MK-677
An orally bioavailable ghrelin receptor agonist with genuine long-duration human RCT data, including a 2-year trial in older adults. Development was discontinued after efficacy endpoints were not met.
Growth Hormone
Macimorelin
The only orally active growth hormone secretagogue approved by the FDA, used as a single-dose diagnostic test for adult growth hormone deficiency.
Overview
Diagnosing growth hormone deficiency in adults used to require an insulin tolerance test — deliberately inducing hypoglycaemia under close supervision, which is unpleasant and risky. Macimorelin is swallowed as a solution and provokes a growth hormone response through the ghrelin receptor. If the pituitary can produce growth hormone, it does; if it cannot, the level stays low. That single reading gives the diagnosis.
An orally bioavailable pseudotripeptide GHS-R1a agonist. Stimulates pituitary GH release; a peak stimulated GH below the validated cut-off supports a diagnosis of adult growth hormone deficiency. Approval was based on a randomised, open-label, crossover trial demonstrating agreement with the insulin tolerance test, with sensitivity and specificity around 87% and 96% at the 2.8 ng/mL cut-off. It is a diagnostic agent only — there is no approved therapeutic indication and no completed programme for chronic use.
Research areas
GH deficiency diagnosisPituitary function testing
Dosing reported in the literature
Every protocol below is reproduced from a published study or approved labelling, with its source named. These are records of what was studied — not recommendations, and not a suggestion that any of them is appropriate for any person.
| Protocol as reported | Source |
|---|---|
| 0.5 mg/kg reconstituted as an oral solution after an overnight fast, with GH sampled at 30, 45, 60 and 90 minutes | Approved product labelling |
| Crossover comparison against the insulin tolerance test in adults with suspected GH deficiency | Garcia et al., Journal of Clinical Endocrinology & Metabolism 2018 |
Trial status
Pivotal diagnostic accuracy trial completed and published; approved 2017–2019.
Reported safety signals
- QT prolongation has been observed; concomitant QT-prolonging drugs should be stopped before testing.
- Dysgeusia, fatigue, headache, nausea and dizziness are the common transient effects.
- Recent use of growth hormone or drugs affecting the GH axis can invalidate the result.
- It is a diagnostic, not a therapy — repeated use has no established purpose or safety profile.
Common questions
Can macimorelin be used to raise growth hormone long term?
It has never been studied for that. It is approved as a single-dose diagnostic, and the QT signal in its labelling is a specific reason not to repeat-dose it casually.
Primary sources
Medical disclaimer
This page is for informational and research purposes only. Nothing here constitutes medical advice. The compounds discussed are research chemicals. Consult a qualified clinician before starting any protocol.
How this profile was built →