MK-677 (Ibutamoren)
What MK-677 is
MK-677, also called ibutamoren, is a growth hormone secretagogue. It is not a peptide, and that distinction is the most useful thing to understand about it. Where ipamorelin, sermorelin and CJC-1295 are chains of amino acids that must be injected, MK-677 is a small non-peptide molecule that survives the digestive tract and is taken orally.
It acts as an agonist at the ghrelin receptor, the same receptor ipamorelin works through. The mechanism is shared; the delivery is not.
Why oral matters
Peptides are broken down by digestive enzymes, which is why almost everything else in this reference is injected. MK-677 is orally bioavailable because its structure is not a peptide bond chain for those enzymes to cleave.
The second consequence is duration. Published pharmacokinetics give MK-677 a half-life of around 24 hours, which supports once-daily dosing in study protocols. Compare that with ipamorelin at roughly two hours or sermorelin at ten to twenty minutes, and the practical difference is a sustained elevation rather than a pulse.
At a glance
| Class | Non-peptide growth hormone secretagogue |
|---|---|
| Target | Ghrelin receptor (GHSR) |
| Presentation | Capsule or oral solution |
| Reported half-life | Approximately 24 hours |
| Reconstitution | None required |
| Storage | Room temperature, dry, away from light |
Compared with the injectable secretagogues
| MK-677 | Ipamorelin | Sermorelin | |
|---|---|---|---|
| Type | Small molecule | Peptide | Peptide |
| Route | Oral | Injection | Injection |
| Receptor | Ghrelin | Ghrelin | GHRH |
| Half-life | ~24 hours | ~2 hours | ~10-20 minutes |
| Reconstitution | None | Required | Required |
| Storage | Room temp | Refrigerated | Refrigerated |
Ipamorelin and MK-677 share a receptor. Sermorelin works through a different one, GHRH, which is why the two mechanisms are sometimes studied in combination rather than as alternatives.
Handling
There is no reconstitution step, no diluent to choose and no concentration calculation. That removes the three most common sources of error covered elsewhere on this site.
Store at room temperature in a dry place away from light. Unlike lyophilised peptides, MK-677 does not require refrigeration, and a capsule or oral solution left in a fridge risks condensation without any stability benefit.
Where MK-677 is supplied as an oral solution rather than capsules, check the stated concentration on the label. Solutions vary between suppliers and the figure does not carry across.
Frequently asked
Is MK-677 a SARM? No, though it is frequently sold and discussed alongside them. SARMs are selective androgen receptor modulators. MK-677 does not act at the androgen receptor at all; it works through the ghrelin receptor.
Is it a peptide? No. It is a non-peptide small molecule, which is precisely why it can be taken orally when the peptide secretagogues cannot.
Does it need refrigerating? No. Room temperature, dry, out of light.
Is it the same as HGH? No. Growth hormone itself is a protein administered directly. A secretagogue acts on the body's own release mechanism instead, which is a different approach with a different profile.