What it is
GHRP-6 is a synthetic six amino acid peptide, His-D-Trp-Ala-Trp-D-Phe-Lys-NH2, that makes the pituitary release growth hormone. Cyril Bowers and colleagues described it in 1984 as a hexapeptide that acts on the pituitary to release GH specifically. It is the parent compound of the GHRP family, which later produced GHRP-2, hexarelin and, in a different chemical direction, ipamorelin and the oral MK-677.
It has never been approved as a medicine anywhere we could find. In the research literature it has had a second life in Cuba, where a group has studied it for tissue protection after heart attack and stroke.
How it works
GHRP-6 binds the growth hormone secretagogue receptor (GHS-R1a). For years the receptor it acted on had no known natural partner. In 1999 Kojima and colleagues identified ghrelin, a peptide made mainly in the stomach, as its natural ligand. GHRP-6 is therefore a small synthetic ghrelin mimic, which explains why it raises GH and also drives appetite.
Two points from the early human work matter:
- It adds to GHRH rather than replacing it. Bowers' 1990 study found that low doses of GHRP-6 combined with GHRH gave a larger GH release than either alone. The two compounds act on different receptors and pathways.
- It is not perfectly selective. At the highest dose tested, prolactin and cortisol roughly doubled above baseline, while LH and TSH did not change in the first hour.
What the research found
Human studies
- GH release in healthy men (Bowers 1990). Eighteen men received single intravenous doses of 0.1, 0.3 and 1.0 mcg/kg. Peak GH rose steeply with dose, and submaximal doses combined with GHRH produced a synergistic response.
- Pharmacokinetics (Cabrales 2013). A Cuban group characterised how GHRP-6 is handled by the body in nine healthy male volunteers. A companion dose-escalation study reported intravenous GHRP-6 to be safe in healthy volunteers.
- Stroke (Hernandez-Bernal 2024). In a phase I/II open-label trial, 36 patients with acute ischaemic stroke were randomised to one of two doses of EGF plus GHRP-6, given intravenously twice daily for seven days, or to standard care. The primary aim was safety. Serious adverse events were within the trial's pre-set limit, and the authors reported better neurological recovery in the treated groups. The trial was small and unblinded, and because GHRP-6 was always given with EGF, it cannot tell you what GHRP-6 does on its own.
Animal studies
The Cuban group's 2017 review summarises a long line of animal work. In a pig model of heart attack, GHRP-6 reduced the amount of heart muscle lost. In rat models of ischaemia and reperfusion it reduced damage to the liver, lungs, gut and kidneys, and combined with EGF it showed benefit in animal models of brain ischaemia. These are the findings behind the stroke trial. They have not been reproduced in large human trials.
Side effects reported in studies
In the 1990 study, the only adverse effect noted was brief facial flushing, which occurred in subjects receiving GHRH rather than GHRP-6. Rises in prolactin and cortisol were seen at the top dose. Hunger is the class effect people associate with GHRP-6, which follows from its action on the ghrelin receptor. The stroke trial reported mostly mild to moderate events such as fever, tremor, nausea, vomiting, sweating and shivering, in very ill patients who were also receiving EGF. As with any compound that raises GH and IGF-1, the theoretical long-term concerns mirror those of growth hormone: fluid retention, joint aches, reduced insulin sensitivity and the open question of IGF-1 and cancer.
GHRP-6 vs GHRP-2
| GHRP-6 | GHRP-2 | |
|---|---|---|
| Sequence | His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 | D-Ala-D-2Nal-Ala-Trp-D-Phe-Lys-NH2 |
| Receptor | Ghrelin receptor | Ghrelin receptor |
| Regulatory footprint | None | Diagnostic agent in Japan |
| Best human data | Acute GH tests, Cuban phase I and stroke trials | Diagnostic validation, paediatric trials |
For how GHRPs compare with GHRH analogues such as sermorelin and CJC-1295, see the sermorelin page.
Status in the Philippines
No GHRP-6 product is registered with FDA Philippines, so it cannot be sold locally as a medicine. It is available through research-chemical suppliers. Athletes should treat it as off limits: the WADA Prohibited List names GHRP-6 under section S2, prohibited in and out of competition.
Storage
Keep lyophilised vials refrigerated, especially through Philippine summers and brownouts when a room can sit well above 30°C. Once mixed with bacteriostatic water, store at 2 to 8°C and away from the freezer compartment. The reconstitution calculator handles the mixing arithmetic.
