GHRP-2: The Growth Hormone Secretagogue That Became a Diagnostic Drug

Most research peptides live their whole lives in laboratories. GHRP-2 escaped. A molecule that started as a curiosity in an American endocrinology lab ended up in hospital clinics in Japan, where doctors use it to answer one of the trickiest questions in hormone medicine: is this patient’s pituitary gland still able to make growth hormone? It is one of the very few compounds in any research catalogue that has made that journey from bench to clinic.

This article tells that story. It explains why diagnosing growth hormone deficiency is so difficult, why GHRP-2 turned out to be such a good tool for the job, what the validation studies found, and the surprising places the peptide has turned up since, from intensive care units to thyroid tumours. For the full background on GHRP-2’s chemistry and wider research, see our GHRP-2 research guide. Crown Peptides supplies GHRP-2 for laboratory research use only.

The Problem GHRP-2 Solved: You Cannot Just Measure Growth Hormone

If a doctor suspects someone’s thyroid is underactive, they order a blood test for thyroid hormone. Simple. Growth hormone does not work like that, and understanding why is the key to this whole story.

A hormone that comes in bursts

Growth hormone is released from the pituitary gland in pulses, a handful of large bursts across the day and night, most prominently during deep sleep. Between those bursts, blood levels can fall almost to zero, even in a perfectly healthy person. A single blood sample taken at a random moment tells you very little: a low reading might mean the pituitary is failing, or it might just mean the sample was taken between pulses.

The answer: provoke it

Endocrinologists solve this with stimulation tests, also called provocative tests. They give the patient something that should make a healthy pituitary release a large burst of growth hormone, then take blood samples over the following hour or two. A healthy gland responds with a big peak. A failing gland produces little or nothing. The size of the peak is what makes the diagnosis.

The trouble with the gold standard

For decades, the international first-choice stimulation test has been the insulin tolerance test. Insulin is used to deliberately drive blood sugar down to a low level, a stress that makes the pituitary release growth hormone and cortisol. It is accurate, but it is unpleasant and carries real risk. Deliberately inducing low blood sugar can cause sweating, confusion and, in vulnerable patients, seizures or heart problems. It is unsuitable for people with heart disease, epilepsy and some other conditions, and it needs close medical supervision.

That created a clear need for a safer alternative that was still reliable. Several were tried, including arginine and glucagon, and combinations with GHRH. In Japan, GHRP-2 became one of the leading candidates.

A crowded field of stimuli

Over the years, endocrinologists have tried a remarkable range of substances to provoke growth hormone release. Arginine, an amino acid, works partly by suppressing somatostatin. Glucagon, a hormone normally involved in raising blood sugar, triggers growth hormone release through a slower, less direct route and needs several hours of sampling. Clonidine, a blood pressure medicine, has been used particularly in children. GHRH itself, combined with arginine, became a widely used alternative in Europe. Each option has its own balance of reliability, convenience, duration and side effects, and none is perfect.

Against that backdrop, GHRP-2 offered an attractive combination: a strong response that was relatively resistant to the somatostatin brake, a short test lasting around an hour, and no need to drive blood sugar dangerously low. That combination is why it found a lasting place in Japanese practice.

From Curiosity to Candidate

GHRP-2 belongs to a family of synthetic peptides first developed in the late 1970s and 1980s, largely through the work of the American endocrinologist Cyril Bowers. His early experiments with modified fragments of met-enkephalin, one of the body’s own opioid peptides, revealed synthetic molecules that released growth hormone through a receptor nobody had yet identified. GHRP-6 came first; GHRP-2 followed as a more potent member of the family.

The receptor, now called the ghrelin receptor, was cloned in 1996, and its natural hormone, ghrelin, was discovered in 1999. By then, GHRP-2 was already being developed clinically in Japan, where it is known by its drug name, pralmorelin, and development code KP-102.

Why potency makes a good diagnostic

A stimulation test only works if the stimulus is strong and consistent enough that a healthy pituitary always responds clearly. GHRP-2 turned out to be ideal. In a 2004 pharmacological study in Arzneimittelforschung, the Japanese developer reported that in conscious rats, GHRP-2 released growth hormone more potently than injected GHRH, and it still worked in conscious dogs where GHRH did not raise growth hormone at all (PMID: 15646370). The authors concluded that GHRP-2 was less sensitive to suppression by somatostatin, the body’s natural brake on growth hormone. For a diagnostic test, that resilience is exactly what you want: a signal that a healthy pituitary will answer loudly, whatever else is going on.

The Validation Study That Made It a Standard Test

A diagnostic test needs proof. The key study was published in 2007 in the European Journal of Endocrinology by Chihara and colleagues on behalf of the KP-102 Study Group (PMID: 17609397).

How the study was designed

The researchers enrolled 77 healthy volunteers and 58 patients already known to have severe growth hormone deficiency, confirmed by the insulin tolerance test. Everyone received GHRP-2 after an overnight fast, and blood samples were taken over the following two hours.

What they found

The results were about as clear-cut as diagnostic research gets. In every single participant, growth hormone peaked within 60 minutes. In the healthy group, the average peak was 84.6 micrograms per litre. In the patients with growth hormone deficiency, it was just 1.36. That is a difference of more than sixty-fold. The response was not affected by sex, and although it was slightly lower in older people and in those carrying more body fat, those differences did not change the diagnosis. Repeat testing showed good reproducibility, and the test worked equally well whether the underlying problem lay in the hypothalamus or the pituitary.

Setting the cut-off

From these data, the researchers defined a cut-off peak growth hormone value below which severe deficiency could be diagnosed with high reliability, and showed that it corresponded to the established cut-off for the insulin tolerance test. That cut-off was later expressed against the World Health Organization’s recombinant growth hormone reference standard, and a 2014 review of adult growth hormone deficiency in Neurologia Medico-Chirurgica described the GHRP-2 test as an established diagnostic method in Japan (PMID: 25070016, PMC4533495).

How GHRP-2 Compares With Other Stimulation Tests

Once the GHRP-2 test was established, researchers began comparing it head to head with the alternatives.

Against the insulin tolerance test and arginine

In a 2013 study in Endocrine Journal, Kinoshita and colleagues at Hiroshima University gave all three tests, the insulin tolerance test, the arginine test and the GHRP-2 test, to 71 adults with pituitary tumours before surgery (PMID: 23079545). Peak growth hormone responses were significantly higher with GHRP-2 than with the other tests, reflecting how powerful a stimulus it is. The authors concluded that both the arginine and GHRP-2 tests were acceptable alternatives to the insulin tolerance test for diagnosing adult growth hormone deficiency in Japanese patients, while noting that diagnostic criteria should be adjusted to each population.

A second job: checking the stress hormone axis

GHRP-2 does not only release growth hormone. It also stimulates ACTH and cortisol through the hypothalamic-pituitary-adrenal axis. For most research this is a side effect, but diagnosticians saw an opportunity: the insulin tolerance test is also used to check whether the adrenal stress-hormone system works, so could GHRP-2 do that job too?

In a 2018 study in the Journal of the Endocrine Society, Hayakawa and colleagues at Osaka University analysed 254 patients who had undergone both tests (PMID: 30324179, PMC6055535). Across the whole group, peak cortisol values correlated strongly between the two tests, though the GHRP-2 test was not suitable for everyone because factors such as sex and certain pituitary tumours influenced the response. In men without a hormone-producing pituitary tumour, the GHRP-2 test showed 95% sensitivity and 85% specificity, and the authors concluded it could replace the insulin tolerance test for assessing the adrenal axis in that group. It is a nice example of turning a so-called side effect into a useful tool.

In children and adolescents

Growth hormone testing in young people has its own challenges, and GHRP-2 has been studied here too. In a 2010 study in the Journal of Pediatric Endocrinology and Metabolism, Asakura and colleagues at Kanagawa Children’s Medical Center gave the GHRP-2 test to 56 children with growth disorders and compared it with the insulin tolerance test (PMID: 20662346). Peak growth hormone values correlated strongly between the two tests, and the authors concluded that the GHRP-2 test was safe, took an hour or less, and was capable of diagnosing growth hormone deficiency in children.

Later work has continued to refine the test in young people. A 2024 report in the Journal of Pediatric Endocrinology and Metabolism from Niigata University looked at adolescents who had undergone the GHRP-2 test and found robust growth hormone responses in those without an organic or genetic cause of deficiency (PMID: 38958228). Because the response was so strong, the authors suggested the cut-off for adolescents may need revisiting to avoid missing some cases, showing how the test continues to be refined.

Beyond Diagnosis: The Unexpected Places GHRP-2 Has Turned Up

A compound that reliably wakes up the growth hormone system is useful for more than diagnosis. GHRP-2 has been explored in several striking research settings.

Waking up the hormones of the critically ill

Patients who spend a long time in intensive care often develop a strange hormonal state: their growth hormone, thyroid and reproductive hormone systems all become suppressed at the level of the brain, while their bodies break down muscle and bone at an alarming rate. The Belgian intensive care researcher Greta Van den Berghe, working with Cyril Bowers and others, investigated whether reactivating those hormone systems could help.

The work began with a question about cause. If the pituitary itself were damaged by critical illness, stimulating it would achieve little. In a 1998 study in the Journal of Clinical Endocrinology and Metabolism, Van den Berghe and colleagues gave overnight infusions of TRH, GHRP-2 and GHRH, alone and in combination, to 20 adults who had been critically ill for several weeks (PMID: 9467533). The results were striking. GHRP-2 amplified pulsatile growth hormone secretion more than six-fold, and more than ten-fold when combined with GHRH, raising IGF-1 and its binding proteins substantially within about two days. Adding TRH raised thyroid hormones. The pituitary was clearly still capable of responding; the problem lay upstream, in the brain’s signalling. That insight reframed how researchers understood the hormonal collapse of long-term critical illness.

An orchestra brought back into time

The Leuven group then noticed something subtler. In healthy people, the pituitary’s release of growth hormone, TSH and prolactin is loosely synchronised, the hormones rising and falling together. In critically ill patients that coordination was lost. In a 1999 study in the European Journal of Endocrinology, the team analysed 86 overnight hormone profiles and found that GHRP-2 infusion, but not GHRH or TRH, markedly re-synchronised the release of all three hormones (PMID: 10037246). The authors suggested that the body’s own ghrelin-like signal may help orchestrate coordinated pituitary hormone release, a remarkable idea that emerged directly from studying GHRP-2.

Adding the other hormone systems

In a 2002 randomised study in Clinical Endocrinology, 33 men with prolonged critical illness received five days of placebo, GHRP-2 alone, GHRP-2 with thyrotropin-releasing hormone (TRH), or GHRP-2 with TRH plus pulses of gonadotropin-releasing hormone (PMID: 12030918). GHRP-2 on its own reactivated growth hormone secretion and normalised IGF-1 and related binding proteins. Adding TRH brought thyroid hormones back to normal within a day. Only the triple combination also reactivated the reproductive axis, raised testosterone substantially and produced the broadest metabolic effects, including reduced protein breakdown. The authors concluded that correcting several hormonal deficits together was key to counteracting the body’s breakdown state in prolonged critical illness. It remains one of the most elegant human studies of the growth hormone axis ever carried out.

Revealing hidden pituitary tumours

In healthy people, GHRP-2 does not raise thyroid-stimulating hormone (TSH). A Japanese team wondered whether that might change in patients with rare TSH-producing pituitary tumours. In a 2018 study in Endocrine Journal, Kageyama and colleagues found that two of five such patients showed a significant TSH rise in response to GHRP-2, and in one patient whose tumour was removed completely, the response disappeared (PMID: 29973439). It is a small study, but it shows how a well-understood stimulus can expose abnormal behaviour in a diseased gland.

Studying hunger in people

Because GHRP-2 acts at the ghrelin receptor, researchers have also used it to study appetite. In a 2005 study in the Journal of Clinical Endocrinology and Metabolism, Laferrère, Bowers and colleagues found that healthy men given a GHRP-2 infusion ate 35.9% more at a buffet meal than when given saline, with every participant increasing their intake (PMID: 15699539, PMC2824650). The authors described GHRP-2 as a valuable tool for investigating ghrelin’s effects on eating behaviour in humans.

What the Diagnostic Story Tells Researchers

GHRP-2’s clinical career is not just an interesting piece of history. It shapes how the compound is understood and used in research today.

A uniquely well-characterised response

Because the GHRP-2 test has been validated in large groups of healthy people and patients, researchers know unusually well what a normal growth hormone response to GHRP-2 looks like, how it changes with age and body composition, and how reproducible it is. Few research peptides come with that kind of reference data.

A clear picture of its other effects

The diagnostic literature has also mapped GHRP-2’s effects on ACTH, cortisol, prolactin and TSH in real patients. For researchers, that is a detailed guide to which hormone systems may move alongside growth hormone in any experiment.

A model for how peptides reach the clinic

GHRP-2’s path, from a synthetic curiosity studied for its effect on a then-unknown receptor, through careful pharmacology and validation, to a role in everyday clinical practice, is a textbook example of how laboratory peptide research can end up changing medicine.

The Technical Breakdown: How GHRP-2 Triggers Such a Strong Response

This section explains the mechanism in more detail for readers who want it.

The molecule

GHRP-2 is a six-building-block peptide, usually written D-Ala-D-2-Nal-Ala-Trp-D-Phe-Lys-NH2. Several of its building blocks are D-amino acids, the mirror-image forms of the natural L-amino acids, which resist the enzymes that normally break down peptides. D-2-naphthylalanine, with its large double-ring side chain, is thought to be important for locking into the receptor. The amidated lysine at the end protects against enzymes that attack from the tail.

Two sites of action

GHRP-2 acts at two levels. At the pituitary, it binds the ghrelin receptor on growth hormone-producing somatotroph cells and triggers release directly. At the hypothalamus, it increases release of the body’s own GHRH and reduces somatostatin. The 2004 pharmacology study showed both matter: GHRP-2 still worked when the hypothalamus was disconnected, but produced less growth hormone, confirming that its full effect depends on amplifying the brain’s own signal.

The signalling cascade

The ghrelin receptor mainly activates a Gq protein, which switches on phospholipase C. That generates IP3, releasing calcium from stores inside the cell, and diacylglycerol, activating protein kinase C. The resulting surge in intracellular calcium drives the release of growth hormone granules. Because this route differs from the cyclic AMP route used by the GHRH receptor, GHRP-2 and GHRH work synergistically when combined.

Why it resists the somatostatin brake

Somatostatin inhibits growth hormone release partly by opposing the cyclic AMP pathway used by GHRH. GHRP-2’s calcium-based route and its ability to suppress somatostatin release at the hypothalamus both help explain why it keeps working in conditions where GHRH alone is blunted. That property is precisely what makes it so dependable as a diagnostic stimulus.

Why it also moves ACTH and cortisol

GHRP-2’s effect on the stress hormone axis is thought to involve activation of hypothalamic pathways that drive ACTH release, possibly including corticotropin-releasing hormone and vasopressin. Newer compounds such as Ipamorelin were designed specifically to avoid this effect.

Why Verification Matters for a Compound Like GHRP-2

A diagnostic test depends on the stimulus being exactly what it claims to be. The same is true in the laboratory.

GHRP-2 contains several D-amino acids, so a version synthesised with the wrong stereochemistry at one position would have exactly the same mass but different behaviour. And GHRP-2 has a documented history of lookalikes in unregulated markets. In 2018, anti-doping scientists in Cologne reported black market products containing a glycine-extended version of GHRP-2, with one extra amino acid at the front (PMID: 29864719). A 2019 study from Warsaw described identifying another glycine analogue of GHRP-2 in a seized injection vial using high-resolution mass spectrometry. Only mass spectrometry reliably catches changes like these, while HPLC is needed to measure purity and separate related impurities.

The Crown Peptides standard

Every batch of GHRP-2 supplied by Crown Peptides comes with a batch-specific certificate of analysis showing HPLC purity and mass spectrometry identity confirmation, with lot numbers matching those on vial labels. Published certificates are on our Lab Reports page. Our guides to peptide testing and reading a certificate of analysis explain the methods.

Handling

GHRP-2 is supplied as a lyophilised powder and should be stored cold, dry and away from light. Our guides to peptide reconstitution and how long peptides last cover the practical side, and Bacteriostatic Water is available alongside.

Related Compounds in the Growth Hormone Family

GHRP-2 has close relatives on both sides of the growth hormone system.

The other ghrelin receptor agonists

GHRP-6 is GHRP-2’s older sibling, known for a stronger appetite effect; see GHRP-2 vs GHRP-6. Ipamorelin was designed to release growth hormone without GHRP-2’s effects on ACTH and cortisol; see Ipamorelin vs GHRP-2.

The GHRH analogues

Sermorelin, itself once an FDA-approved diagnostic agent in the US, along with Tesamorelin and CJC-1295 with DAC, act on the GHRH receptor. The CJC-1295 (No DAC) + Ipamorelin (Blend) combines both receptor pathways. Our comparison CJC-1295 vs Sermorelin tells Sermorelin’s own diagnostic story.

Downstream

IGF-1 LR3 lets researchers study the downstream hormone directly. Browse the full group in our endocrine and hormonal research peptides category.

GHRP-2 Diagnostic Questions, Answered

Is GHRP-2 an approved drug?

As pralmorelin, GHRP-2 is used in Japan as a diagnostic agent for growth hormone deficiency. It is not a licensed medicine in the UK, where it is available as a research material.

Why is GHRP-2 used instead of the insulin tolerance test?

Because the insulin tolerance test works by deliberately inducing low blood sugar, which is unpleasant and unsuitable for some patients. GHRP-2 provides a strong, reproducible growth hormone stimulus without that stress, and validation studies found it diagnosed severe deficiency reliably.

How strong is the growth hormone response to GHRP-2?

Very strong. In the 2007 validation study, healthy people had an average peak more than sixty times higher than patients with severe growth hormone deficiency, and the response was higher than with the insulin tolerance test or arginine in a later comparison.

Can GHRP-2 test the adrenal system too?

A 2018 study found that in men without a hormone-producing pituitary tumour, the GHRP-2 test assessed the adrenal stress-hormone axis with high sensitivity and specificity compared with the insulin tolerance test.

How long does the GHRP-2 test take?

The published protocols take around an hour to two hours of blood sampling. In the 2007 validation study, growth hormone peaked within 60 minutes in every participant, which is one reason the test is regarded as quick and practical compared with some alternatives.

What is the difference between GHRP-2 and pralmorelin?

None. Pralmorelin is the drug name for GHRP-2. You will also see it called KP-102 in Japanese research papers.

From Curiosity to Clinic, and Back to the Lab

GHRP-2 began as one of a family of odd synthetic peptides that released growth hormone through a receptor nobody could find. Decades later, it sits in hospital protocols in Japan, trusted to tell doctors whether a patient’s pituitary still works, and it has helped researchers reawaken the hormone systems of critically ill patients, uncover rare pituitary tumours and study the biology of hunger. Few research compounds have such a detailed human track record.

For researchers, that record is a gift: a stimulus whose effects on the growth hormone system, and on the hormones that move alongside it, have been mapped in real patients. Explore GHRP-2 from Crown Peptides, every batch HPLC and mass spectrometry verified and dispatched from the UK.