GHRP-2 vs GHRP-6: differences, evidence and safety

Verdict: GHRP-2 (pralmorelin) has the deeper human record: controlled trials and a diagnostic role in Japan. GHRP-6 has older human hormone studies and one phase 3 stroke trial that missed its main goal. Neither is FDA approved, both sit in FDA compounding Category 2, and WADA prohibits both.

GHRP-2 vs GHRP-6 compares two synthetic growth hormone-releasing peptides (GHRPs), short lab-made peptides that switch on the ghrelin receptor (GHS-R1a) and make the pituitary release growth hormone (GH). The strongest evidence for GHRP-2 is a double-blind randomized trial in 19 lean and obese adults showing that it raises hunger and food intake [Human RCT, n=19]. The strongest evidence for GHRP-6 is the COURAGE-2 phase 3 stroke trial, where GHRP-6 was given together with epidermal growth factor (EGF) and did not beat standard care on its primary endpoint [Human RCT, open-label, n=188]. No trial has compared the two peptides head to head in people, and neither has shown gains in muscle or strength in a human trial.

Item	GHRP-2	GHRP-6
US FDA status	Not approved for any use	Not approved for any use
Compounding (503A/503B)	Category 2 (503B), since 2023-09-29	Category 2 (503B), since 2023-09-29
WADA 2026	Prohibited at all times, S2.2.4	Prohibited at all times, S2.2.4
Strongest evidence	Human RCT (n=19), appetite; diagnostic validation (n=135)	Phase 3 RCT with EGF (n=188), primary endpoint missed
Human trials	None registered on ClinicalTrials.gov; small published studies (n=6 to 135)	None registered on ClinicalTrials.gov; stroke trials registered in Cuba
Main risk signal	FDA cites higher insulin needs, deaths of critically ill study subjects, infection, pancreatitis	FDA cites cortisol effects and higher blood glucose
Last checked	2026-10-01	2026-10-01

GHRP-2 vs GHRP-6 at a glance

Feature	GHRP-2	GHRP-6
What it is	Synthetic hexapeptide with an unnatural amino acid (D-β-naphthylalanine); also called pralmorelin or KP-102	Synthetic hexapeptide: His-D-Trp-Ala-Trp-D-Phe-Lys-NH2
Class	GH-releasing peptide, ghrelin mimetic	GH-releasing peptide, ghrelin mimetic
Receptor	GHS-R1a	GHS-R1a
Main research focus	GH deficiency testing, short stature, critical illness, appetite	GH physiology, sleep, heart and stroke injury
Human evidence	Small RCTs and uncontrolled studies; diagnostic validation	Small hormone studies; one phase 1/2 and one phase 3 stroke trial (with EGF)
Approval status	None (FDA); used as a diagnostic test in Japan	None (FDA)
WADA	S2.2.4, prohibited	S2.2.4, prohibited
Routes studied	Intravenous, under the skin, intranasal	Intravenous, oral, intranasal, sublingual
Half-life in people	About 0.55 h (children, IV)	About 2.5 h (men, IV)
Timelines in studies	GH peak within 60 min of an IV dose	GH peak 60 to 75 min after an oral dose
Main safety concerns	Prolactin, ACTH and cortisol rise; hunger; FDA immunogenicity and serious-event reports	Cortisol rise; blood glucose; FDA immunogenicity concerns

What is GHRP-2?

GHRP-2, listed by WADA as pralmorelin, is a six-amino-acid synthetic relative of GHRP-6. Italian researchers described it as a synthetic “super-analog” of GHRP-6 that strongly releases GH in people [Human, n=12]. Under the code KP-102, a Japanese study group validated it as a one-injection test for adult GH deficiency in 135 people, and Japanese hospitals still use the GHRP-2 test to evaluate GH secretion. It has also been tested in children with short stature and in intensive care patients. It is not an FDA-approved drug for any use.

What is GHRP-6?

GHRP-6 is the original growth hormone-releasing peptide. Cyril Bowers and colleagues described it in 1984 as a hexapeptide that releases GH in rats, monkeys, lambs and calves [Animal]. Work with GHRP-6 and its relatives led, according to Bowers’ own history of the field, to the identification of the GHS receptor in 1996 and the discovery of ghrelin, the body’s own hunger hormone, in 1999. In 18 healthy men, it was a potent GH releaser that worked synergistically with GHRH [Human, n=18]. A Cuban research center has since tested it for heart and stroke injury. It is not FDA approved.

How they work differently

Both peptides bind the same receptor, so most differences are in strength, side hormones and how long they last.

• GHRP-2: in sheep pituitary cells, it raised the signaling molecule cAMP the way GHRH does, while GHRP-6 did not; in rat cells GHRP-2 did not raise cAMP, so the difference may vary by species [Lab].
• GHRP-6: in healthy men, small doses combined with GHRH released more GH than either alone; prolactin and cortisol rose about twofold only at the highest dose tested [Human, n=18].
• GHRP-2: raised prolactin, ACTH and cortisol at every dose tested in young adults, though its prolactin effect was weaker than that of TRH [Human, n=6]. In critically ill adults, a 21-hour infusion did not change their already high cortisol levels [Human RCT, crossover, n=26].
• GHRP-6: repeated IV doses at night raised GH, ACTH and cortisol and increased light (stage 2) sleep without changing deep sleep [Human, placebo-controlled].
• GHRP-6: taken by mouth, it worked but with about 0.3% of the IV activity [Human, n=5 men and 9 children]. Enteric-coated oral capsules taken at night did not change GH, ACTH or cortisol, while the nasal form raised GH [Human].

Evidence head-to-head

Each cell gives the best evidence found for that outcome and its level.

Outcome	GHRP-2 best evidence	GHRP-6 best evidence
Acute GH release	Human: strong GH peak in 77 healthy adults	Human: dose-related GH peak in 18 men
IGF-1 over weeks	Human: IGF-1 held higher over a 30-day infusion (n=17, older adults)	No study of GHRP-6 alone found
Appetite and food intake	Human RCT: intake up 33.5% at the higher rate (n=19)	Animal: eating triggered in rats
Growth in children	Human, uncontrolled: growth rate up (n=15); IGF-1 unchanged	Human: acute GH response only (9 children)
Diagnosing GH deficiency	Human: validated against the insulin test (n=71)	Human: GHRH plus GHRP-6 test failed in severely obese men (n=26)
Critical illness	Human RCT: GH and IGF-1 restored (n=33); no outcome benefit shown	No human study found
Stroke	No study found	Human RCT with EGF: primary endpoint missed (n=188)
Heart attack injury	No study found	Animal: smaller infarcts in pigs
Muscle, strength, fat loss	No human trial	No human trial

Two points stand out. First, the outcome people most often ask about, muscle gain, has no human trial for either peptide. Second, the main practical difference repeated online (GHRP-6 for hunger, GHRP-2 for less hunger) has never been tested head to head; the only controlled human appetite data belong to GHRP-2, and they show a clear rise in food intake [Human RCT, n=19].

Which fits which goal?

• GH testing: GHRP-2 has more evidence. A validation study in 77 healthy adults and 58 patients separated GH deficiency from normal function with good reproducibility [Human, n=135], and a study in 56 children found it diagnosed GH deficiency within an hour [Human, n=56].
• Raising appetite: GHRP-2 has more human evidence, from two controlled feeding studies [Human, n=7 and n=19]. GHRP-6 has animal evidence only.
• Sustained GH and IGF-1: GHRP-2 has more evidence, from 30 days of continuous infusion in older adults [Human, n=17]; in GH-deficient children, injections raised GH briefly but did not raise IGF-1 over eight months [Human, n=6].
• Tissue protection after stroke or heart injury: GHRP-6 has more evidence, though mixed: a phase 1/2 trial reported better recovery with EGF plus GHRP-6 [Human RCT, open-label, n=36], but the larger phase 3 did not confirm it overall.

These are statements about evidence, not reasons to use either peptide. A clinician is the person to decide whether any GH-axis treatment fits a given person.

Can they be combined?

In sheep pituitary cells, GHRP-2 and GHRP-6 at maximal doses had an additive effect on GH release [Lab]. The only human data on using them together come from a retrospective chart review of men on testosterone therapy who were prescribed GHRP-2, GHRP-6 and the GHRH analogue sermorelin at the same time: in the 14 who met the inclusion criteria, mean IGF-1 rose from 159.5 to 239.0 ng/mL [Human, observational, n=14]. That review had no control group, mixed three peptides, and did not measure muscle or fat outcomes. Online, GHRPs are also often paired with GHRH analogues such as CJC-1295, which we cover in our evidence review of the Joe Rogan peptides. No controlled human study has tested GHRP-2 and GHRP-6 together.

Safety and regulatory status

United States (FDA): neither peptide is an approved drug. FDA placed both in compounding Category 2 for 503B outsourcing facilities on 2023-09-29, meaning they may present significant safety risks. For GHRP-2, FDA cites possible immune reactions from aggregation and impurities, and reports of “increased insulin requirement to maintain the blood glucose level, death of critically ill study subjects, infection and pancreatitis.” For GHRP-6, it cites immunogenicity, a “potential effect on cortisol and increase in blood glucose due to decreases in insulin sensitivity.”

Sport (WADA): both are named in the 2026 Prohibited List under S2.2.4, growth hormone releasing factors, and are banned in and out of competition. Doping laboratories have published urine methods for GHRPs and their metabolites.

Japan: GHRP-2 is used to evaluate GH secretion in hospital endocrinology, as a single diagnostic test.

Side effects seen in studies:

• GHRP-2 infused for five days in critically ill men raised blood lactate and white cell counts, and on its own did not reduce protein breakdown [Human RCT, n=33].
• In the GHRP-6 stroke trial, serious adverse events occurred in 30 of 95 treated patients versus 18 of 93 controls; investigators judged none treatment-related, and the difference was not statistically significant [Human RCT, n=188].
• When the GH receptor was blocked, a single GHRP-6 dose raised insulin and glucose, a sign of GH-independent effects on metabolism [Human, n=10].
• A 2026 clinical review of people self-injecting GH-axis peptides lists prolactin and cortisol rises, appetite changes, blood sugar problems, fluid retention, joint and muscle aches and injection-site reactions [Review].

Small studies in children reported GHRP-2 as well tolerated; the longest followed six children for 18 to 24 months. Long-term safety of either peptide in healthy adults has not been studied. No established human dose exists outside approved labels.

How long do effects take in studies?

• GH peak: after an IV GHRP-2 test, GH peaked within 60 minutes in every subject. After oral GHRP-6, GH peaked at 60 to 75 minutes and returned to baseline by 150 to 180 minutes [Human].
• IGF-1: in critically ill adults, continuous GHRP-2 raised IGF-1 by 61% within 24 hours [Human RCT, n=26]; in older adults the rise appeared on day 1 and held through day 30 [Human, n=17].
• Growth in children: with intranasal GHRP-2, growth rate rose from 3.7 to 6.1 cm per year at 6 months [Human, uncontrolled, n=15].
• Stroke recovery: GHRP-6 with EGF was judged at 3 and 6 months, with no overall difference in disability [Human RCT, n=188].