Pralmorelin

An Approved Diagnostic Drug, Not a Research Chemical

Pralmorelin is the international nonproprietary name for the compound the peptide community knows as GHRP-2, and in Japan it exists as something unusual for this drug class — a regulator-approved pharmaceutical product. This page focuses on pralmorelin as the approved intravenous diagnostic agent marketed by Kaken Pharmaceutical (brand name GHRP Kaken 100, with the longer-acting oral diagnostic formulation also developed in the Japanese program). For the research-chemical community framing, subcutaneous dosing protocols, and stacking logic, see our separate GHRP-2 page.

Structure and Pharmacology

Pralmorelin is a synthetic hexapeptide, D-Ala-D-β-Nal-Ala-Trp-D-Phe-Lys-NH₂, developed by Kaken Pharmaceutical in the early 1990s (development code KP-102) as a more potent successor to the first-generation GHRP-6. It is a full agonist at the ghrelin receptor (GHSR-1a) on pituitary somatotrophs, producing rapid pulsatile growth hormone release. Mechanistically it sits in the same class as ipamorelin and hexarelin, but with higher milligram potency than either and a somewhat less clean non-GH hormone profile — pralmorelin drives measurable cortisol and prolactin increases at GH-effective doses.

The Japanese Diagnostic Approval

Kaken pursued pralmorelin not as a treatment but as a GH deficiency diagnostic. The clinical problem it addressed is real: the historical gold-standard test for adult GH deficiency — the insulin tolerance test — is burdensome, requires close medical supervision for induced hypoglycemia, and is contraindicated in patients with seizure history or ischemic cardiac disease. A pharmacological GH secretagogue given intravenously offered a safer, faster alternative.

The Japanese development program ran through the late 1990s and early 2000s:

• Multicenter pharmacodynamic studies characterized the dose-response of IV pralmorelin in healthy adults and in patients with confirmed hypopituitarism.
• Sensitivity and specificity for adult GH deficiency, benchmarked against ITT, were reported in the ranges that supported diagnostic use — high 80s to low 90s percent for both.
• Tolerability in the diagnostic setting was favorable, with transient flushing and mild injection-site reactions the dominant adverse events.

Kaken received Japanese Ministry of Health, Labour and Welfare approval in 2006 for intravenous pralmorelin as a GH stimulation test for adult GH deficiency. That approval remains in force and pralmorelin is listed in Japanese diagnostic algorithms for pituitary dysfunction.

Why the Approval Stayed Regional

Pralmorelin was never approved by the FDA, EMA, or most other major regulators. Several factors contributed:

• Competing non-peptide agents. Western development interest shifted toward oral non-peptide ghrelin agonists — most notably macimorelin, which received FDA approval in December 2017 for adult GH deficiency diagnosis and offers the significant practical advantage of oral rather than intravenous administration.
• Limited commercial case. GH stimulation testing is a niche endocrinology application with modest global volume, and the commercial return on pursuing a second-line injectable diagnostic outside Japan was unattractive.
• Cortisol and prolactin signal. Pralmorelin's non-GH hormonal effects, while manageable in a single-dose diagnostic context, complicated any attempt to reposition the molecule for therapeutic GH deficiency indications.

Clinical Use in Practice

In Japanese endocrinology practice, the IV pralmorelin test is administered as a single 100 mcg dose with serial plasma GH sampling at 0, 15, 30, 45, and 60 minutes. Peak GH below a defined threshold (typically 9 ng/mL, with cutoffs varying by protocol) supports the diagnosis of adult GH deficiency. The test is fast, well-tolerated, and does not require the medical supervision intensity of insulin tolerance testing.

The Research-Chemical Gap

The critical distinction: the subcutaneous pralmorelin / GHRP-2 product sold by research-chemical vendors worldwide is not the regulated Kaken diagnostic product. It comes from a different supply chain, is not subject to pharmaceutical-grade quality controls, and is used for a different purpose (chronic body-composition dosing rather than single-dose diagnostic testing). The approved Japanese indication does not validate gray-market use of the molecule, and the pharmacology, cortisol concerns, and WADA status covered on the main GHRP-2 page apply fully to that research-chemical context.