A 6-amino-acid synthetic peptide that stimulates growth hormone release by activating the ghrelin receptor (GHS-R1a). One of the first GH secretagogues developed. Notable for its strong appetite-stimulating effects and robust GH release, but less selective than ipamorelin.
GHRP-6 (His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) is a synthetic hexapeptide and one of the earliest growth hormone releasing peptides developed. It acts as a potent agonist at the ghrelin receptor (GHS-R1a), triggering robust GH release from the anterior pituitary.
Unlike the more selective ipamorelin, GHRP-6 also significantly stimulates appetite (via ghrelin pathway activation), increases cortisol and prolactin levels, and can cause intense hunger within 20 minutes of injection. This makes it less 'clean' than ipamorelin but potentially more effective for individuals who need appetite stimulation (e.g., recovering from illness or wasting conditions).
GHRP-6 (Growth Hormone-Releasing Peptide-6) was one of the first synthetic GH secretagogues developed, originally synthesized by Cyril Bowers in the 1980s. It is a hexapeptide (6 amino acids: His-D-Trp-Ala-Trp-D-Phe-Lys-NH2) that powerfully stimulates GH release by activating the ghrelin receptor (GHS-R1a) on pituitary somatotrophs. However, GHRP-6 is the least selective of the major GH secretagogues — it significantly stimulates appetite (via ghrelin pathway activation), elevates cortisol, and increases prolactin levels alongside its GH-releasing effect.
Because of these off-target effects, GHRP-6 has been largely superseded by more selective alternatives like ipamorelin and GHRP-2 in clinical practice. Its primary remaining use is in situations where appetite stimulation is a desired effect (e.g., recovery from illness, underweight patients) or in research settings studying ghrelin-receptor pharmacology. It remains an important compound historically as the peptide that proved the concept of synthetic GH secretagogues.
GHRP-6 is a non-selective GHS-R1a agonist that activates multiple downstream pathways. In addition to GH release from somatotrophs, it activates hypothalamic appetite circuits (mimicking ghrelin's orexigenic effect) and stimulates the HPA axis, increasing both cortisol and prolactin. This broad activation profile is why it has been largely replaced by ipamorelin for clinical use.
| Pathway | Effect | Significance |
|---|---|---|
| GH release | GHS-R1a activation on pituitary somatotrophs | Robust GH increase (greater magnitude than ipamorelin) |
| Appetite stimulation | Ghrelin-like activation of NPY/AgRP neurons in arcuate nucleus | Intense hunger within 20 min — useful for wasting, problematic for weight management |
| Cortisol increase | HPA axis stimulation via hypothalamic CRH release | Undesirable side effect not seen with ipamorelin |
| Prolactin increase | Pituitary lactotroph stimulation | Undesirable; can cause gynecomastia with chronic use |
| Gastric motility | Increases gastric emptying and GI motility | May benefit gastroparesis but can cause GI discomfort |
| Study | Design | Findings | Level |
|---|---|---|---|
| GH release | Phase I/II human studies | Dose-dependent GH increase peaking at 15-30 min post-injection. Greater magnitude than GHRP-2 or ipamorelin. | Level II |
| Appetite stimulation | Clinical observation | Significant hunger increase reported by virtually all subjects. Onset ~20 min, duration 1-2 hours. | Level II-III |
| Cardiac protection | Preclinical | GHRP-6 showed cardioprotective effects in ischemia-reperfusion models independent of GH release | Preclinical |
| Comparison to ipamorelin | Clinical studies | GHRP-6 produces greater GH release but with cortisol, prolactin, and appetite side effects that ipamorelin avoids | Level II |
Intense appetite stimulation: GHRP-6 produces the strongest appetite-stimulating effect of any GH secretagogue — users consistently report significant hunger within 20-30 minutes of injection. This is a direct consequence of potent ghrelin-receptor activation and limits its utility for patients managing body weight.
Cortisol elevation: GHRP-6 causes meaningful acute cortisol increases, which is undesirable for long-term use. Chronic cortisol elevation can impair immune function, promote abdominal fat storage, and disrupt sleep.
Prolactin elevation: Prolactin increases are more pronounced than with GHRP-2 or ipamorelin. Chronically elevated prolactin can affect reproductive function and mood.
GH-related effects: Water retention, joint stiffness, and parasthesias (numbness/tingling) at higher doses, consistent with the GH secretagogue class.
| Jurisdiction | Status |
|---|---|
| FDA | Not approved. |
| WADA | Banned under S2 (peptide hormones and growth factors) |
| Status | Largely superseded by ipamorelin in clinical use due to selectivity issues |
| Feature | GHRP-6 | Ipamorelin |
|---|---|---|
| GH release | Strong (higher peak) | Moderate (lower peak but cleaner) |
| Appetite effect | Intense hunger | Minimal |
| Cortisol | Increases significantly | No significant change |
| Prolactin | Increases | No significant change |
| Selectivity | Low (multiple off-target effects) | High (GH-selective) |
| Clinical preference | Wasting conditions, appetite loss | Anti-aging, body composition, general GH optimization |