The first synthetic growth hormone-releasing peptide. Triggers a short GH pulse in humans; never approved as a drug anywhere.
Also called Growth hormone-releasing peptide-6, Growth hormone-releasing hexapeptide, [His1,Lys6]-GHRP, SK&F 110679
GHRP-6 is a six-amino-acid peptide that Cyril Bowers and Frank Momany designed in the early 1980s, years before anyone knew the receptor it hit. Given into a vein, it makes the pituitary release a burst of growth hormone; in an early human study, GH peaked about 45 minutes after a 30-minute infusion began and was back to baseline by about 3.5 hours. In 1996 Merck scientists cloned the receptor it acts on, and in 1999 Japanese researchers found the body's own hormone for that receptor, ghrelin. So GHRP-6 is best understood as a crude, short-acting ghrelin mimic.
What has been shown in people is narrow: single injections raise growth hormone, also raise cortisol, ACTH and prolactin at higher doses, and act together with GHRH to give a much larger GH peak than either alone. That last effect made GHRH plus GHRP-6 a diagnostic test for growth hormone deficiency in some European centers. No published human trial has tested GHRP-6 for muscle gain, fat loss, injury healing or anything else people take it for.
The healing and organ-protection claims come from Cuban and other animal studies in which GHRP-6 reduced damage to heart, liver and gut tissue, partly through a second receptor called CD36. Those results have not been repeated in human trials. GHRP-6 is banned in sport by WADA and the FDA has flagged it as a safety concern for outsourcing-facility compounding.
What it binds to, and what happens inside the body after that, step by step.
GHRP-6 binds the growth hormone secretagogue receptor (GHS-R1a), the same receptor ghrelin uses, on pituitary somatotroph cells and in the hypothalamus. It works through a different pathway from GHRH, which is why the two together release far more GH than either one alone. It also binds CD36, a scavenger receptor found in heart muscle and blood vessels, which is the proposed route for the tissue-protection effects seen in animals.
Human results and animal results are kept apart below. A result in rats tells you a mechanism is plausible. It does not tell you what happens in a person.
Human evidence is limited to small, mostly single-dose studies in healthy volunteers and patients being tested for GH deficiency: GHRP-6 reliably causes a GH pulse, raises cortisol and prolactin at higher doses, and stacks with GHRH for diagnosis. There are no human trials of GHRP-6 for body composition, strength, recovery or healing. The cytoprotective and antifibrotic effects are animal and cell findings only.
18 healthy men, single IV doses vs placebo
Peak GH rose from 1.2 on placebo to 68.7 micrograms/L at 1 microgram/kg; cortisol and prolactin roughly doubled at that dose, and low doses combined with GHRH acted synergistically.
Read the study17 healthy men given 30-minute IV infusions of 0.05 to 2.5 micrograms/kg; 8 also received saline
GH rose consistently from 0.25 micrograms/kg, peaking at 63.0 micrograms/L at 1.0 microgram/kg; GH peaked at 45 minutes and was back to baseline by 210 minutes, with no change in ACTH, LH, FSH or TSH.
Read the studyHealthy men, placebo-controlled (randomization not reported), 4 x 50 microgram IV boluses during the night
Night-time GH rose (15.4 vs 5.5 ng/mL), ACTH rose modestly (21.0 vs 16.6 pg/mL) and cortisol more than doubled (56.0 vs 25.2 ng/mL); stage 2 sleep increased while deep slow-wave sleep did not change.
Read the studyHealthy young men, placebo-controlled (randomization not reported); oral, intranasal and sublingual GHRP-6
Oral GHRP-6 at 300 micrograms/kg did not change GH; intranasal 30 micrograms/kg raised GH across the night, so route and dose decide whether it does anything.
Read the study9 healthy men, single IV bolus of 100, 200 or 400 micrograms/kg (Cuba)
Distribution half-life was 7.6 minutes and elimination half-life about 2.5 hours; exposure rose roughly in proportion to dose.
Read the study83 adults at least one year after traumatic brain injury
With GHRH 1 microgram/kg plus GHRP-6 1 microgram/kg IV, the 30-minute GH value correlated with the peak at r = 0.972, so one blood draw classified 78 of 83 patients the same way.
Read the studyRat pituitary cells; rats, monkeys, lambs, calves
The hexapeptide released GH within 2 minutes of IV injection in rats, worked across species, and increased weight gain in immature rats dosed for 9 to 25 days.
Read the studyThese are questions the published research has not answered.
No product containing GHRP-6 is approved as a medicine by the FDA.
No regulator has approved GHRP-6 for any use. It is sold online as a research chemical, which means no one checks identity, purity or sterility. WADA lists GHRP-6 by name under S2.2.4 (GH-releasing peptides), prohibited at all times.
How much of GHRP-6 is left after a single dose
Simple first-order model from the published half-life. Real clearance varies with dose, route, kidney and liver function and formulation. This is not a dosing schedule.
This table records the doses that trials and approved labels used, with the source for each row. It is a record of research, not a recommendation, and it is open to free members.
Which symptoms are expected and which mean stop and get help: side effects and red flags.
Tap a claim to see what the studies found.
It raises GH for a short window. No human study has measured muscle or strength after a course of GHRP-6, and short GH pulses are not the same exposure as daily GH injections.
The protective effects come from animal models of heart attack, liver injury and gut damage. There are no human healing trials.
Hunger is the expected effect of a ghrelin mimic and is proven for GHRP-2 in humans, but controlled human data specific to GHRP-6 appetite are thin.
In the one placebo-controlled sleep-lab study, GHRP-6 increased light stage 2 sleep, left slow-wave sleep unchanged, and raised night-time cortisol.
At 1 microgram/kg IV it roughly doubled cortisol and prolactin in healthy men, and repeated night-time doses raised ACTH and cortisol. The 1984 animal claim of GH specificity did not fully hold in humans.
These pairings come up often. Almost none have been tested together in a trial, and the evidence note on each says so plainly.
GHRH and ghrelin-receptor agonists act on different pathways, so together they release more GH than either alone.
EvidenceThe synergy is shown for single IV doses of GHRP-6 with native GHRH in healthy men (Bowers 1990). No trial has tested this combination with CJC-1295 or measured any outcome beyond acute GH levels.
No published stability data for research-grade GHRP-6. Lyophilized peptides of this kind are generally kept sealed, dry, cold and away from light.
No published in-use stability data for GHRP-6 solutions. Reconstituted peptides are generally refrigerated and used within a short window; sterility depends entirely on the product and technique.
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