Macimorelin Evidence Guide
Macimorelin (Macrilen) is FDA-approved as the first oral diagnostic test for adult GH deficiency, replacing the insulin tolerance test in many clinical settings. Its role is diagnostic, not therapeutic. For researchers studying the GH/IGF-1 axis and needing a validated, reproducible stimulation test, macimorelin is the current standard of care with actual FDA approval behind it.
Our Take
Macimorelin (Macrilen) is FDA-approved as the first oral diagnostic test for adult GH deficiency, replacing the insulin tolerance test in many clinical settings. Its role is diagnostic, not therapeutic. For researchers studying the GH/IGF-1 axis and needing a validated, reproducible stimulation test, macimorelin is the current standard of care with actual FDA approval behind it.
- Best for
- Adult GH deficiency diagnosis, GH stimulation testing, GH axis research
- Evidence grade
- Level A
- Confidence
- High
- Starting point
- 0.5mg/kg oral single dose (diagnostic use only)
Benefits and Evidence
- GH Deficiency Diagnosis: Level A, includes human evidence - Validated diagnostic test with 87% sensitivity and 96% specificity for AGHD using a 2.8 ng/mL cutoff, comparable to the insulin tolerance test with improved safety and reproducibility.
- Acute GH Release: Level A, includes human evidence - Reliable, dose-dependent GH release peaking at 30-90 minutes after oral administration in healthy adults, with consistent and reproducible responses on repeat testing.
Side Effects and Warnings
- Dysgeusia (taste disturbance)
- Dizziness
- Headache
- Nausea
- Fatigue
- Hunger
- Approved only as a single-dose diagnostic agent - not for chronic GH stimulation
- False positive results possible in patients on strong CYP3A4 inducers
Research Dosage References
- <strong>Oral</strong> - 0.5 mg/kg - Single dose (diagnostic) - FDA-approved as a single-dose diagnostic test. Dissolve in water and drink within 30 minutes. Blood samples for GH at 30, 45, 60, and 90 minutes post-dose.
Mechanism of Action
Macimorelin is a synthetic peptidomimetic that acts as an agonist at the growth hormone secretagogue receptor type 1a (GHSR1a), the endogenous receptor for ghrelin. Upon oral administration, it is absorbed from the gastrointestinal tract and reaches the pituitary gland, where GHSR1a activation on somatotroph cells triggers growth hormone release. The GH-releasing effect of macimorelin is dose-dependent and robust in individuals with intact GH secretory capacity, but attenuated or absent in patients with true growth hormone deficiency. This difference in GH response magnitude forms the basis of its diagnostic utility - a peak GH level below a defined cutoff (2.8 ng/mL) after macimorelin administration is indicative of AGHD. As a ghrelin mimetic, macimorelin also has appetite-stimulating properties, though these are transient given the single-dose diagnostic application. Unlike MK-677 (another oral ghrelin mimetic), macimorelin is not intended for chronic administration.
Legal Status
FDA approved (2017, Macrilen). Prescription required. Not a controlled substance. Indicated only for diagnostic use.
Primary Sources
- Oral macimorelin diagnostic test for adult GH deficiency: validation study. Journal of Clinical Endocrinology & Metabolism, 2018.
- Macimorelin as a diagnostic test for adult growth hormone deficiency: Phase 3 results. Journal of Clinical Endocrinology & Metabolism, 2017.