Ipamorelin

An unapproved growth-hormone-releasing peptide (GHRP)

Not FDA-approved · not available for sale or prescription

Stylised model of the real sequence

Overview.

Ipamorelin was never approved as a drug; its Phase 2 human trials for postoperative ileus failed to show sufficient efficacy. It is a synthetic five-amino-acid ghrelin-receptor agonist developed by Novo Nordisk to release growth hormone with less effect on cortisol, ACTH and prolactin than older GHRPs. It is currently sold in the US only as an unapproved research chemical.

Also known as NNC 26-0161

The molecule, decoded.

Sequence: Aib-His-D-2-Nal-D-Phe-Lys-NH2 (Aib = 2-aminoisobutyric acid)
Length: 5 residues
Molecular weight: 711.9 g/mol
Formula: C38H49N9O5
CAS number: 170851-70-4
Half-life: ~2 hours (not well established)
Routes studied: intravenous (postoperative ileus trials), subcutaneous (unapproved research-chemical use; no published human safety data)
Modifications: N-terminal Aib; D-2-naphthylalanine and D-Phe residues; C-terminal amide -- all confer protease resistance and receptor selectivity

How it works.

Binds the ghrelin receptor (GHS-R1a) on pituitary somatotrophs and hypothalamic neurons, activating Gq/phospholipase-C/IP3-calcium signaling that triggers GH release. Early comparative pharmacology reported greater selectivity for the GH axis, with less cortisol/ACTH/prolactin co-release than GHRP-2, GHRP-6 or hexarelin at pharmacologically active doses.

Evidence · Early or small human studies

What the research shows

phase 2 RCT2014

In a Phase 2, multicenter, double-blind, placebo-controlled proof-of-concept trial (117 enrolled, 114 treated), IV ipamorelin after bowel resection did not significantly shorten time to first tolerated meal (median 25.3 vs 32.6 h, p=0.15) or improve secondary endpoints.

adults undergoing open or laparoscopic bowel resection

Source

FDA safety review2023

FDA's Category 2 safety summary cites the Phase 2 IV postoperative-ileus trial, in which two ipamorelin-treated patients died of postoperative complications (causality unclear) and hypokalemia and hyperglycemia were more frequent than with placebo; FDA also cites immunogenicity risk.

adults after bowel resection (Phase 2 postoperative-ileus trial)

Source

development history2014

Clinical development (Helsinn Therapeutics) for postoperative ileus was discontinued after the Phase 2 program failed to demonstrate sufficient efficacy; ipamorelin was never advanced to an approved indication.

postoperative bowel-resection patients

animal and cell study1998

In rat pituitary cells, anaesthetised rats and conscious swine, ipamorelin released GH with potency similar to GHRP-6 but, unlike GHRP-2 and GHRP-6, did not raise ACTH or cortisol even at doses >200x the GH ED50 (none of the secretagogues tested changed prolactin, FSH, LH or TSH).

rat pituitary cells, anaesthetised rats and conscious swine

Source

What to know first.

Based on: trials (Phase 2 ileus data) plus an FDA safety review; no chronic-use human safety data.

Reported side effects

in the Phase 2 IV trial: hypokalemia, hyperglycemia, insomnia, nausea, vomiting and abdominal distention (per FDA review); overall adverse-event rates were similar to placebo (87.5% vs 94.8%)
two deaths among ipamorelin-treated post-surgical patients (anastomotic-leak complications; causality unclear), cited by FDA
no published human safety data for subcutaneous use

Cautions

FDA-cited immunogenicity concern for injectable/nasal formulations
not established as safe for IV use outside controlled trials
class-wide insulin-sensitivity/glucose concerns shared with other GH secretagogues

Checked 2026-09

Where it stands.

Not FDA-approved · not available for sale or prescription. Ipamorelin is not FDA-approved and is not available for sale or prescription. We profile it because people ask about it.

FDA: not approved; investigational only (discontinued after Phase 2 for postoperative ileus).
Compounding: Ipamorelin acetate (only the acetate; the free base was never listed) was placed in Category 2 under both 503A and 503B on September 29, 2023. The 503A nomination was withdrawn and FDA removed it from 503A Category 2 effective September 27, 2024; it remains in 503B Category 2 (outsourcing facilities) as of FDA's April 22, 2026 update, citing immunogenicity risk and serious adverse events including death with IV use. On October 29, 2024 the Pharmacy Compounding Advisory Committee voted 0 yes, 12 no, 1 abstain against adding ipamorelin acetate and, separately, ipamorelin free base to the 503A Bulks List. It is not eligible for 503A compounding (not on the bulks list, no USP monograph, not in an approved drug).
Sport (WADA): Prohibited at all times under S2 (Growth Hormone Secretagogues and their mimetics) of the WADA Prohibited List, naming ipamorelin explicitly.
Enforcement: FDA Category 2 'significant safety risk' listing (ipamorelin acetate), Sept 29, 2023: removed for 503A on Sept 27, 2024 after the nomination was withdrawn; still in effect for 503B outsourcing facilities per fda.gov (updated Apr 22, 2026)
FDA Pharmacy Compounding Advisory Committee voted 0-12 (1 abstention) on Oct 29, 2024 against adding ipamorelin acetate or free base to the 503A Bulks List
FDA warning letter to Tailor Made Compounding (Apr 1, 2020) cited compounding with ipamorelin; the pharmacy pleaded guilty (E.D. Ky., Oct 2020) to distributing unapproved new drugs including ipamorelin
Named in industry litigation over FDA's Category 2 process alongside CJC-1295, AOD-9604 and thymosin alpha-1 (2026, per The FDA Law Blog)

References (3)

Ipamorelin

Overview.

The molecule, decoded.

How it works.

What the research shows

What to know first.

Reported side effects

Cautions

Where it stands.

More in Growth