Macimorelin dosing & administration
FDA-approved diagnostic test for adult growth hormone deficiency
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Dosing
How much Macimorelin do I take?
Oral: Taken by mouth as a capsule, tablet, or liquid.
Bioavailability Varies by compound — many peptides are largely broken down in the gut, so little reaches the blood intact; some small molecules absorb well.
0.5 mg/kg
Frequency
Single dose
Duration
One-time diagnostic test
FDA-label (Macrilen) single oral dose for diagnosing adult growth hormone deficiency. Granules (60 mg) are reconstituted in 120 mL water (0.5 mg/mL) and taken after an 8-hour fast; serum GH below 2.8 ng/mL across the 30/45/60/90-minute draws confirms deficiency [4].
Timing
Best time to take
After fasting for at least 8 hours. [5]
With food?
Must be taken after at least an 8-hour fast: a liquid meal lowered peak levels by 55% and exposure by 49%. [5]
If stacking
This is a single-use diagnostic test, not a compound to be stacked. Blood GH is measured at 30, 45, 60 and 90 minutes after the dose. [5] Stop GH therapy at least one week before, and avoid drugs that affect GH release. [5]
Adjusting your dose
Increase if
- Initial test is inconclusive and retesting is clinically indicated
- Patient weight changes significantly between test administrations
- Clinical suspicion remains high despite initial negative result
Decrease if
- Not applicable — single fixed dose based on weight
- Dose is calculated once at 0.5 mg/kg body weight
Signs of right dose
- GH measured at all four draws (30, 45, 60 and 90 minutes) [5]
- Peak GH below 2.8 ng/mL confirms adult GH deficiency (a positive test); a higher peak is a negative test [5]
- Minimal side effects or patient tolerability issues
Administration
How do I use Macimorelin?
Reconstitution
What you need
Injection
Route
Not applicable — oral solution only
Best sites
Storage
Before reconstitution
Store in refrigerator at 2-8°C (36-46°F). Protect from light. Keep in original container until time of use.
After reconstitution
Once reconstituted in water, solution must be used within 30 minutes. Do not refrigerate after reconstitution. Discard any unused portion.
Signs of degradation — discard the vial
Sample daily schedule
Early morning (8-9 AM typical)
0.5 mg/kg body weight as a single dose (for example 35 mg for a 70 kg patient) [5] injection
Site: Oral administration
Fast for at least 8 hours. [5] Drink the dose within 30 seconds, then blood GH is measured at 30, 45, 60 and 90 minutes. [5] A peak GH below 2.8 ng/mL is a positive test (adult GH deficiency confirmed). [5]
Safety
Is Macimorelin safe?
Side effects
Commonly reported: Dysgeusia (abnormal taste), Dizziness, Headache, Fatigue, Nausea, Increased Appetite
Stop and seek help if
- Test has been completed and diagnostic results obtained (single-use diagnostic tool)
- Patient develops signs of QT prolongation or cardiac arrhythmias
- Patient experiences severe hypersensitivity reaction
- Contraindications emerge that preclude continued testing
- Physician determines additional testing is not clinically warranted
Macimorelin is a single-dose diagnostic test, not an ongoing therapy. Once administered and blood samples collected, the diagnostic protocol is complete. Additional testing requires a separate administration if clinically indicated by the healthcare provider.
Flagged pairings
- Other growth hormone secretagogues (ibutamoren, anamorelin, etc.) — Should not be combined during diagnostic testing as it will confound results
- GH replacement therapy — Stop GH therapy at least one week before testing; GH products can blunt the response to macimorelin [5]
- QT-prolonging drugs (quinidine, disopyramide, amiodarone, sotalol, dofetilide, antipsychotics, antiemetics) — Increases risk of QT prolongation and torsades de pointes. Avoid combination or use extreme caution with ECG monitoring.
- Strong CYP3A4 inducers (carbamazepine, phenytoin, rifampin, St. John's wort, modafinil) — Lower macimorelin levels and can cause a false positive result. Stop them and allow a washout before testing [5]
- Medications affecting electrolytes (diuretics, amphotericin B) — Electrolyte abnormalities increase QT prolongation risk. Ensure normal K+ and Mg+ before testing.
- Corticosteroids or opioids — May blunt GH response to macimorelin. Discontinue if possible before testing.
- Supplements affecting heart rhythm (stimulants with high caffeine) — Extreme caffeine intake before testing may increase arrhythmia risk. Recommend abstinence 24 hours before test.
Published research
What the studies show
Garcia JM, et al. · 2018
Macimorelin proved just as accurate as the dangerous insulin tolerance test for diagnosing growth hormone deficiency—catching real deficiencies 87% of the time and ruling out false positives 96% of the time. Plus, it's much safer and easier: just drink it instead of risking dangerous blood sugar drops from insulin shots.
Wang RL, et al. · 2025
Cryo-electron microscopy structures of the growth hormone secretagogue receptor (the ghrelin receptor) bound to macimorelin and anamorelin, showing how the two approved drugs bind and activate it.
Yuen KCJ, et al. · 2023
Review of growth hormone deficiency testing in children and adults: random GH levels are not recommended for screening, one or more stimulation tests may be needed, and peak GH cut-offs vary by age, test and assay.
Aeterna Zentaris · 2017
FDA label: single oral dose of 0.5 mg/kg after 8-hour fast (60 mg granules reconstituted in 120 mL water, 0.5 mg/mL); stimulated serum GH below 2.8 ng/mL confirms adult GH deficiency.
Aeterna Zentaris / U.S. Food and Drug Administration · 2026
Indicated for the diagnosis of adult GH deficiency; not established for BMI over 40 kg/m², and diagnostic accuracy was not demonstrated in a 102-patient pediatric study. Contraindications: none. Single oral dose of 0.5 mg/kg after at least an 8-hour fast; GH drawn at 30, 45, 60 and 90 minutes, and a peak below 2.8 ng/mL confirms AGHD. Warnings: QTc rises about 11 msec (avoid QT-prolonging drugs); strong CYP3A4 inducers can cause false positives; recent-onset hypothalamic disease can give false negatives. Stop GH therapy at least one week before testing. Against the ITT: 94% negative and 74% positive agreement. Most common reactions: dysgeusia 4.5%, dizziness, headache and fatigue 3.9% each, nausea and hunger 3.2%.
Head to head
Macimorelin compared
Want the full picture?
The complete Macimorelin research profile: mechanism of action, clinical studies, effectiveness timeline, and FAQ.