Ipamorelin
NNC 26-0161, Ipa
The most selective growth hormone secretagogue - it raises GH with minimal spillover into cortisol or prolactin, which is what separates it from older ghrelin mimetics.
Preclinical only
Not approved. Development was discontinued after early-phase work. Added to the FDA's Category 2 bulk drug substances list, so compounding pharmacies may no longer produce it.
What it is
Ipamorelin is a pentapeptide that agonises the growth hormone secretagogue receptor (GHS-R) - the ghrelin receptor. It mimics ghrelin's effect on GH release without ghrelin's other effects, and that selectivity is the entire point of the molecule.
Earlier secretagogues in this family raised GH but dragged cortisol and prolactin up with them. Ipamorelin was designed to avoid that, and the original characterisation work showed GH release with little effect on ACTH, cortisol or prolactin at effective doses.
Why it is paired with CJC-1295
GH release is governed by two independent levers, and the peptides map onto them cleanly:
- GHRH receptor - the accelerator. CJC-1295 and tesamorelin act here.
- GHS-R / ghrelin receptor - a separate amplifier that also suppresses somatostatin, the brake. Ipamorelin acts here.
Hitting both produces a larger GH pulse than either alone. That is the pharmacological logic behind the ubiquitous CJC-1295 + ipamorelin stack, and the logic is sound even though the combination has never been trialled for body composition in healthy adults.
The evidence position
Ipamorelin reliably raises GH in humans - that part is established. What has never been demonstrated is that raising GH this way, in healthy adults, produces the downstream outcomes people take it for: muscle gain, fat loss, recovery, or better sleep. Clinical development was discontinued; a trial in post-operative ileus did not succeed.
So: a real, characterised pharmacological effect, with an unproven link to the outcomes that motivate its use.
Practical notes
- Fasted matters. Eat near the injection and the insulin spike blunts the GH pulse. Roughly two hours clear on either side is the usual convention.
- The 200-300 mcg ceiling is real. Above the saturation point you get more side effects, not more GH.
- Night dosing stacks with the natural pulse, which is the largest of the day and occurs in early slow-wave sleep.
- It makes you hungry. A ghrelin agonist during a fat-loss phase is working against you on the intake side, which is worth planning around.
Side effects and warning signs
Commonly reported
- Head rush or flushing in the minutes after injection
- Vivid dreams and deeper, sometimes disrupted sleep
- Transient hunger - it is a ghrelin receptor agonist, and ghrelin is the hunger hormone
- Water retention and mild joint aches at sustained use
- Injection-site irritation
Stop and get medical help
- Numbness or tingling in the hands - carpal tunnel from fluid retention is the classic GH-axis warning
- Rising fasting glucose
- Any active malignancy - raising GH and IGF-1 is contraindicated
Sources
From the community
Discussion for this compound concentrates in r/Peptidesource, r/PeptideForum and r/Biohackers.
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