Macimorelin
Orally active ghrelin-receptor (GHSR) agonist approved as a single-dose diagnostic test for adult growth hormone deficiency. It provokes a transient GH surge; peak GH below a threshold confirms deficiency.
01 Overview
Macimorelin (brand Macrilen) is a small peptidomimetic that stimulates the growth hormone secretagogue receptor, triggering pituitary GH release. Unlike injectable provocative agents, it is taken as a single oral solution, making the adult GHD stimulation test simpler than the historical insulin tolerance test.
It is a diagnostic agent, not a therapy — it is dosed once, and its role is to measure the pituitary's capacity to release GH rather than to raise IGF-1 chronically. It was FDA-approved in 2017 following head-to-head validation against the insulin tolerance test.
02 Mechanism
Agonist at the ghrelin/growth hormone secretagogue receptor (GHSR-1a) on pituitary somatotrophs, evoking a transient pulse of endogenous GH.
03 Dosing
| Tier | Dose | Route | Notes |
|---|---|---|---|
| Diagnostic dose | 0.5 mg/kg | Oral | Single oral solution after overnight fast; GH sampled at 30, 45, 60, 90 min. |
04 Effects
| Effect | Magnitude | Evidence | |
|---|---|---|---|
| Provokes GH surgeReliably stimulates a measurable pituitary GH pulse, allowing diagnosis of adult GHD. | peak GH used at 2.8 ng/mL cutoff | Clinical | |
| Distinguishes GH-deficient patientsComparable diagnostic accuracy to the insulin tolerance test without hypoglycaemia risk. | ~87% sensitivity/96% specificity vs ITT | Clinical |
05 Side effects
| Effect | Severity | Frequency | Evidence | Countermeasures |
|---|---|---|---|---|
| DysgeusiaTransient bitter or metallic taste after ingestion. | Mild | Common | Clinical | |
| QT prolongationModest QTc prolongation observed; caution with other QT-prolonging drugs. | Moderate | Uncommon | Clinical |