Ipamorelin

Ipamorelin (NNC 26-0161) is a selective pentapeptide growth hormone secretagogue acting as an agonist at the growth hormone secretagogue receptor (GHS-R1a), the ghrelin receptor. It stimulates endogenous somatotroph output rather than introducing exogenous GH.

Its action is threefold: direct GHS-R1a agonism at pituitary somatotrophs, stimulated release of somatocrinin (GHRH) from the hypothalamus, and inhibition of somatostatin, the GH-inhibiting hormone that also regulates broader endocrine and neurotransmission activity. The net effect is pulsatile GH release that follows physiological rhythm rather than a flat exogenous level.

Selectivity is the distinguishing feature. Raun et al. (1998) found GH-releasing potency and efficacy similar to GHRP-6 but no significant increase in ACTH or cortisol at doses more than 200 times the effective dose for GH release, and no effect on FSH, LH, prolactin, or TSH. Minimal impact on acetylcholine, prolactin, cortisol, and aldosterone is the basis for its long-term-use profile and why it is generally preferred over GHRP-2 and GHRP-6 where sustained dosing is intended.

Developed by Novo Nordisk in Denmark, it advanced to Phase 2 for post-operative ileus and was discontinued after failing to meet efficacy endpoints (Beck et al., 2014). It holds no FDA approval for human use.

GH secretion is governed by two arms: hypothalamic GHRH, which drives synthesis and release at pituitary somatotrophs, and ghrelin, which triggers release of stored GH via GHS-R1a while simultaneously suppressing somatostatin, the inhibitory brake. Ipamorelin mimics the ghrelin arm, binding GHS-R1a in the pituitary to produce a rapid GH pulse rather than the sustained elevation seen with exogenous GH.

Pharmacokinetics in humans (Gobburu et al., 1999): half-life approximately 2 hours, GH peaking at 0.67 hours (about 40 minutes) post-injection, dose-dependent response across all tested doses, with GH declining exponentially back to baseline.

The pulsatile profile preserves physiological architecture — the largest endogenous pulse occurs in slow-wave sleep, with secondary pulses post-exercise and in fasted states — leaving negative feedback intact. Johansen et al. (1999) found pituitary GH content unchanged, indicating no depletion or suppression of the somatotroph reserve.

Downstream, released GH drives hepatic IGF-1 production, and IGF-1 mediates muscle protein synthesis, lipid metabolism, cellular repair, collagen synthesis, and tissue growth. The full GH/IGF-1 axis must be functional for outcomes to follow.

Co-activation of both arms is markedly supra-additive. Pairing a GHRH analogue such as CJC-1295 No DAC with a ghrelin agonist produces a GH pulse reported at 77 to 225% greater than either compound alone: the GHRH analogue raises production capacity while Ipamorelin triggers release and removes somatostatin inhibition.

Somatotropic axis: GHS-R1a agonism produces pulsatile GH release mimicking endogenous secretion, with downstream IGF-1-mediated anabolic effect — increased collagen synthesis, muscle regeneration, lean mass accrual, and protection against sarcopenic and drug-induced muscle wasting. Lu et al. (2024) reported inhibition of cisplatin-induced weight loss by approximately 24% in the delayed phase (48 to 72 hours) in ferrets. Selectivity for GH over ACTH, cortisol, prolactin, acetylcholine, and aldosterone underpins the long-term-use profile.

Skeletal: increased bone density and bone mineral content with support for bone formation, growth, and longitudinal development. Andersen et al. (2001) showed reversal of glucocorticoid-induced suppression of bone formation with periosteal bone formation rate increased up to four-fold versus glucocorticoid alone, plus significantly increased maximum tetanic tension in muscle, in 8-month-old female rats treated for 3 months. Johansen et al. (1999) showed dose-dependent longitudinal bone growth from 42 to 52 microns per day with unchanged pituitary GH content. Svensson et al. (2000) examined bone mineral content in adult female rats.

Metabolic and GI: enhanced metabolic rate and lipolysis via GH-mediated hormone-sensitive lipase activation, with reduced adiposity reported particularly at the midsection; improved glycaemic regulation; improved gut health with gastroprotection against ulceration; improved gastric tissue health; accelerated gastric emptying and GI transit — the last a direct consequence of ghrelin receptor agonism rather than of GH, and the rationale for the post-operative ileus programme.

Regenerative: chondrogenesis-mediated cartilage repair, improved collagen synthesis, accelerated healing of injured tissue, with connective tissue and dermal effects emerging on a longer timescale than recovery or sleep effects.

Sleep: increased slow-wave sleep, clinically relevant since the largest endogenous GH pulse occurs in deep sleep.

Immune: increased leukocyte, T-cell, and B-cell counts, reduced inflammation, improved phagocyte activity, correction of disease-driven catabolic metabolic states.

CNS: improved cognitive function and neuroprotection, prevention of age-related dopaminergic loss implicated in Alzheimer's and Parkinson's disease, improved memory and problem solving.

Appetite: orexigenic effect present but markedly attenuated relative to GHRP-6 and MK-677, a direct consequence of its selectivity.

Other systemic: improved cardiovascular function, increased libido and improvement in erectile dysfunction, increased oestrogen and sexual desire in women.

Weeks 1 to 2: sleep quality is the earliest and most consistently reported change — shorter sleep latency, deeper sleep, improved waking state — consistent with amplification of the slow-wave-sleep GH pulse. Mild injection site reactions and transient flushing or head rush immediately post-injection are common and usually settle with adaptation.

Weeks 2 to 4: recovery markers improve — reduced inter-session soreness and lower daytime fatigue. A modest orexigenic effect may appear, markedly milder than GHRP-6 or MK-677.

Weeks 4 to 8: body composition begins to shift, with fat loss becoming apparent where nutrition and training are consistent; improved muscle fullness and early skin quality changes are reported.

Weeks 8 to 12 and beyond: the larger body composition, connective tissue, and joint comfort effects emerge as IGF-1-driven collagen synthesis accumulates — skin quality, joint comfort, tendon health. Aggregated user reports place full body composition change at 3 to 6 months, with visible midsection leanness commonly cited at 8 to 12 weeks, and hair and nail growth occasionally reported as early markers of raised GH activity.

Across 16 to 24 weeks of consistent use, sleep quality and more efficient fat loss are the two dominant reported outcomes; hypertrophy and strength responses are reported as minimal by some users, including those already on testosterone replacement. GH optimisation is a long-horizon intervention that amplifies existing training, nutrition, and sleep rather than substituting for them. Baseline IGF-1 with a retest at 8 to 12 weeks is the objective check on whether the protocol is working.

Studied doses: Gobburu et al. (1999) tested multiple escalating intravenous doses in 40 healthy male volunteers. Beck et al. (2014) used 0.03 mg/kg (approximately 2 to 3 mg) intravenously twice daily. No published dose-finding study exists for the subcutaneous protocols used in practice; the protocols below reflect clinical practice patterns and usual practice rather than trial-derived dosing.

Reconstitution: 5 mg vial with 2 mL bacteriostatic water, yielding 250 mcg per 10 units on an insulin syringe. Diluent down the vial wall, swirl, do not shake. Blend vial (5 mg CJC-1295 No DAC + 5 mg Ipamorelin): 2 mL bacteriostatic water, 4 units for 100 mcg of each compound per dose. An alternative practice pattern reconstitutes a 10 mg vial with 2.5 mL (4 mg/mL) and opens at 100 mcg once daily, held until fully tolerated before escalating.

Administration: subcutaneous, injected slowly — flushing and paraesthesia are rate-dependent rather than dose-dependent.

Fasted dosing is not optional if GH output is the goal: postprandial insulin, driven particularly by carbohydrate, blunts the somatotroph response. At least 2 hours post-prandial before injection and 30 minutes post-injection before eating.

Timing follows endogenous pulse structure. Pre-bed captures the slow-wave-sleep pulse. Twice daily adds an on-waking fasted dose. Some practice patterns add a third administration within 30 minutes post-workout to exploit the exercise-induced pulse.

Split dosing for maximum pulsatility: 100 to 150 mcg Ipamorelin plus 100 to 150 mcg CJC-1295 morning fasted, and 100 to 150 mcg of each before bed, generating two discrete GH pulses per day.

Body-weight tiering: under 150 lbs, 100 to 150 mcg per injection; 150 to 200 lbs, 150 to 200 mcg per injection; over 200 lbs, 200 to 300 mcg per injection. Note that the 200 to 300 mcg solo doses recommended by some clinics sit above what most users report running successfully.

Cycling: daily dosing, 12 to 16 weeks on, 4 weeks off. The 5-on, 2-off schedule has no scientific basis — acute GHS-R1a desensitisation clears in roughly 60 minutes after each dose, while chronic desensitisation takes approximately 16 weeks of continuous use to develop and 4 weeks off to fully reverse, per the hexarelin desensitisation literature (Rahim and Shalet, 1998). Two rest days per week accomplish nothing.

Dose-reduce rather than discontinue on mood change or irritability, reported by a small number of users above 200 mcg and particularly in tesamorelin blends. Persistent hand numbness or tingling, facial or joint swelling, or carpal tunnel symptoms indicate the dose is too high.

Evidence base: one landmark preclinical selectivity study, one human pharmacokinetic study, several rodent bone studies, one failed Phase 2 trial, and one recent animal cachexia model. No long-term human data.

Raun et al., 1998 (European Journal of Endocrinology), in swine and rat models, established Ipamorelin as the first selective GHS-R1a agonist. GH release matched GHRP-6 in potency and efficacy, yet ACTH and cortisol were unchanged at doses more than 200 times the effective GH-releasing dose, with no effect on FSH, LH, prolactin, or TSH. This is the basis for the selectivity claim and for preference over GHRP-2 and GHRP-6 in sustained dosing.

Gobburu et al., 1999 (Pharmaceutical Research), a dose-escalation study in 40 healthy male volunteers, remains the only published human pharmacokinetic dataset. Half-life approximately 2 hours; GH Cmax at 0.67 hours (about 40 minutes) post-injection; dose-dependent response across all doses tested; exponential decline to baseline; well tolerated throughout. It characterised pharmacology, not clinical outcomes.

Skeletal work is rodent. Andersen et al., 2001 (Growth Hormone and IGF Research) treated 8-month-old female rats with glucocorticoids for 3 months: Ipamorelin counteracted the glucocorticoid-induced fall in bone formation, raised periosteal bone formation rate up to four-fold versus glucocorticoid alone, and significantly increased maximum tetanic tension. Johansen et al., 1999 showed dose-dependent longitudinal growth rate rising from 42 to 52 microns per day with pituitary GH content unchanged, arguing against somatotroph depletion. Svensson et al., 2000 reported increased bone mineral content in adult female rats for both Ipamorelin and GHRP-6.

Beck et al., 2014 (International Journal of Colorectal Disease) was a Phase 2 multicentre, double-blind, placebo-controlled randomised trial in 114 bowel resection patients using 0.03 mg/kg (approximately 2 to 3 mg) intravenously twice daily for up to 7 days. Well tolerated, but time to tolerate solid food was not significantly improved (25.3 versus 32.6 hours, p = 0.15) and Novo Nordisk discontinued development. Its value now is human safety signal, not efficacy.

Lu et al., 2024 (Physiology and Behavior) found Ipamorelin inhibited cisplatin-induced weight loss in ferrets by approximately 24% in the delayed phase (48 to 72 hours), supporting an anti-catabolic role. Ishida et al., 2020 provides the broader GHS class review. No published dose-finding study supports the subcutaneous protocols used in practice.