Ipamorelin

Overview

Ipamorelin is a synthetic pentapeptide growth hormone secretagogue (GHS) developed in the mid-1990s by Novo Nordisk. It belongs to the growth hormone releasing peptide (GHRP) family and acts as a ghrelin mimetic, binding to the growth hormone secretagogue receptor (GHS-R1a) in the anterior pituitary to stimulate the release of endogenous growth hormone (GH).

What distinguishes Ipamorelin from earlier GHRPs such as GHRP-6 and GHRP-2 is its selectivity. Ipamorelin produces a dose-dependent GH release without significant elevations in cortisol, aldosterone, prolactin, or adrenocorticotropic hormone (ACTH) at therapeutic doses. This selectivity was demonstrated in pivotal studies by Raun et al. (1998), where Ipamorelin was shown to release GH with potency comparable to GHRP-6 but with a side-effect profile closer to that of growth hormone releasing hormone (GHRH).

Ipamorelin was initially investigated by Novo Nordisk for conditions related to growth hormone deficiency but was not advanced to regulatory approval as a pharmaceutical product. It has since become one of the most widely discussed peptides in the research and anti-aging communities, valued for its clean GH release profile.

Amino Acid Sequence

Ipamorelin is a pentapeptide with the following structure:

Aib-His-D-2-Nal-D-Phe-Lys-NH₂

• Molecular formula: C₃₈H₄₉N₉O₅
• Molecular weight: 711.85 g/mol
• CAS Number: 170851-70-4

Notable structural features include:

• Aib (alpha-aminoisobutyric acid) at position 1 — a non-standard amino acid that confers resistance to enzymatic degradation
• D-2-Nal (D-2-naphthylalanine) at position 3 — contributes to GHS-R binding affinity
• D-Phe (D-phenylalanine) at position 4 — D-amino acids enhance protease resistance
• C-terminal amidation — improves receptor binding and stability

Mechanism of Action

GHS-R1a Receptor Agonism

Ipamorelin binds to the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor targeted by the endogenous hormone ghrelin. Activation of this receptor on somatotroph cells in the anterior pituitary triggers:

• Release of stored growth hormone from secretory granules
• Amplification of the GH pulse amplitude without altering pulse frequency
• Preservation of normal pulsatile GH secretion patterns

Selective GH Release

Unlike GHRP-6, which activates GHS-R1a broadly and stimulates appetite, ACTH, cortisol, and prolactin, Ipamorelin demonstrates high selectivity for GH release. Studies by Raun et al. demonstrated that even at doses 200-fold above the effective GH-releasing dose, Ipamorelin did not significantly elevate ACTH or cortisol — a finding not replicated with any other GHRP.

Synergy with GHRH Analogs

Ipamorelin is frequently studied in combination with GHRH analogs such as CJC-1295 and Sermorelin. The mechanistic rationale is complementary pathway activation:

• GHRH analogs stimulate GH synthesis and priming of somatotroph cells
• Ipamorelin triggers the release of stored GH and suppresses somatostatin (the GH-inhibiting hormone)
• The combination produces a synergistic GH pulse greater than either agent alone

Somatostatin Suppression

Ipamorelin, like other GHRPs, functionally opposes somatostatin's inhibitory effect on GH release. This is mediated both directly (at the pituitary level) and indirectly (at the hypothalamic level through modulation of somatostatin-releasing neurons).

Research Summary

Pharmacokinetics

• Half-life: Approximately 2 hours
• Onset of action: GH elevation detectable within 15–20 minutes of subcutaneous administration
• Peak GH levels: Typically reached 30–45 minutes post-injection
• GH elevation duration: Approximately 2–3 hours before returning to baseline
• Route: Subcutaneous injection (primary); intravenous (research settings)
• Bioavailability: High subcutaneous bioavailability due to structural stability (D-amino acids and Aib residue)
• Metabolism: Hepatic and renal clearance; D-amino acid substitutions confer moderate protease resistance

The GH pulse induced by Ipamorelin mimics the amplitude and duration of natural endogenous GH pulses, which is considered advantageous over exogenous GH administration that produces supraphysiological, non-pulsatile levels.

Dosing Protocols

The following dosing information is compiled from published research and community discussion for educational purposes only.

Standard Protocol

Key Points

• Total daily dose: 200–600 mcg split into 2–3 injections
• Route: Subcutaneous
• Cycle length: 8–12 weeks on, 4–8 weeks off
• Best paired with: CJC-1295 (Mod GRF 1-29) at 100 mcg per injection for synergistic GH pulse
• Schedule: 5 days on, 2 days off to prevent receptor desensitization
• Timing matters: Must be taken on empty stomach — food (especially fats/carbs) blunts GH release

Common Discussion Topics

1. Ipamorelin + CJC-1295 combination — The most commonly discussed peptide pairing in the GH secretagogue space. The combination of a GHRP (Ipamorelin) with a GHRH analog (CJC-1295) is discussed for synergistic GH release.

2. Comparison with GHRP-6 and GHRP-2 — Ipamorelin's lack of appetite stimulation and cortisol/prolactin elevation is its primary advantage over GHRP-6 and GHRP-2.

3. Timing and dosing protocols — Discussion centers around pre-bed and post-training timing to coincide with natural GH pulse windows. Fasting state administration is generally recommended as food (particularly fats and carbohydrates) can blunt the GH response.

4. Desensitization — Whether chronic GHRP use leads to reduced receptor sensitivity is a commonly debated topic. Some protocols advocate for cycling or rest periods.

5. Anti-aging applications — Ipamorelin's clean GH release profile makes it popular in longevity-focused discussions, particularly for age-related GH decline.

6. Sleep quality — Anecdotal reports of improved deep sleep quality are commonly discussed, consistent with the known role of GH pulses during slow-wave sleep.

Related Compounds

• CJC-1295 — a GHRH analog frequently paired with Ipamorelin for synergistic GH release
• GHRP-6 — an earlier GHRP with stronger appetite stimulation and broader hormonal effects
• GHRP-2 — a potent GHRP with intermediate selectivity between GHRP-6 and Ipamorelin
• Sermorelin — a GHRH analog with FDA history; alternative GHRH component for combination protocols
• Hexarelin — the most potent GHRP by GH release magnitude, but with significant cortisol and prolactin elevation
• MK-677 (Ibutamoren) — an oral, non-peptide GHS-R1a agonist with a much longer half-life (~24 hours)