GHRP-2 is a synthetic six-residue growth hormone secretagogue, also known as pralmorelin or KP-102. It activates ghrelin-receptor signaling and has two well-characterized acute effects in people: GH release and increased food intake during controlled meals. Its clinical development also includes diagnostic testing of the pituitary’s capacity to release GH. These uses make the physiological response easier to interpret, because a larger hormone pulse, a diagnostic result and a sustained treatment benefit answer different questions. The strongest findings reviewed here concern measured hormones and eating behavior; long-term changes in strength, body composition or recovery require further outcome evidence.
Overview
GHRP-2 contains D-amino acids and a naphthylalanine building block within an amidated peptide. The pharmaceutical preparation pralmorelin hydrochloride is described as a dihydrochloride in the Japanese regulatory dossier. The salt and the peptide core should remain explicitly identified when comparing chemical records. PMDA application dossier, Doi et al.
Molecular profile
Forms and derivatives
Pralmorelin hydrochloride (KP-102)
The dihydrochloride preparation described in the Japanese pharmaceutical development record. Its diagnostic setting concerns supervised measurement of GH reserve.
GHRP-2 plus GHRH
A distinct paired stimulus used in endocrine experiments. Responses depend on pituitary reserve, physiological state and the actual combination tested.
Its numbered name distinguishes it from GHRP-6, which has a different sequence. The number “2” is part of the compound’s name; it does not describe the number of amino acids or a universal potency ranking.
Uses and research areas
The endocrine studies used GHRP-2 to test GH secretion in children with different causes of short stature, adults with suspected GH deficiency and people whose hormone axis was altered by prolonged critical illness. Japan’s pralmorelin development concerns diagnosis of impaired GH secretion. The validation study by Chihara and colleagues compared healthy participants with patients already classified by an insulin tolerance test, illustrating how a provoked response can help assess pituitary reserve.
Appetite research asked a separate question: whether a synthetic ghrelin agonist made people eat more at a laboratory meal. That effect appeared in lean participants and participants with obesity. Its relevance depends on the intended outcome. An increase in intake may be useful to investigate appetite biology or deficient nutrition, while durable weight change and functional benefit need longer studies. Laferrère et al., 2005, Laferrère et al., 2006
Mechanism of action
The ghrelin receptor GHS-R1a provides a connection between hormone release and appetite. In the pituitary and hypothalamic system, GHRP-2 supplies a stimulus that works alongside GHRH, the hypothalamic GH-releasing hormone. GH is secreted in pulses, and the size of a measured response depends on available pituitary reserve, hypothalamic signaling, feedback and the participant’s physiological state.
The hormone response can extend beyond GH. The controlled meal experiment in healthy men recorded a transient cortisol rise, and animal comparisons have found ACTH and cortisol stimulation with GHRP-2. ACTH is the pituitary signal that stimulates adrenal cortisol production. These observations are relevant to the material’s endocrine selectivity and to the interpretation of repeated exposure. Laferrère et al., Raun et al.
The influence of body composition is especially visible in stimulation studies. Paulo and colleagues studied twelve healthy young men with normal gonadal function and ten with experimentally reduced sex-steroid levels, using separate paired-secretagogue tests. Higher BMI was associated with smaller peak responses in the normally gonadal group, while sex-steroid reduction attenuated responses in lean men. The study tested determinants of hormone secretion; it offers no estimate of a body-composition benefit from treating those men.
Pharmacokinetics
The reviewed source set does not provide a sufficiently documented intact-peptide human elimination half-life for a GHRP-2 concentration illustration. Many GHRP-2 experiments measured GH after intravenous stimulation or during subcutaneous infusion. A hormone-response curve includes secretion, physiological feedback and GH clearance, so its decline cannot identify GHRP-2 elimination.
Johansen and colleagues directly compared peptide pharmacokinetics in male rats. After intravenous administration, peptide concentrations in blood declined in two phases. After nasal administration, about 50% of GHRP-2 and the experimental peptides NNC 26-0194 and NNC 26-0235 reached circulation, compared with about 20% of ipamorelin. The study reported somewhat lower nasal absorption for GHRP-6 than for GHRP-2 and the two NNC peptides. That study establishes that route and sequence affect exposure. A nasal absorption percentage obtained in a rat preparation does not supply the missing human exposure profile.
Research findings
A controlled meal response in healthy men
In the randomized, double-blind crossover 2005 study, seven lean healthy men received subcutaneous GHRP-2 infusion and saline on separate 270-minute visits. A buffet-style meal allowed investigators to weigh food consumed. Average intake increased by 35.9% ± 10.9%, with every participant eating more; the proportions of carbohydrate, fat and protein remained similar. GH rose markedly, cortisol rose transiently and no infusion side effects were reported. The within-person design supports an acute appetite effect, while its small sample and one-meal endpoint leave sustained nutritional benefit unresolved.
The 2006 crossover study extended the comparison to nineteen healthy, weight-stable participants: ten lean and nine with obesity. Across three visits they received placebo and two active exposure conditions, with a fixed breakfast followed by a freely chosen buffet lunch. Intake increased by 10.2% ± 3.9% and 33.5% ± 5.8% at the two active levels. Obesity status did not alter the food-intake response. The hormone figure used a smaller analyzed subset, so the meal denominator should not be assigned to every endocrine measurement.
Pituitary reserve and diagnostic context
Tuilpakov and colleagues compared intravenous GHRP-2, GHRH(1–29)-NH2 and their combination in randomized order in ten children with GH insufficiency and five with idiopathic short stature. Responses to the single peptides were generally low in the insufficiency group and substantially larger in the idiopathic group during ninety-minute sampling. One GHRP-2 comparison included nine children from the insufficiency group. The accessible abstract ends before a complete account of the combination results, so this profile retains the diagnostic-group finding without reconstructing the missing conclusion.
An adult diagnostic validation study enrolled 77 healthy subjects and 58 patients with severe GH deficiency classified by insulin tolerance testing. It recorded lower stimulated GH in the patient group and favorable repeatability. The paper also specified different cutoffs depending on the GH calibration standard. Those assay-specific thresholds illustrate why interpretation belongs to a defined diagnostic method and laboratory, beyond simply comparing a blood value with an online number.
Endocrine responses during prolonged critical illness
Van den Berghe and colleagues assigned twenty-six critically ill adults to four crossover comparison sets. Ten contributed to placebo versus GHRP-2; the other sets compared GHRH, GHRP-2 and combined stimulation. The infusions lasted about twenty-one hours, spanning overnight hormone sampling. GHRP-2 increased GH secretion and serum IGF-I within twenty-four hours, with further stimulation when GHRH was added. Elevated cortisol remained unchanged in this population. The endpoints establish short endocrine responsiveness during severe illness. Recovery, muscle function and survival were not established by those measurements.
Safety and tolerability
GHRP-2 has no FDA-approved therapeutic indication. Pralmorelin’s Japanese diagnostic context is a separate jurisdiction and purpose: a supervised provocative test supplies information about GH reserve. It should not be converted into evidence that chronic use improves muscle growth or healthy aging. PMDA dossier
FDA flags possible immune reactions from aggregation and peptide-related impurities in injectable and nasal compounded GHRP-2. The agency also notes reports of increased insulin requirement, infection, pancreatitis and deaths in critically ill subjects, with causality unestablished. These reports require careful clinical interpretation because underlying disease and concurrent treatments can produce the same events. FDA compounding safety assessment
The controlled meal studies were brief, while the critical-illness experiment involved severely altered physiology. Neither setting resolves uncommon harms or long-term effects of GH/IGF signaling, stress-axis activation and increased appetite. The small study reporting no infusion side effects provides useful acute tolerability information within its own conditions.
What the research means
GHRP-2 is a useful example of how one receptor family can influence several outcomes at once. Human studies show that GH release and eating behavior both respond to the peptide. Diagnostic work then demonstrates that a weak response can carry information about impaired pituitary function, while BMI and gonadal state help explain variation between participants.
For a proposed treatment benefit, the next evidentiary step is the outcome itself: sustained nutrition, strength, body composition, symptom relief or recovery, measured against an appropriate comparison over a relevant duration. The reviewed meal and hormone experiments establish the biological premise, and leave those longer clinical questions open.
FAQs
Does GHRP-2 increase appetite in people?
Controlled crossover experiments found greater buffet-meal intake during GHRP-2 exposure, including in participants with obesity. These visits establish an acute eating response. Sustained nutrition, weight change and functional outcomes require longer trials. Laferrère et al.
How is a GH stimulation test different from treatment?
A stimulation test measures the pituitary’s capacity to release GH after a defined challenge. The diagnostic study compared participants with established severe GH deficiency with healthy subjects and used assay-specific interpretation. A chronic treatment study would instead need to measure the intended clinical benefit and harms over time. Chihara et al.
Why does the same stimulus produce different hormone responses?
Pituitary reserve, hypothalamic signals, feedback, adiposity and sex-steroid availability influence the GH response. Experiments comparing different participant groups help explain that variation. A larger pulse in one setting does not establish a larger functional benefit. Paulo et al.
Can the GH curve reveal GHRP-2 half-life?
The measured GH curve follows a hormone released in response to GHRP-2. Its rise and fall depend on pituitary secretion, hormonal feedback and removal of GH from blood. Measuring how quickly GHRP-2 itself disappears requires an assay for that peptide. The reviewed human sources did not establish the intact-peptide measurement needed for a half-life illustration.
Comparisons and related reading
GHRP-6 and hexarelin provide related endocrine experiments, while ipamorelin adds a distinct selectivity comparison and postoperative clinical programme. Sermorelin engages the GHRH pathway, helping explain why two secretagogues can interact despite different receptor targets.
References
Randomized-order childhood stimulation tests distinguish GH insufficiency from idiopathic short stature.
Male-rat direct peptide measurements show route- and compound-dependent exposure.
Seven healthy men received subcutaneous GHRP-2 infusion and saline on separate visits. Investigators weighed buffet food consumed; participants ate more during GHRP-2 exposure.
A larger crossover meal study found dose-dependent intake responses in lean and obese participants.
Short infusions changed GH and IGF-I during prolonged critical illness across distinct comparison sets.
Paired-secretagogue experiments link BMI and experimental sex-steroid withdrawal to GH responsiveness.
An animal comparator study records accompanying ACTH and cortisol responses to GHRP-2.
The original pharmacology paper identifies the modified peptide and dihydrochloride preparation.
The diagnostic comparison reports reproducibility and calibration-dependent interpretation of provoked GH.
The dossier specifies the dihydrochloride chemistry and diagnostic purpose.
The agency identifies substance- and route-specific safety concerns and gaps for compounded peptides.
Glossary
- Secretagogue
- A compound that stimulates release of a substance already produced by a cell.
- Ghrelin
- A peptide signal involved in GH secretion, appetite and other physiological processes.
- GHS-R1a
- The ghrelin receptor subtype involved in GH-secretagogue signaling.
- Pituitary reserve
- The capacity of pituitary cells to release a hormone after a defined stimulus.
- IGF-I
- Insulin-like growth factor I, a downstream mediator influenced by GH and metabolic state.
- Crossover trial
- A study in which participants receive different comparison conditions during separate periods.
- Gonadal state
- The functional state of the reproductive-hormone system.