Ipamorelin: The Selective GH Secretagogue Fitness Forums Prefer to GHRP-6

Ipamorelin is a five-amino-acid growth hormone-releasing peptide (GHRP) Novo Nordisk published in 1998. It hits the same ghrelin receptor as GHRP-6, but in swine it did not raise ACTH or cortisol the way GHRP-2 and GHRP-6 did. It is not recombinant GH, and there is no FDA-approved ipamorelin product.

TL;DR

• Sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH2. Raun’s group cut the central Ala-Trp of GHRP-1 and still kept GHRP-like GH release.
• Selectivity claim: in conscious swine, ACTH and cortisol stayed at GHRH-like levels even at doses more than 200-fold the GH ED50.
• Human PK: 15-minute IV infusions in healthy men. Terminal half-life about 2 hours. Peak GH at 0.67 hours, then a single pulse that fell away.
• Drug attempt: a 2014 postoperative-ileus trial (0.03 mg/kg IV twice daily) was well tolerated and missed its meal-tolerance endpoint (p = 0.15).
• Not a licensed GH drug. WADA names ipamorelin under S2.2.4. A catalog vial is not a prescription.

Educational only. Not medical advice, not a protocol, and not a reason to treat a research vial as growth hormone.

What is ipamorelin actually?

Ipamorelin is a pentapeptide: Aib-His-D-2-Nal-D-Phe-Lys-NH2.

Raun and colleagues at Novo Nordisk pulled it out of a chemistry series that dropped the central Ala-Trp dipeptide of GHRP-1. In primary rat pituitary cells it released GH with an EC50 of 1.3 nmol/L, next to 2.2 nmol/L for GHRP-6. Antagonist work showed a GHRP-like receptor, not the GHRH receptor (Raun et al., 1998).

That receptor is now called GHS-R1a, the ghrelin receptor. Binding on somatotrophs and hypothalamic neurons opens a phospholipase C and calcium path that dumps a GH pulse.

GHRH analogs such as sermorelin and CJC-1295 use a different receptor. That is why boards pair ipamorelin with a GHRH analog. Two keys, one pituitary.

For the size primer, see Peptides 101.

Why did they call it the first selective GHS?

First-generation GHRPs work. They also leak.

In conscious swine, GHRP-6 and GHRP-2 raised ACTH and cortisol. Ipamorelin did not, even at doses more than 200-fold its GH ED50 of 2.3 nmol/kg. FSH, LH, prolactin, and TSH did not move for any of the secretagogues tested (Raun et al., 1998).

The paper’s punchline is specific. Ipamorelin was the first GHRP-receptor agonist with GH selectivity similar to GHRH. That is a swine endocrine profile, not a human body-composition trial.

Fitness forums translated it as “the clean GHRP.” The animal contrast with GHRP-6 is real. Human head-to-head cortisol data of the same design are not.

What did the human volunteer study measure?

Gobburu, Agerso, Jusko, and Ynddal ran a dose-escalation PK/PD study in healthy men. Five 15-minute IV rates: 4.21, 14.02, 42.13, 84.27, and 140.45 nmol/kg, eight subjects each (Gobburu et al., 1999).

PK was dose-proportional. GH came as one episode, then fell to negligible levels. Inter-person spread was larger for the GH response than for the peptide’s own clearance.

That is a short IV pulse study, not a gym protocol. It does show the peptide is active in humans and that the GH pulse is brief.

Did ipamorelin ever become a drug?

Novo Nordisk framed it as a clinical candidate. The human study that later ran was not a muscle trial.

Beck’s Ipamorelin 201 group tested 0.03 mg/kg IV twice daily versus placebo in adults after small or large bowel resection. 117 enrolled, 114 in the safety and modified intent-to-treat sets.

Median time to a standardized solid meal was 25.3 hours versus 32.6 hours (p = 0.15). Adverse-event rates were 87.5% on drug and 94.8% on placebo. The authors called it well tolerated and not significantly different on the key efficacy analyses (Beck et al., 2014).

There is no FDA-approved ipamorelin label. Licensed GH-axis products, when they exist, live in pharmacy and telehealth channels. That is what the provider directory and price index compare.

How does it compare with other secretagogues?

A practical map for the fitness audience, based on published pharmacology, not forum dose charts:

The Ipamorelin versus CJC-1295 explainer covers the two-receptor stack. This article is the ipamorelin half.

What about bone and muscle in animals?

Svensson gave adult female rats ipamorelin, GHRP-6, or GH by minipump for 12 weeks. DXA bone mineral content rose. pQCT, Archimedes volume, and ash weight showed bigger bones, not a higher volumetric density (Svensson et al., 2000).

Andersen put ipamorelin next to methylprednisolone in 8-month-old female rats for 3 months. Combined GH secretagogue plus glucocorticoid raised calf tetanic tension and periosteal bone formation rate about four-fold versus glucocorticoid alone (Andersen et al., 2001).

Those are rat infusion and injection studies. They are not hypertrophy RCTs in trained humans.

Is a research vial the same as a GH prescription?

No.

Recombinant GH is a licensed protein drug. Ipamorelin is a short GHRP that asks the pituitary to pulse. WADA lists it by name under S2.2.4 growth hormone secretagogues, prohibited at all times, alongside anamorelin, ibutamoren (MK-677), and ghrelin itself (WADA Prohibited List).

A catalog vial is a research chemical. Identity, salt, and purity are COA questions.

Handling education lives on the reconstitution guide and the calculator. There are no large randomized trials of ipamorelin for muscle gain, fat loss, or recovery in healthy adults.

Bottom line: Ipamorelin is a real, short GHRP with swine data showing GHRH-like ACTH/cortisol sparing, a 1999 human IV pulse study, and a 2014 ileus trial that missed. It is not GH in a smaller bottle, and a research vial is not an FDA-approved secretagogue drug.

Educational only. Not medical advice. Not a recommendation to use ipamorelin, GHRP-6, hexarelin, CJC-1295, sermorelin, or any research-grade growth hormone secretagogue.