What Is GHRP-2?
GHRP-2 is a synthetic hexapeptide belonging to the growth hormone secretagogue (GHS) class of compounds. Its sequence, D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH2, incorporates unnatural D-amino acids that confer resistance to enzymatic degradation and improve receptor binding affinity compared to earlier peptides in the series.
The GHRP lineage began in 1984 when Bowers demonstrated that chemical analogs of met-enkephalin exhibited unexpected GH-releasing activity in pituitary cell cultures. GHRP-6 emerged as the first clinically studied member of the family, followed by GHRP-1, GHRP-2, and hexarelin. Among these, GHRP-2 was optimized for higher GH-releasing potency and a more favorable secondary hormone profile.
In Japan, GHRP-2 is marketed under the name pralmorelin (brand name GHRP Kaken) by Kaken Pharmaceutical. It received regulatory approval from the Pharmaceuticals and Medical Devices Agency (PMDA) in October 2004 as a diagnostic tool for assessing GH deficiency in adults and children over four years of age. Kaken sublicensed North American rights to Wyeth, but the compound never advanced to FDA approval.
GHRP-2 is distinct from the other major GHRPs in meaningful ways. Compared to GHRP-6, it produces higher peak GH levels with less pronounced hunger, cortisol elevation, and prolactin stimulation. Compared to ipamorelin, which is considered the most selective GHRP, GHRP-2 achieves greater absolute GH output but at the cost of moderate effects on the ACTH-cortisol axis and prolactin secretion that ipamorelin avoids entirely.
How It Works
GHS-R1a Receptor Agonism
GHRP-2 functions as an agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the same receptor that responds to the endogenous hormone ghrelin. GHS-R1a is a G-protein coupled receptor expressed primarily on somatotroph cells in the anterior pituitary gland and in the hypothalamic arcuate nucleus.
Upon binding, GHRP-2 activates Gq/11 signaling pathways, leading to phospholipase C activation and the generation of inositol trisphosphate (IP3) and diacylglycerol (DAG). This cascade mobilizes calcium from intracellular stores, triggering exocytosis of GH-containing secretory granules and producing acute GH release. Beyond GHS-R1a, GHRPs also interact with the CD36 scavenger receptor, which appears to mediate some of their documented cytoprotective and cardiovascular effects.
Unlike exogenous GH administration, GHRP-2 works within the body's endogenous feedback loops. Somatostatin-mediated negative feedback remains intact, which means GHRP-2 amplifies natural GH pulses rather than creating a constant supraphysiological elevation. This built-in regulatory mechanism makes it difficult to overshoot GH levels to a dangerous degree.
Growth Hormone Release Profile
GHRP-2 is among the most potent GH secretagogues by peak output. Clinical data show that a single subcutaneous injection produces peak plasma GH concentrations of 30 to 100 ng/mL within 15 to 30 minutes, representing 8- to 20-fold increases above baseline depending on dose and individual response.
In the pivotal comparative study by Arvat et al. (1997), GHRP-2 at 1 mcg/kg produced GH responses that exceeded those induced by the maximal effective dose of GHRH in healthy young adults, based on intravenous administration in a controlled clinical setting. The GH-releasing effect is dose-dependent up to approximately 2 mcg/kg, beyond which a plateau occurs. Co-administration with GHRH analogs produces synergistic effects, with combined GH responses two to three times greater than either agent alone.
In the Japanese diagnostic application, plasma GH levels after a single pralmorelin injection exceed 15 mcg/L in healthy subjects but remain below 15 mcg/L in patients with severe GH deficiency, forming the basis of its use as a provocative test.
Effects on Cortisol and Prolactin
GHRP-2 produces moderate stimulation of the ACTH-cortisol axis and prolactin secretion. Arvat et al. demonstrated that all tested doses of GHRP-2 stimulated ACTH and cortisol to a similar extent, with responses comparable to those produced by human corticotropin-releasing hormone (hCRH). Prolactin elevation was present but lower than that induced by thyrotropin-releasing hormone (TRH).
This profile positions GHRP-2 between GHRP-6 (which tends to produce stronger cortisol and prolactin spikes) and ipamorelin (which does not meaningfully affect either hormone even at doses exceeding 200 times its GH-releasing ED50). For users concerned about cortisol-related effects such as impaired recovery or sleep disruption, or prolactin-related effects such as reduced libido, the moderate profile of GHRP-2 is a relevant consideration when choosing among GHRPs.
Appetite Stimulation
As a ghrelin receptor agonist, GHRP-2 stimulates appetite. A controlled study by Laferrere et al. (2005) published in the Journal of Clinical Endocrinology & Metabolism confirmed that GHRP-2 increases food intake in healthy men through ghrelin-mediated pathways.
However, the appetite effect is moderate compared to GHRP-6, which triggers robust, acute hunger shortly after dosing. This distinction matters in practice: users pursuing body recomposition or fat loss often prefer GHRP-2 or ipamorelin over GHRP-6 specifically because the hunger response is more manageable and less likely to derail dietary adherence.