounds bind the same ghrelin receptor (GHS-R1a). The selectivity difference comes from which receptor-coupled signaling pathways are preferentially activated by each compound's binding conformation. Ipamorelin produces potent GH release while avoiding the cortisol and prolactin spikes seen with earlier GHRPs.
Mechanism of Action
Ghrelin Receptor Agonism
Ipamorelin activates GHS-R1a on pituitary somatotrophs, triggering intracellular calcium mobilization and GH release. This pathway is distinct from and additive with the GHRH pathway (which operates through cAMP-dependent signaling), which is why ipamorelin is often combined with GHRH analogs like CJC-1295.
Pulsatile GH Release
With a terminal half-life of approximately 2 hours — measured after intravenous infusion in healthy adult males; no subcutaneous human pharmacokinetic data has been published — ipamorelin produces discrete GH pulses rather than sustained elevation. Those studies showed dose-proportional GH responses.
The CJC-1295 + Ipamorelin Combination
The most common research protocol pairs ipamorelin (a GHRP acting through the ghrelin receptor) with CJC-1295 without DAC (a GHRH analog acting through the GHRH receptor). Because they operate through different receptor pathways, the combination produces an additive GH response greater than either compound alone.
Research Evidence
Limitations
- Human clinical data is limited to PK/PD studies. No large efficacy trials have been completed for any indication.
- Clinical development stopped at Phase 2. Postoperative ileus was the most advanced program, run by Helsinn after acquiring the asset from Novo Nordisk via Sapphire Therapeutics. Two Phase 2 trials completed: one missed its primary endpoint (median time to first tolerated meal 25.3 vs 32.6 hours, p=0.15) and the second, a 320-patient trial finishing in 2014, never reported results. No Phase 3 trial has ever been run.
- “Selective” does not mean “side-effect free.” Selectivity refers specifically to the cortisol/prolactin/ACTH profile relative to earlier GHRPs. Other potential effects of sustained GH axis stimulation remain relevant.
- Long-term safety data does not exist.
- Ipamorelin is not FDA-approved for any medical use.
Purity and Lab Testing
HPLC Purity
Research-grade ipamorelin should test at 98% or above. At only 5 amino acids, it is relatively straightforward to synthesize at high purity.
Mass Spectrometry
The expected molecular weight is approximately 711.9 Da for the free base. Mass spec confirms identity and distinguishes ipamorelin from other GHRPs (GHRP-6 at ~873 Da, GHRP-2 at ~818 Da, both free base). Material supplied as an acetate salt weighs more, so check which form a COA reports.
For a complete guide to evaluating COAs, see How to Read a Peptide COA.
Summary
Ipamorelin is a synthetic pentapeptide (~711.9 Da) that stimulates GH release through the ghrelin receptor without the cortisol and prolactin increases seen with GHRP-6 and GHRP-2. That selectivity, demonstrated in swine in 1998, is its defining characteristic. It is commonly combined with CJC-1295 without DAC for an additive GH response through two different receptor pathways. Human data is limited to pharmacokinetic studies; no large efficacy trials exist. It is not FDA-approved.