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approvedGrowth Hormone

Macimorelin

Also known as: Macrilen, AEZS-130, EP-01572

Macimorelin is an oral growth hormone secretagogue and ghrelin receptor agonist FDA-approved in 2017 as Macrilen for the diagnosis of adult growth hormone deficiency (AGHD). It is the first and only oral diagnostic test for GH deficiency, replacing the inconvenient and risky insulin tolerance test (ITT) as the clinical standard. A single oral dose stimulates GH release, with peak GH levels measured at 30, 45, 60, and 90 minutes post-ingestion to confirm or rule out GH deficiency.

4 cited references·5 researched benefits

Quick Answer

Macimorelin (Macrilen) is an oral ghrelin receptor agonist FDA-approved in 2017 as a diagnostic test for adult growth hormone deficiency. It replaced the insulin tolerance test as the preferred diagnostic method, offering a safer and simpler single-dose oral test. After ingestion, GH levels are measured at 30–90 minutes — a peak GH below 2.8 ng/mL confirms GH deficiency. It is not used as a therapeutic agent but solely as a diagnostic tool.

Key Facts

Mechanism
Macimorelin is a peptidomimetic agonist of the growth hormone secretagogue receptor type 1a (GHS-R1a), the ghrelin receptor. Upon oral absorption, it binds GHS-R1a on anterior pituitary somatotrophs, activating Gq-coupled phospholipase C signaling, increasing intracellular calcium, and triggering growth hormone release. In patients with intact pituitary function, this produces a robust GH response (typically >2.8 ng/mL). In patients with GH deficiency, the pituitary cannot respond adequately, resulting in blunted GH secretion that confirms the diagnosis. The compound is rapidly absorbed orally with peak plasma concentration at 30–75 minutes.
Research Status
approved
Half-Life
~4.1 hours
Primary Use
Growth Hormone
Table of Contents

Benefits

  • Accurate GH deficiency diagnosis — 92% concordance with insulin tolerance test, the prior gold standardstrong
  • Oral administration — eliminates the need for IV access and provocative testing with insulin or argininestrong
  • Superior safety — avoids the risk of severe hypoglycemia inherent to the insulin tolerance teststrong
  • Simple protocol — single oral dose with blood draws at 30, 45, 60, and 90 minutes in outpatient settingstrong
  • High reproducibility — test-retest reliability of 94% when repeated, exceeding other GH stimulation testsmoderate

Dosage Protocols

RouteDosage RangeFrequencyNotes
Oral solution0.5 mg/kg body weightSingle dose (diagnostic test)Dissolve granules in 120 mL water and consume within 30 minutes of preparation. Patient must fast overnight (≥8 hours). Blood samples drawn at baseline, 30, 45, 60, and 90 minutes post-dose. Peak GH <2.8 ng/mL confirms GH deficiency.

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Dysgeusia (taste disturbance) — metallic or bitter taste reported in 10–15% of patients during the testcommon
  • Headache — mild headache in approximately 5% of patientscommon
  • Nausea — mild gastrointestinal discomfort in 3–5% of patientscommon
  • Dizziness — transient lightheadedness reported rarelyrare
  • QTc prolongation — modest QTc increase observed; avoid in patients with pre-existing QT prolongation or concomitant QT-prolonging drugsrare

Frequently Asked Questions

How does the macimorelin diagnostic test work?
The test is performed in an outpatient clinical setting. The patient fasts overnight, then drinks a macimorelin solution (0.5 mg/kg). Blood samples are drawn at baseline, 30, 45, 60, and 90 minutes. Growth hormone levels are measured at each time point. If the maximum GH level at any time point is below 2.8 ng/mL, GH deficiency is confirmed. If peak GH exceeds 2.8 ng/mL, GH deficiency is excluded. The entire test takes about 2 hours.
Why was macimorelin developed to replace the insulin tolerance test?
The insulin tolerance test (ITT) was the prior gold standard for GH deficiency diagnosis but had major limitations: it requires IV insulin injection to induce hypoglycemia (blood glucose <40 mg/dL), carries risk of seizures and loss of consciousness, is contraindicated in patients with cardiovascular disease or epilepsy, requires continuous medical supervision, and is poorly tolerated. Macimorelin provides equivalent diagnostic accuracy with a simple oral dose and no hypoglycemia risk.
Can macimorelin be used therapeutically to increase growth hormone?
Macimorelin is FDA-approved only as a diagnostic agent, not a therapeutic. While it does stimulate GH release, its pharmacokinetic profile (single-dose, short-acting) is designed for diagnostic testing rather than sustained GH augmentation. For therapeutic GH stimulation, other secretagogues with better pharmacokinetic profiles (e.g., daily or continuous-release formulations) would be more appropriate. No therapeutic trials have been conducted with macimorelin.
How much does the macimorelin test cost compared to other GH stimulation tests?
The macimorelin test costs approximately $1,500–$3,000 for the drug plus laboratory fees. The insulin tolerance test is less expensive for the provocative agent (insulin is cheap) but requires intensive medical supervision, IV access, and monitoring — often making the total cost comparable. Arginine + GHRH testing costs vary. Most endocrinologists consider macimorelin cost-effective given its safety and convenience advantages.
Are there limitations to the macimorelin test?
Key limitations include: (1) BMI effect — obese patients may have blunted GH response leading to false positives; BMI-adjusted cutoffs are being studied. (2) Drug interactions — drugs that prolong QTc or inhibit CYP3A4 can affect results. (3) Age considerations — GH response naturally declines with age, potentially requiring age-adjusted cutpoints. (4) Limited pediatric data — the test is approved for adults only. (5) Cost — macimorelin is more expensive than insulin as a provocative agent.

References

  1. 1
    Macimorelin as a diagnostic test for adult GH deficiency: phase 3 pivotal trial(2018)PubMed ↗
  2. 2
    Oral macimorelin versus injectable growth hormone stimulation tests for diagnosis of adult GH deficiency(2018)PubMed ↗
  3. 3
    FDA approval of macimorelin: a new era in GH deficiency diagnosis(2018)PubMed ↗
  4. 4
    Growth hormone secretagogues: history, mechanism of action, and clinical development(1999)PubMed ↗

Latest Research

Last updated: 2026-02-19