Macimorelin
Also known as: Macrilen®
An oral ghrelin receptor agonist FDA-approved as a diagnostic test for adult growth hormone deficiency. Macimorelin (Macrilen®) is the only approved oral GH stimulation test. It acts as a selective agonist of the ghrelin receptor (GHSR-1a), stimulating growth hormone release from the anterior pituitary gland. Administered as a single oral dose in a clinical setting after overnight fasting, with blood samples collected at baseline and 30, 45, and 60 minutes post-administration to assess GH secretory capacity.
Research Status
Extensive Clinical Data
For research purposes only. Not approved for human use. Not medical advice.
Research Areas
Side Effects
Occurs in approximately 10-15% of patients. Usually transient and resolves without intervention. May be reduced by ensuring patient remains fasting and seated during test.
Reported in 1-5% of patients, typically related to fasting state. Patient should remain seated or recumbent during testing. Resolves after test completion.
Occurs in 1-3% of patients. May be related to fasting or stress of diagnostic procedure. Typically self-resolving.
Expected pharmacological effect of ghrelin receptor agonism. Patient should remain fasting during the diagnostic test period (approximately 1 hour).
Macimorelin may transiently elevate cortisol levels. Not clinically significant in single-dose diagnostic use. Relevant for patients with adrenal insufficiency — consult with endocrinologist.
Reported in <1% of patients. Transient and self-resolving.
Rare but documented. Patient should be monitored during test. Contraindicated in patients with uncontrolled cardiac arrhythmias or acute coronary syndrome.
Allergic reactions including rash, urticaria, or angioedema are rare but possible. Discontinue immediately and seek medical attention if signs of anaphylaxis develop.
Dosing Reference
| Parameter | Value |
|---|---|
| Dose range | 0.5 mg |
| Frequency | Single dose |
| Timing | Morning after overnight fast (minimum 8 hours), in clinical setting |
| Route | Oral |
Weight-based dosing: 0.5 mg/kg body weight. Maximum single dose typically 30 mg. Tablet dissolved in water immediately before administration. Blood samples collected at baseline and 30, 45, and 60 minutes post-administration. FDA-approved diagnostic agent (Macrilen®). For clinical diagnostic use only.
Research disclaimer
Figures drawn from published research literature and community logs. Not clinical recommendations. Consult a qualified professional. Research use only.
Reconstitution Guide
Do not use saline or bacteriostatic saline — use only bacteriostatic water for reconstitution
Do not shake the vial vigorously; gentle swirling prevents peptide degradation
Discard immediately if the solution appears cloudy, discolored, or contains visible particles
Use within 30 days of reconstitution when stored at 2–8°C
Do not freeze the reconstituted solution; freezing may denature the peptide
Use the PeptideVolt reconstitution calculator for your exact concentration
Molecular and Pharmacological Data
Macimorelin is a selective oral agonist of the ghrelin receptor (GHSR-1a) that stimulates growth hormone secretion from somatotroph cells in the anterior pituitary gland. By mimicking the action of endogenous ghrelin, macimorelin triggers GH release, allowing clinicians to assess the functional capacity of the GH axis in patients suspected of growth hormone deficiency. The magnitude of GH response to macimorelin administration serves as a diagnostic indicator of pituitary GH reserve.
Ghrelin Receptor (GHSR-1a) Activation
Macimorelin binds to and activates the growth hormone secretagogue receptor 1a on somatotroph cells, triggering intracellular signaling cascades that lead to GH synthesis and secretion
Hypothalamic-Pituitary-Somatotroph Axis
Activation of GHSR-1a stimulates GH-releasing hormone (GHRH) signaling and inhibits somatostatin, resulting in net stimulation of GH release from the anterior pituitary
GH Secretory Capacity Assessment
The GH response to macimorelin reflects the functional reserve of the somatotroph population and the integrity of the GH axis, enabling differentiation between GH-deficient and GH-sufficient individuals
- Macimorelin is the only FDA-approved oral GH stimulation test for diagnosing adult GH deficiency
- Selective GHSR-1a agonist with high specificity for growth hormone secretion
- Single oral dose eliminates need for IV administration or insulin-induced hypoglycemia stress testing
- GH response is measured at 30, 45, and 60 minutes post-administration to determine peak secretory capacity
- Diagnostic cutoff values have been established to differentiate GH-deficient from GH-sufficient adults
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