Growth hormone axis
Hexarelin vs Ipamorelin: Research Comparison
Hexarelin and ipamorelin are synthetic peptides that act on the ghrelin receptor and trigger growth hormone release. Hexarelin also binds CD36, a receptor on heart muscle and blood vessel cells. Ipamorelin was more selective for growth hormone in pig studies.
Side-by-side comparison
| Attribute | Hexarelin | Ipamorelin |
|---|---|---|
| What it is | Six-amino-acid GHRP, a stable analogue of GHRP-6 | Five-amino-acid peptide from Novo Nordisk |
| Receptors | Ghrelin receptor and CD36 | Ghrelin receptor |
| Other hormones | Raised prolactin and cortisol in healthy men | Did not raise ACTH or cortisol in pigs; human data limited |
| Repeated use in people | Growth hormone response partly weakened over 16 weeks and recovered after stopping | No long-term human data |
| Human data | Small placebo-controlled studies in healthy men and older adults | Pharmacokinetic study in healthy men; phase 2 trial after bowel surgery found no clear difference from placebo |
Detailed analysis
Hexarelin (examorelin) was made in Milan in the early 1990s as a more chemically stable analogue of GHRP-6 (Deghenghi et al., 1994). Besides the ghrelin receptor, it binds CD36 (Bodart et al., 2002); in perfused rodent hearts it raised coronary perfusion pressure, and this response was missing in hearts lacking CD36. In small placebo-controlled studies in healthy men it raised growth hormone along with prolactin and cortisol. In 12 healthy older adults given hexarelin for 16 weeks, the growth hormone response partly weakened and recovered after stopping, and IGF-1, body composition and bone density did not change (Rahim et al., 1998).
Ipamorelin (NNC 26-0161) released growth hormone in pigs without raising ACTH or cortisol (Raun et al., 1998). In healthy men its half-life was about two hours (Gobburu et al., 1999). A phase 2 placebo-controlled trial in 114 adults after bowel surgery found no clear difference from placebo (Beck et al., 2014).
Both have only small or short human studies and no long-term safety data.
Key differences
- ·Hexarelin binds both the ghrelin receptor and CD36; ipamorelin binds the ghrelin receptor.
- ·Hexarelin raised prolactin and cortisol in healthy men; ipamorelin did not raise ACTH or cortisol in pigs.
- ·Hexarelin's growth hormone response partly weakened over 16 weeks in older adults.
- ·Neither is a licensed medicine.
Research summary
Hexarelin evidence comes from rat and rodent heart studies (Bodart et al., 2002) and small human studies (Rahim et al., 1998). Ipamorelin evidence comes from pig and rat studies (Raun et al., 1998) and two human studies. Neither has large controlled trials or long-term safety data. Supplied for laboratory research use only.