Ipamorelin

Ipamorelin is a synthetic pentapeptide that activates the growth hormone secretagogue receptor 1a (GHSR1a, the ghrelin receptor) in the pituitary and hypothalamus. It is the most selective GHRP (growth hormone releasing peptide) characterized to date, producing GH release without meaningfully affecting cortisol, ACTH, prolactin, or appetite. Ipamorelin was first described in 1998 by Karen Raun and the Novo Nordisk research group as part of the GHRP-1, GHRP-2, GHRP-6, and hexarelin family.

The molecule has a five-amino-acid sequence (Aib-His-D-2-Nal-D-Phe-Lys-NH₂) with a molecular weight of 711 Da. The pentapeptide is short enough to be synthesized at high purity and stable enough to survive subcutaneous administration. The plasma half-life is approximately 1.5 to 2.5 hours, with peak GH effect at around 40 minutes after injection. The GH-releasing effect lasts roughly 3 hours per dose, which is why typical dosing protocols use multiple injections per day.

Ipamorelin was originally developed for postoperative ileus (gut paralysis after surgery). Helsinn Therapeutics took the compound through Phase 2 trials in that indication in the 2000s, with results published in 2007 to 2010. The trials confirmed safety and tolerability but did not show clinically meaningful improvement in the primary endpoints. Commercial development for the GI indication ceased. The molecule has been used off-label in adult GH optimization settings since.

The Published Human Evidence

Two trial programs make up the published human data on ipamorelin.

Original characterization studies (1998 to 2003). Karen Raun and colleagues at Novo Nordisk published several Phase 1 studies in healthy male subjects establishing the GH-releasing profile, selectivity for GH over cortisol/ACTH/prolactin, and dose-response relationship. The studies included around 60 to 100 healthy subjects across multiple papers.

Postoperative ileus trials (mid-2000s). Helsinn Therapeutics tested ipamorelin in patients recovering from gastrointestinal surgery as a treatment for postoperative ileus. Phase 2 trials were generally well-tolerated but did not show clinically meaningful improvement in primary endpoints such as time to first bowel movement or hospital length of stay. Commercial development ceased.

Beyond these, there is limited additional human data. No Phase 3 trial of ipamorelin has been completed in any indication. The compound has been used in compounded clinical settings for over two decades, but the published evidence base has not grown substantially during that period.

A 2019 GH stimulation study referenced in compounding literature reported consistent GH increase 30 to 60 minutes after injection at 200 mcg daily over 8 weeks. The replicability of the GH response is one of the most consistent findings across the ipamorelin literature.

Ipamorelin acts on the ghrelin receptor (GHSR1a) rather than the GHRH receptor. This is the key mechanistic distinction from GHRH analogs like sermorelin, CJC-1295, and tesamorelin.

GHSR1a is the receptor for ghrelin, the gut-secreted hormone that drives hunger and also stimulates GH release. The receptor is expressed on pituitary somatotrophs alongside the GHRH receptor. Activation triggers a GH pulse through a partially overlapping but distinct intracellular cascade compared with GHRH receptor activation. The pituitary releases GH from secretory granules, with the magnitude depending on stored GH content and the recovery time since the last pulse.

The selectivity profile is what makes ipamorelin unusual in the GHRP class. Older ghrelin receptor agonists (GHRP-6, GHRP-2, hexarelin) all produced GH release plus measurable elevations in cortisol, ACTH, and prolactin. Ipamorelin's structural design appears to bias the receptor toward GH release while minimizing the off-target endocrine effects. The 1998 Raun paper documented GH increase with no statistically significant change in cortisol, ACTH, prolactin, or aldosterone at therapeutic doses.

The other practical effect of this selectivity is reduced appetite stimulation. Ghrelin is the hunger hormone, and ghrelin receptor agonists are expected to increase appetite as a class effect. Ipamorelin produces this effect to a lesser degree than GHRP-2 or GHRP-6, though it does not eliminate it entirely. Users typically report some increase in appetite, particularly during the first weeks of dosing.

GH Pulse Characteristics

The most consistently documented effect of ipamorelin is the acute GH pulse after subcutaneous administration. The 1998 Raun characterization showed peak GH approximately 40 minutes after injection, returning to baseline within 3 hours. Peak GH levels in the original Phase 1 work reached approximately 20 to 40 ng/mL in healthy young men at therapeutic doses, compared with baseline values typically below 1 ng/mL in fasted resting subjects. The magnitude of the GH pulse from ipamorelin alone is roughly comparable to a strong physiological GH pulse during slow-wave sleep.

The GH increase is dose-dependent over a defined range. Doses below 50 mcg in adults produce minimal GH response. Doses between 100 and 300 mcg produce the substantial GH pulses described above. Doses above 500 mcg do not produce proportionally larger GH responses, because the pituitary GH output is rate-limited by stored GH availability rather than by ghrelin receptor activation alone.

Selectivity for GH Over Other Pituitary Hormones

The hallmark feature of ipamorelin compared with older GHRPs is the clean selectivity profile. Raun et al. and subsequent characterization work consistently showed no statistically significant change in:

Cortisol. Older GHRPs (GHRP-2, GHRP-6, hexarelin) increase cortisol by approximately 15 to 30 percent. Ipamorelin produces no measurable change at therapeutic doses.

ACTH. Same pattern as cortisol. No measurable increase with ipamorelin.

Prolactin. Older GHRPs raise prolactin by approximately 30 to 60 percent. Ipamorelin produces no significant change.

Aldosterone. No measurable effect.

Insulin. Mild transient increase, comparable to the indirect effect from GH itself rather than direct ghrelin receptor signaling.

This selectivity is the central reason ipamorelin became the dominant GHRP in adult off-label compounding settings after the older GHRPs fell out of favor. The clean profile reduces the off-target effects (water retention, mood changes, prolactin-related symptoms) that limit GHRP-2 and GHRP-6 use.

IGF-1 Response

Sustained daily or twice-daily ipamorelin produces measurable IGF-1 increase of approximately 20 to 50 percent above baseline within 2 to 4 weeks. The response depends on baseline IGF-1, age, and concurrent use of GHRH analogs. Ipamorelin alone produces a smaller IGF-1 response than stacked protocols that combine ipamorelin with CJC-1295 or sermorelin, because the combination produces a larger integrated 24-hour GH exposure than either compound alone.

Subjective Effects in Off-Label Adult Use

Adult off-label users report a consistent pattern of subjective effects, though none has Phase 3 trial-grade evidence backing.

Improved sleep quality. Reported most consistently, often within the first week of use. The mechanistic plausibility is strong because GH release is closely linked with slow-wave sleep architecture.

Recovery from training. Reports of reduced soreness, improved recovery between sessions, and improved exercise tolerance. The effect is difficult to separate from training-effect confounding in uncontrolled use.

Body composition. Modest reductions in body fat and increases in lean mass over 3 to 6 months of consistent use. The magnitude is smaller than what rhGH replacement produces and is highly dependent on concurrent nutrition and resistance training.

Mild appetite increase. Present in most users, more prominent during the first weeks. Generally less marked than with GHRP-2 or GHRP-6.

Skin and connective tissue. Subjective reports of improved skin elasticity and hair quality. Observational rather than controlled.

None of the subjective off-label effects has the trial-grade evidence backing of the GH pulse and IGF-1 response.

This compound is on the World Anti-Doping Agency (WADA) Prohibited List. Use in competitive sport, in-competition or out-of-competition, constitutes an anti-doping rule violation.

Phase 1 Trial Doses

The original Raun 1998 characterization tested single subcutaneous doses of approximately 0.5 mcg/kg, 2 mcg/kg, and 6 mcg/kg in healthy male subjects. The 2 mcg/kg dose corresponds to approximately 150 mcg in a 75 kg adult. Higher doses up to 80 mcg/kg were tested in dose-escalation work without serious adverse events. The peak GH response was dose-dependent at the lower doses and approached a plateau at the higher doses, consistent with the rate-limited pituitary GH output described above.

The Helsinn postoperative ileus program tested doses of 0.03 mg/kg twice daily intravenously in surgical patients, which corresponds to approximately 2 mg twice daily in a 75 kg adult. These doses were used for short-term hospital administration and are substantially higher than adult off-label compounded protocols.

Adult Off-Label Compounded Protocols

The compounding-pharmacy protocols established in clinical practice from the 2010s onward use the following ranges.

Standalone ipamorelin: 200 to 300 mcg administered subcutaneously once daily before bed, or split into two or three smaller injections of 100 mcg each given before meals and at bedtime. The pre-bed timing aligns the GH pulse with the natural nocturnal pulse during slow-wave sleep.

Stack with CJC-1295 (no DAC): 100 to 300 mcg of ipamorelin combined with 100 to 300 mcg of CJC-1295 no DAC (modified GRF 1-29) in the same injection, administered subcutaneously once daily before bed. This is the dominant adult off-label GH peptide protocol. The pre-bed timing applies for the same reason as standalone ipamorelin. The dual-receptor activation produces a larger GH pulse than either compound alone.

Stack with CJC-1295 with DAC: Less common. 100 to 300 mcg of ipamorelin daily plus 1 to 2 mg of CJC-1295 with DAC once or twice weekly. The asymmetric dosing reflects the dramatically different half-lives. CJC-1295 with DAC sustains weekly GHRH receptor activation while ipamorelin produces daily pulses on top.

Stack with sermorelin: 100 to 300 mcg of ipamorelin daily plus 200 to 500 mcg of sermorelin daily, both administered subcutaneously in the same evening injection. Sermorelin contributes the GHRH receptor signal. Ipamorelin contributes the ghrelin receptor signal.

Pharmacokinetics

Ipamorelin has a plasma half-life of approximately 1.5 to 2.5 hours after subcutaneous injection. Peak GH response occurs at 40 minutes. The GH pulse returns to baseline within 3 hours of injection. The peptide is cleared by proteolytic degradation in plasma and tissue.

Multiple daily injections do not produce GH pulses of identical magnitude. The second dose of the day typically produces a smaller GH response than the first because pituitary stored GH has not fully recovered between pulses. This is the pharmacological basis for the 4-to-6-hour spacing in multi-injection daily protocols.

Cycling Patterns

Adult off-label protocols typically use cycling patterns of 8 to 12 weeks continuous use followed by 4 to 6 weeks off. The rationale is to limit potential ghrelin receptor desensitization from sustained daily stimulation. No published human pharmacokinetic data documents that cycling produces better IGF-1 outcomes than continuous use, and the rationale is mechanistic rather than evidence-based. Some protocols use shorter on-off ratios (such as 5-on, 2-off weekly cycling) instead.

Why Stack Ratios Vary

Adult off-label CJC-1295/ipamorelin combinations vary the dose ratio between the two compounds based on the desired emphasis. Higher ipamorelin relative to CJC-1295 emphasizes the pulsatile, ghrelin-driven response. Higher CJC-1295 relative to ipamorelin emphasizes the sustained GHRH receptor signal. The standard 1:1 ratio at 100 to 300 mcg of each is the most commonly prescribed in compounding practice, but no controlled trial has identified an optimal ratio. The honest summary is that the 1:1 ratio became the default in clinical compounding for convenience and dose-matching, not because of trial evidence.

The published Phase 1 and Phase 2 data describes a generally clean safety profile. The most commonly reported adverse events at therapeutic doses are:

Mild injection-site reactions (redness, swelling, transient discomfort) in approximately 5 to 10 percent of subjects. Most resolve spontaneously within hours.

Headache in approximately 5 to 15 percent of subjects, typically mild and transient.

Flushing and warmth during the first 30 minutes after injection. This is the GH pulse effect and tends to diminish with continued dosing.

Mild appetite stimulation. The ghrelin receptor effect is more muted than with GHRP-2 or GHRP-6 but is present. Some users report measurable weight gain if food intake is not actively controlled.

Lethargy or sedation. Some users report a mild "drugged" sensation, particularly at higher doses. The mechanism appears related to ghrelin's broader effects on hypothalamic signaling.

The Helsinn postoperative ileus trials did not flag serious adverse events. The compound was generally well-tolerated in hospitalized patients receiving daily doses for up to 7 days. Long-term safety data in healthy adults at compounded doses is limited.

Theoretical class concerns include the same IGF-1-related cancer risk that applies to all GH secretagogues, transient glucose increase due to GH-induced insulin resistance, and fluid retention at higher doses. None of these has been documented as a clinically significant issue in the published ipamorelin literature.

Ipamorelin sits in a specific position in the GH secretagogue class.

Ipamorelin vs GHRP-2. GHRP-2 is more potent at raw GH stimulation. Combined GHRH + GHRP-2 has produced up to 54-fold GH increases in some trials, versus around 20-fold with GHRH alone. The cost is meaningfully higher cortisol, prolactin, and appetite increase. Ipamorelin trades some potency for selectivity.

Ipamorelin vs GHRP-6. GHRP-6 was the original commercially available GHRP. It produces strong appetite stimulation and measurable cortisol/prolactin increase. Ipamorelin is the cleaner choice for adult body-composition applications where appetite increase is undesirable.

Ipamorelin vs MK-677. MK-677 is also a ghrelin receptor agonist, but it is an orally bioavailable small molecule rather than a peptide. MK-677 produces sustained 24-hour GH/IGF-1 increase from once-daily oral dosing. Ipamorelin produces a discrete 3-hour pulse from subcutaneous injection. MK-677 has the larger Phase 2 evidence base (1,200+ subjects across published trials). Both are on the FDA Category 2 list.

For most adult off-label GH optimization, ipamorelin is the dominant GHRP in compounding settings due to the selectivity advantage. Whether that position survives the PCAC vote in July 2026 is an open question.

For informational and educational purposes only. Not medical advice. Not for human consumption unless prescribed by a licensed physician for an FDA-approved indication. Consult a qualified healthcare provider before using any peptide or pharmaceutical product.