Ipamorelin vs. CJC-1295: GHRP and GHRH Analogs Compared

Ipamorelin and CJC-1295 both increase growth-hormone (GH) secretion, and they do it through two different doors. Ipamorelin is a growth-hormone-releasing peptide (GHRP): a small synthetic pentapeptide that activates the ghrelin receptor, GHS-R1a. CJC-1295 is a growth-hormone-releasing-hormone (GHRH) analog: a modified 29-residue fragment of the natural hypothalamic hormone that activates the GHRH receptor. Because the two receptors drive GH release through different intracellular pathways, activating both produces more GH than either alone — a synergy first shown in humans in 1990 and the reason the pair is the most common combination in growth-axis research. Profiles: Ipamorelin · CJC-1295.

Two receptors, one axis

Pituitary somatotrophs release GH in pulses set by the balance of two hypothalamic signals: GHRH, which stimulates, and somatostatin, which inhibits. GHRH acts through a G_s-coupled receptor and cyclic AMP; it both triggers release and drives synthesis of new GH. The ghrelin receptor uses a different transduction — G_q, phospholipase C and intracellular calcium — and, in addition to its direct effect on the somatotroph, acts in the hypothalamus to release GHRH and blunt somatostatin. Stimulating both receptors at once therefore does more than add two effects: it removes the brake while pressing both accelerators, which is the mechanistic basis of the supra-additive GH response.

Ipamorelin

Ipamorelin (Aib-His-D-2-Nal-D-Phe-Lys-NH₂) was developed at Novo Nordisk and described in 1998 as “the first selective growth hormone secretagogue”: in rats and pigs it released GH with a potency comparable to GHRP-6 but, unlike earlier GHRPs, did not release ACTH or cortisol at GH-releasing doses, and had little effect on prolactin. That selectivity is its defining feature. It is short-acting — a plasma half-life of roughly two hours in humans — and has been through Phase 2 trials, not for growth-hormone indications but for post-operative ileus, on the strength of the ghrelin receptor’s role in gut motility. In animal work it counteracts glucocorticoid-induced bone loss and stimulates longitudinal bone growth.

CJC-1295: DAC and no-DAC are different molecules

The name CJC-1295 is used for two related compounds, and the difference matters more than any other detail in this comparison.

• CJC-1295 with DAC is the molecule ConjuChem developed and put into clinical trials: a tetra-substituted GRF(1–29) fitted with a “Drug Affinity Complex” — a reactive linker that covalently binds the peptide to serum albumin after administration. That conjugation gives it a half-life of roughly six to eight days, and a single dose in healthy adults raised GH and IGF-1 for a week or more, with GH pulsatility preserved. Its only registered trial was terminated, and it was never approved.
• CJC-1295 without DAC — the form supplied as CJC-1295 5 mg (no DAC) and often called modified GRF(1–29) — is the same tetra-substituted peptide (D-Ala², Gln⁸, Ala¹⁵, Leu²⁷) without the albumin-binding linker. The substitutions protect it from DPP-4 and other proteases better than the native fragment (sermorelin), but with no DAC its half-life is measured in minutes rather than days, and it produces a discrete GH pulse rather than a sustained elevation.

The validated precedent for the GHRH-analog class is tesamorelin, an approved 44-residue GRF analog — the compound to read when you want to know what a GHRH analog does in humans over months.

Side by side

The synergy literature

Bowers and colleagues showed in 1990 that a GHRP given together with GHRH to normal men produced a GH response greater than the sum of the two alone. Later work from the same group dissected what determines the synergy — the timing of the two signals relative to endogenous pulses, sex-steroid milieu, and age — and the picture that emerged is consistent with the two-receptor mechanism above. Two things about that literature should be kept in view. The synergy experiments used GHRP-2 or GHRP-6 with native GHRH, not ipamorelin with modified GRF(1–29); the extrapolation to the current pair is mechanistically reasonable but not directly tested. And the effect is on GH secretion; downstream outcomes in any tissue are a separate question that the acute-secretion studies do not answer.

Research applications

• Growth-axis pharmacology — dissecting GHRH-R versus GHS-R1a contributions, pulsatility and feedback.
• Catabolic and glucocorticoid models (ipamorelin’s bone and nitrogen-balance studies).
• Gastrointestinal motility (the ghrelin-receptor side).
• Anti-doping analytical chemistry — GHRH analogs and GHRPs are prohibited in sport, and both compounds appear in the detection literature.

Both are supplied lyophilized: Ipamorelin 10 mg and CJC-1295 5 mg (no DAC). Handling is standard (see How to reconstitute); note that GRF(1–29) analogs contain no methionine — one of the reasons the Leu²⁷ substitution was made — which removes the oxidation liability of the native sequence.