ipamorelin

triggers your body's own GH pulse with less cortisol and prolactin baggage than older GHRPs. the clean one.

tier A · growth hormone · PCAC '24 503A excluded

verdict

the GHRP that doesn't move cortisol, prolactin, or ACTH at clinically relevant doses. selectivity is the whole pitch.

if you're asking why ipamorelin instead of GHRP-2 or GHRP-6 — selectivity. earlier GHRPs raise GH but also cortisol, prolactin, and ACTH at the doses needed for a meaningful GH bump. Raun 1998 nailed down ipamorelin's clean profile: at 200x the effective dose, no measurable change in cortisol, prolactin, FSH, LH, TSH, or ACTH. the ghrelin receptor is still the ghrelin receptor, so hunger can still hit, but it's usually milder than the older compounds.

if you're asking why it's almost always paired with CJC-1295 or sermorelin — different receptor. ipamorelin hits the ghrelin receptor via Gαq/11 signaling. CJC-1295 and sermorelin hit the GHRH receptor. stacking the two arms produces a bigger pulse than either alone, and the synergy is mechanistically clean. that's the entire architecture of modern clinic GH-axis protocols.

if you're asking about the regulatory ceiling — the pharmacology is unusually well-supported for a research peptide. multiple human phase 1 studies confirmed dose-response. what's missing is a completed phase 3, controlled long-term safety data, and FDA approval. the Oct 29, 2024 PCAC vote against 503A inclusion lowered the ceiling further. research-peptide vendors continue; compounding pharmacies do not.

based on published evidence and disclosed clinical practice. not medical advice.

why A-tier

a selective ghrelin receptor (GHS-R1a) agonist developed by Novo Nordisk in the late 1990s as a GH secretagogue. the breakthrough was selectivity: ipamorelin triggers GH release without spiking cortisol, prolactin, or ACTH, the side effects that plagued earlier GHRPs like GHRP-6 and hexarelin. pairs naturally with GHRH analogs (CJC-1295, sermorelin) because it activates a different receptor. the CJC+ipa blend is the single most common peptide clinic protocol in existence. A-tier based on clean mechanism, solid phase 1 data, and decades of consistent use, held back from S by absence of FDA approval or phase 3 efficacy program.

the core tension

On its own it's a clean, selective GH secretagogue. Novo Nordisk designed it specifically to avoid the cortisol and prolactin spikes that held back GHRP-2 and GHRP-6. Paired with CJC-1295, it became the backbone of peptide-medicine GH protocols. Pharma never packaged the combination because neither component is patentable as a blend, so peptide clinics built that protocol instead.

what it is

A synthetic pentapeptide that hits the ghrelin receptor (GHS-R1a) and nothing else. Five amino acids, three of them unnatural (aminoisobutyric acid, D-tryptophan). Novo Nordisk internal code NNC 26-0161. No FDA-approved product. Never reached commercial launch.

what it does

Triggers a pulse of growth hormone through Gαq/11 signaling on the pituitary. Different receptor from GHRH, which is why ipamorelin stacks cleanly with CJC-1295 or sermorelin. Effective dose is roughly 100-300 μg per injection. GH peaks around 60 minutes. The hallmark is what it doesn't do. At 200 times the effective dose, no measurable change in cortisol, prolactin, FSH, LH, TSH, or ACTH.

origin

Built at Novo Nordisk in the late 1990s. Raun et al. published the foundational paper in European Journal of Endocrinology in 1998. Helsinn Healthcare, via Sapphire Therapeutics, later took the program for postoperative ileus and ran phase 2 trials in the mid-2000s. The trials missed. Helsinn shelved it. The compound has lived in the research-peptide channel ever since.

why researchers are interested

Selectivity is the entire pitch. Earlier GHRPs (GHRP-6, GHRP-2, hexarelin) raised GH but also cortisol, prolactin, and ACTH at clinically relevant doses. Ipamorelin doesn't. Pairs with GHRH analogs to produce a larger pulse than either alone. Appetite effects are usually milder than the older GHRPs, but the ghrelin receptor is still the ghrelin receptor, so hunger can still hit. The CJC-1295 + ipamorelin blend is the workhorse of modern peptide-clinic GH protocols.

does it work

Yes on mechanism, same caveat as CJC-1295. The 1998 selectivity data has held up. Multiple human phase 1 studies confirmed dose-response. Newer literature (Andersen 2001, Greenwood-Van Meerveld 2016) supports the body-composition and GI-motility consequences of ghrelin-receptor activation. What's missing is a completed phase 3, controlled long-term safety data, FDA approval. The pharmacology is unusually well-supported for a research peptide. The trial economics for getting it formally approved as a standalone drug never made sense. The Oct 29, 2024 FDA PCAC voted against 503A inclusion, citing immunogenicity, peptide impurity, limited route-specific safety data, and serious adverse events in IV gastric-motility research. Compounding pharmacies lost the 503A pathway. Research-peptide vendors continue. A-tier on pharmacology, with the regulatory ceiling now lower.

claims vs the data

• stimulates growth hormone release — supported — Raun et al. 1998 established dose-dependent GH release in swine. followed by multiple human phase 1 studies.
• doesn't raise cortisol or prolactin — supported — selectivity established in the original 1998 paper. no cortisol, prolactin, FSH, LH, TSH, or ACTH changes at 200x effective GH-release dose.
• synergizes with CJC-1295 or sermorelin — supported — GHRH receptor + ghrelin receptor activation are mechanistically independent. the combination produces larger GH pulses than either alone. this is well-characterized pharmacology.
• safe for long-term use — unverified — phase 1 data clean. no long-term controlled trials. most chronic use is peptide clinic / gray market without systematic tracking.
• fda-approved — contradicted — ipamorelin never reached phase 3 for any indication. Helsinn-Sapphire developed it for postoperative ileus but abandoned program.
• better than HGH — partially true — preserves natural pulsatility, uses body's negative feedback, theoretically safer. effect size (absolute GH/IGF-1 elevation) is smaller than exogenous HGH.

key facts

• molecular formula: C₃₈H₄₉N₉O₅
• molecular weight: 711.85 g/mol
• amino acids: 5 (pentapeptide)
• half-life: ~2 hours
• type: selective ghrelin receptor agonist (GHS-R1a)
• CAS: 170851-70-4
• 5 aa pentapeptide
• 1998 first published (raun et al.)
• 0x cortisol/prolactin rise ("selective")
• ~2 hr half-life

frequently asked questions

What is ipamorelin?

Ipamorelin is a selective growth hormone secretagogue peptide, a synthetic pentapeptide that binds the ghrelin receptor (GHSR) and triggers pulsatile GH release. It is known for being the cleanest of the GHRP-class compounds, with minimal off-target effects on cortisol or prolactin.

What does ipamorelin do?

Ipamorelin stimulates natural pulsatile GH release with less cortisol and prolactin elevation than older GHRPs like GHRP-2 and GHRP-6. Community users report improved sleep, recovery, body composition changes, and skin quality over months of use. Clinical trials were conducted for other indications but did not progress to approval.

How is ipamorelin typically administered?

Ipamorelin has no FDA-approved dosing protocol for any human indication. Published research used controlled injection routes, and community CJC-1295 pairing is not the same thing as a validated fixed-blend trial package.

What are the side effects of ipamorelin?

Ipamorelin has a notably clean side effect profile versus older GHRPs. Appetite effects are usually milder than GHRP-2 or GHRP-6, but hunger can still occur because the receptor is the ghrelin receptor. Occasional users report mild injection-site reactions or transient flushing. At supraphysiological doses or with long-term use, general GH-related effects like fluid retention and joint aches can appear.

Is ipamorelin FDA approved?

No. Ipamorelin is not FDA-approved for any indication. It was investigated clinically in a postoperative-ileus program but did not achieve approval. It is sold as a research chemical and falls under WADA prohibited substances for competitive athletes.

How much does ipamorelin cost?

Ipamorelin is not a prescription drug and has no clinical retail price. On the research-chemical market it is inexpensive. Hormone clinics sometimes prescribe compounded ipamorelin/CJC-1295 blends as monthly packages.

related peptides

• cjc+ipa blend — the standard GH stack, both in one vial
• cjc-1295 — GHRH stacking partner
• sermorelin — GHRH analog, often stacked
• tesamorelin — FDA-approved GHRH analog
• hgh — what GHRH+GHRP stacks indirectly release

reptides grades the research record and cites the literature behind every call. research reference only; not medical advice.