Ipamorelin
| Category | Growth Hormone Secretagogues |
| Goals | Muscle & Performance · Recovery · Sleep |
| Evidence level | Preclinical for body-composition claims (mechanistic/early human data; no efficacy RCTs) |
| Legal status | Research-only — not approved for human use |
| FDA status | Not approved; pharmaceutical development discontinued |
| Half-life | Short (~2 h); GH peak ~0.67 h after dosing |
| Routes | Subcutaneous |
| CAS / MW / Sequence | 170851-70-4 · 711.9 g/mol · Aib-His-D-2-Nal-D-Phe-Lys-NH₂ (pentapeptide) |
| Last reviewed | 2026-06-07 |
In one line
A selective synthetic pentapeptide GHRP (ghrelin-receptor agonist) that triggers a clean pulse of growth hormone with minimal effect on cortisol or prolactin — the “gentle” GHRP, usually paired with CJC-1295.
Evidence at a glance
Ipamorelin’s selectivity for GH release is well characterized in animal and early human pharmacology, but there are no controlled human trials showing muscle, fat-loss, or recovery benefits, and its pharmaceutical development was discontinued. See Evidence Grading Explained and the Disclaimer.
Key Takeaways
- A selective GHS-R1a (ghrelin receptor) agonist — the first GHRP described as releasing GH without significant ACTH, cortisol, or prolactin elevation.
- Acts through a different pathway than GHRH analogs like CJC-1295, which is why the two are combined for a larger GH pulse.
- Considered the “gentle” GHRP versus older, less-selective agents like Hexarelin and GHRP-2/6.
- Human evidence is essentially mechanistic/PK — selectivity and GH-release kinetics; no efficacy outcome trials.
- Not FDA-approved; development halted. Most commonly stacked as CJC-1295 + Ipamorelin.
What Is It
Ipamorelin (developed by Novo Nordisk; code NNC 26-0161) is a synthetic pentapeptide with the sequence Aib-His-D-2-Nal-D-Phe-Lys-NH₂. It belongs to the growth-hormone-releasing peptide (GHRP) class and acts as a ghrelin mimetic at the growth-hormone secretagogue receptor (GHS-R1a). It was first described in 1998 as the first truly selective GH secretagogue, distinguishing it from earlier GHRPs that also raised stress and lactation hormones.
Mechanism of Action
- GHS-R1a (ghrelin-receptor) agonism (established mechanism) — binds the ghrelin receptor on pituitary somatotrophs and the hypothalamus, triggering a pulse of GH and downstream IGF-1.
- Hormonal selectivity (human/animal pharmacology) — releases GH without meaningful elevation of ACTH, cortisol, prolactin, FSH, LH, or TSH, even at doses far above the GH-releasing ED50 — the property that defines it.
- Synergy with GHRH (rationale for stacking) — combining a GHRP (Ipamorelin) with a GHRH analog (CJC-1295) produces a larger, complementary GH pulse than either alone.
Why "selective" matters
Older GHRPs (GHRP-2, GHRP-6, Hexarelin) can raise cortisol and prolactin and stimulate appetite strongly. Ipamorelin’s clean profile is the main reason it became the default GHRP in community stacks. See Side Effects & Risk Management.
Evidence by Outcome
| Outcome | Evidence | Notes |
|---|---|---|
| Releases GH (pulsatile) | Clinical | Demonstrated GH release in early human/animal pharmacology |
| Selectivity (no cortisol/prolactin rise) | Preclinical / Clinical | Hallmark finding; characterized vs other GHRPs |
| Muscle / lean-mass gain | Anecdotal | No human efficacy trials; extrapolated from GH biology |
| Fat loss / recomposition | Anecdotal | No controlled human data |
| Sleep / recovery | Anecdotal | Plausible via GH physiology; not directly studied |
| Bone / GI motility | Preclinical | Studied in animal models historically |
Reported Dosing
Not medical advice
Protocols as reported in community sources and non-clinical literature. There is no established human therapeutic dose. See Reconstitution & Dosing Math.
| Route | Dose (reported) | Frequency | Notes |
|---|---|---|---|
| Subcutaneous | ~100–300 µg per dose | 1–3× daily | Often pre-bed and/or post-workout; empty-stomach commonly described |
| With GHRH combo | ~100–300 µg + ~100 µg CJC-1295 (no-DAC) | per dose | The standard pairing |
Pharmacokinetics
A small peptide with a short half-life (~2 hours), Ipamorelin produces a GH peak roughly 40 minutes (~0.67 h) after subcutaneous injection followed by a rapid decline — consistent with the goal of mimicking a natural GH pulse. It is destroyed in the gut, so it is injectable (subcutaneous). Its short action is why multiple daily doses are described and why it is timed alongside the short-acting no-DAC CJC-1295. See Half-Life & Pharmacokinetics.
Side Effects & Risks
- Generally reported as well tolerated; common complaints are mild head-rush/flushing, injection-site reactions, and transient water retention.
- Less appetite stimulation than GHRP-6/ghrelin and less cortisol/prolactin effect than older GHRPs — the basis of its “gentle” reputation.
- Long-term human safety is unestablished; chronic GH/IGF-1 elevation carries the same general theoretical concerns (insulin sensitivity, tissue overgrowth) noted across the GH-secretagogue class.
- Sourcing risk: as a research chemical, identity and purity vary — verify before trusting a product. See Sourcing, Red Flags & Scams, Bloodwork & Monitoring, Side Effects & Risk Management.
Cycling
Community protocols commonly run Ipamorelin (usually with CJC-1295) in 8–12 week blocks with breaks. No evidence-based cycling standard exists. See Cycling.
Stacks It Appears In
- CJC-1295 + Ipamorelin — the canonical GHRP + GHRH pairing
- Sometimes combined with MK-677 for an oral + injectable GH-secretagogue approach
Comparisons
- vs Hexarelin — Hexarelin is a more potent but less selective GHRP (more cortisol/prolactin/appetite effect, faster desensitization).
- vs CJC-1295 — CJC-1295 is a GHRH analog (different receptor); they are complementary, not interchangeable.
- MK-677 vs Ipamorelin — MK-677 is an orally active ghrelin mimetic with a ~24 h half-life vs Ipamorelin’s short injectable pulse.
Sourcing & Quality
Sold as a lyophilized “research chemical,” so identity and purity are not guaranteed. Evaluate quality before trusting a product: How to Read a CoA, Sourcing, Red Flags & Scams. Reconstitution and storage: Reconstitution & Dosing Math, Storage & Handling. No vendors are endorsed here.
Legal & Regulatory Status
(As of 2026-06-05.) Not FDA-approved for human use; pharmaceutical development was discontinued and it is sold only as an unapproved research chemical. GH secretagogues, including GHRPs, are prohibited in and out of competition under the WADA Prohibited List (Section S2). Status varies by country. See Regulatory & Legal Status.
FAQ
Why is Ipamorelin called “selective”? It releases GH without significantly raising cortisol, prolactin, or ACTH, unlike older GHRPs — making it the cleaner-profile option.
Is Ipamorelin FDA-approved? No. It is unapproved and its clinical development was halted.
Does it build muscle in humans? There are no human efficacy trials. Evidence is limited to GH-release pharmacology; muscle claims are extrapolation.
Why combine it with CJC-1295? They act through different receptors (ghrelin vs GHRH) and together produce a larger GH pulse — see CJC-1295 + Ipamorelin.
References
- Raun K. et al. (1998). “Ipamorelin, the first selective growth hormone secretagogue.” European Journal of Endocrinology, 139(5):552–561.
- Ishida J. et al. (2020). “Growth hormone secretagogues: history, mechanism of action, and clinical development.” JCSM Rapid Communications.
- Gobburu J.V. et al. — pharmacokinetic characterization of ipamorelin GH-release kinetics in healthy subjects.
- WADA (2026). Prohibited List, Section S2 (peptide hormones, growth factors, related substances and mimetics).
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