Ipamorelin vs MK-677: selective peptide vs oral small molecule, same receptor
Both activate the ghrelin receptor to stimulate growth hormone release. One's a peptide injection, the other's a daily pill. The trade-offs are bigger than the mechanism difference suggests.
Ipamorelin and MK-677 both target the growth hormone secretagogue receptor (GHSR-1a) to stimulate GH release. Ipamorelin is a synthetic pentapeptide — injection-delivered, short-duration. MK-677 (ibutamoren) is an orally bioavailable small molecule with a longer half-life that supports once-daily dosing. Neither is FDA approved. Both are on the FDA's Category 2 list.
| Field | Ipamorelin | MK-677 (ibutamoren) |
|---|---|---|
| Brand names | Nutrobal | |
| Manufacturer | Research vendors | Research vendors |
| FDA approved | Not FDA approved; Category 2 (Sep 2023) | Not FDA approved; Category 2 (Sep 2023) |
| Indication | Research: GH axis stimulation | Research: GH axis stimulation (oral) |
| Mechanism | Selective GHSR-1a agonist (peptide) | GHSR-1a agonist (small molecule, oral) |
| Delivery | Subcutaneous injection (daily or split) | Oral daily tablet |
Primary sources
- MK-677 (ibutamoren): MK-677 in elderly adults (Annals of Internal Medicine, 2008)
Frequently asked
Do they produce different amounts of GH release?
MK-677 produces sustained daily GH elevation while preserving some pulsatility. Ipamorelin produces more episodic pulses matching its short half-life. Total 24-hour GH/IGF-1 exposure is typically higher with MK-677 at biohacker-typical doses.
Which has more side effects?
MK-677 reliably increases appetite (ghrelin mimicry at the same receptor), which biohackers pursuing body composition usually don't want. Ipamorelin is more selective and doesn't have the same appetite-stimulating effect. Both share the theoretical cancer-risk concerns of sustained IGF-1 elevation.
Can I stack them?
Biohacker protocols don't commonly stack them since they hit the same receptor. A more common stack is either drug paired with a GHRH analog (CJC-1295) which hits a different pathway.