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Ipamorelin

Also known as NNC 26-0161, Ipamorelin acetate

Selective ghrelin receptor agonist (GHRP) that releases growth hormone without raising cortisol or prolactin.

early-clinical Growth hormone research chemical

At a glance

Category
Growth hormone
Status
research chemical
Route
subcutaneous (intravenous in study settings)
Half-life
a short terminal half-life of 2 hours, measured in eight healthy male subjects per dose level after 15-minute intravenous infusions in the phase 1 PK/PD study 2. No subcutaneous half-life has been published
Onset
GH peak within 15-60 minutes; change in body composition only after weeks to months
Molecular weight
711.9 g/mol
Sequence
Aib-His-D-2-Nal-D-Phe-Lys-NH2 (pentapeptide with non-natural amino acids; cannot be written in standard 1-letter code)

Developed by Novo Nordisk; clinical development discontinued after phase 2 (postoperative ileus). There is no approved ipamorelin medicine in the US or the EU. Its regulatory status in the US is that of a compounding bulk substance: on 29 September 2023 the FDA placed ipamorelin acetate in category 2 under its 503B interim policy — bulk substances that may present significant safety risks — citing a risk of immunogenicity from aggregation and peptide-related impurities, the characterisation difficulty created by its unnatural amino acids, and a published study reporting serious adverse events including death when ipamorelin was given intravenously to improve gastric motility. The FDA states it has not identified safety information for certain other injectable routes and therefore lacks sufficient information to know whether the drug would cause harm by those routes 4. It is also sold as a 'research chemical'.

Doping status: Prohibited at all times (WADA S2, growth hormone secretagogues)

Checked against the WADA 2026 Prohibited List. For a specific product and country, Global DRO is the lookup athletes are expected to use — the List names substances, not brand names.

Mechanism of action

Ipamorelin is a synthetic pentapeptide that activates the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor targeted by the gastric hormone ghrelin. Activation on the somatotroph cells of the anterior pituitary leads, via the phospholipase C/IP3 pathway, to calcium influx and release of a GH pulse. It probably also suppresses somatostatin tone in the hypothalamus, so that the body's own GH pulsatility is amplified rather than replaced.

The distinguishing feature of ipamorelin is its selectivity. In the original characterisation (Raun et al., 1998) ipamorelin produced GH release comparable to GHRP-6, but caused no significant rise in ACTH or cortisol above the level also elicited by GHRH, and no change in prolactin, LH, FSH or TSH 1. The pronounced hunger effect of GHRP-6 is also largely absent. This makes ipamorelin pharmacologically the 'cleanest' of the GHRP class.

Because ipamorelin acts through the ghrelin receptor and GHRH analogues (sermorelin, mod GRF 1-29, CJC-1295, tesamorelin) act through a separate receptor (GHRH-R), the two classes work synergistically: combined administration produces a GH peak in human studies that is larger than the sum of the two separately. That is the pharmacological reason behind the common combination protocols. Negative feedback via IGF-1 and somatostatin remains intact, so a physiological ceiling exists that is absent with exogenous growth hormone.

What remains unknown: there are no long-term human studies of body composition, muscle strength or safety. Clinical development stopped before such data were collected.

What the research shows

That ipamorelin produces a dose-dependent GH peak in humans is well documented in phase 1 research. That it leads to more muscle mass, less fat mass or better recovery in healthy adults has not been shown. Selectivity with respect to cortisol and prolactin is the best-supported distinguishing feature.

Research in humans

Phase 1 research in healthy male volunteers characterised the pharmacokinetics and the dose-dependent GH response (Gobburu et al., Pharm Res 1999) 2. Novo Nordisk ran phase 2 research in postoperative ileus; that programme was discontinued because the primary endpoint was not met. There are no published randomised studies of body composition, muscle strength, sleep or recovery in healthy adults.

Animal and lab research

In rats and pigs ipamorelin produces robust, dose-dependent GH release. In hypophysectomised and young rats, chronic administration led to increases in body weight and bone growth. Animal models are, however, poor predictors of what prolonged submaximal GH stimulation does in adult humans.

Caveats. Almost all human data come from single-dose studies with small numbers of participants and surrogate endpoints (GH and IGF-1 levels), not from clinical outcomes. There is no replication of long-term use, no safety data over months to years, and no research in women or older adults. Virtually all dosing protocols circulating online come from user communities, not from published research.

What it is used for

  • Stimulating the body's own growth hormone release as an alternative to exogenous GH
  • Often combined with a GHRH analogue (mod GRF 1-29, CJC-1295, sermorelin) because of the synergistic effect
  • Used by users for recovery, sleep quality and body composition — none of these applications has been clinically confirmed
  • In research settings: postoperative ileus and gastrointestinal motility (unsuccessful)

Dosing

Dose
100-300 mcg per administration; user protocols typically cite 200-300 mcg, 1-3x per day
Frequency
1-3x daily, with at least 3 hours between administrations to limit receptor desensitisation
Route
subcutaneous, into subcutaneous fat (abdomen)
Duration
Cycles of 8-12 weeks with breaks are described in user protocols; no research establishes an optimal duration
  • These doses come from published user protocols and compounding practice, not from validated clinical studies. There is no approved dose. The only published human dose-ranging data are the five intravenous infusion levels of the phase 1 study (4.21 to 140.45 nmol/kg over 15 minutes), which do not translate directly into a subcutaneous microgram figure 2.
  • Administration on an empty stomach (at least 2 hours after eating, 30-60 minutes before eating) is advised because raised insulin and free fatty acids blunt the GH response.
  • Administration before sleep aligns with the natural nocturnal GH peak.
  • Above approximately 300 mcg the GH response does not increase proportionally (receptor saturation) and the risk of losing selectivity rises.
  • With prolonged continuous use without a break, desensitisation of the GHS-R1a receptor is plausible, although this has not been systematically quantified in humans.

These figures describe what the literature and published protocols report. They are not advice and not a dosing instruction.

Protocols

Ipamorelin, common user schedule

user protocol — not validated

Source: Pattern reported on forums and by vendors

This is not a validated schedule. It is a pattern that circulates among users and sellers, reproduced because it is what people actually follow — not because it has been tested. No trial established these doses, this interval or this duration, and nobody is checking what is in the vial. Treat every number below as an assertion, not a finding.

Before bed, at least 2 hours after eating200-300 mcg subcutaneously
Optional further dosesa morning and a post-training dose of 200-300 mcg, at least 3 hours apart, giving 1-3 doses per day
Weekly patternfive days on, two days off - usually weekdays with the weekend off
Run length8-12 weeks, then a break of roughly the same length

Above roughly 300 mcg per dose the GH response stops rising proportionally. Ipamorelin's selling point - GH release without a cortisol or prolactin rise - was demonstrated at low doses, and there is no basis for assuming the selectivity survives at higher ones. It is very often drawn into the same syringe as mod GRF 1-29 or CJC-1295, which means a reaction cannot be attributed to either compound.

Schedules are reproduced as their source states them. Units, IU and milligrams explains why the figures are not interchangeable between products.

Reconstitution

Vial sizes
2 mg, 5 mg, 10 mg
Solvent
bacteriostatic water (0.9% benzyl alcohol); sterile water only if used within 24 hours
Storage
Reconstituted 2-8 °C, stable for approximately 3-4 weeks. Lyophilised powder in the freezer (-20 °C), protected from light.

Worked example

5 mg vial + 2.5 ml bacteriostatic water = 2 mg/ml. 200 mcg = 0.1 ml = 10 units on a U100 insulin syringe.

Let the water run slowly down the wall of the vial rather than squirting it directly onto the powder. Do not shake — swirl gently. Do not freeze after reconstitution.

Work it out for Ipamorelin

Safety

Side effects

  • Redness, itching or brief swelling at the injection site
  • Brief headache, flushing or slight light-headedness shortly after injection (histamine-related)
  • Fluid retention and oedema, especially in the hands and ankles — a class effect of raised GH
  • Tingling or numbness in the hands; if persistent this may indicate carpal tunnel syndrome
  • Joint and muscle pain (arthralgia, myalgia)
  • Reduced insulin sensitivity and raised fasting glucose with more prolonged use
  • Fatigue or drowsiness after administration
  • Increased appetite has been described but is clearly less pronounced than with GHRP-6 or MK-677
  • Serious adverse events including death were identified in a published study of intravenous ipamorelin for gastric motility, and the FDA cites this among the significant safety risks that put ipamorelin acetate in category 2 of its compounding bulk substances policy 4
  • Immunogenicity: the FDA notes that compounded ipamorelin acetate may pose a risk of immune reaction for certain routes of administration, because of the potential for aggregation and peptide-related impurities 4

Do not use if

  • Active or treated malignancy, and a history of cancer — GH and IGF-1 are growth factors and there is a theoretical concern that they may stimulate existing malignant cells; with secretagogues this has been neither excluded nor refuted
  • Diabetes mellitus or impaired glucose tolerance without medical supervision
  • Active diabetic retinopathy
  • Pregnancy and breastfeeding — no safety data
  • Children and adolescents with open growth plates, outside medical supervision
  • Severe acute illness, following open heart surgery or in acute respiratory failure (by analogy with the warning for growth hormone)
  • Untreated pituitary or adrenal disorders

Interactions

Glucocorticoids suppress the GH response. Raised GH and IGF-1 lower insulin sensitivity, which may increase the need for insulin or oral antidiabetics. Growth hormone accelerates the conversion of cortisol to cortisone (11-beta-HSD-1 inhibition), which in people with adrenal insufficiency may increase hydrocortisone requirements, and it may affect the conversion of T4 to T3. Thyroid hormone and oestrogens (especially oral) affect the IGF-1 response. Other interactions have not been systematically studied.

Common questions

What is ipamorelin?
A selective GHRP — a ghrelin-receptor agonist — that triggers a short pulse of growth hormone without the rise in cortisol and prolactin seen with older GHRPs.
What is ipamorelin usually stacked with?
Most often with a GHRH analogue such as CJC-1295, because the two pull different levers of GH release. None of these combinations is an approved regimen.
Is ipamorelin better than MK-677?
They are different tools — ipamorelin is an injected pulse, MK-677 an oral round-the-clock rise. See MK-677 vs ipamorelin.

Sources