Macimorelin
Macimorelin (Macrilen) is an extraordinary, FDA-approved, orally bioavailable ghrelin receptor agonist. Originally developed strictly as a clinical diagnostic tool to identify severe Adult Growth Hormone Deficiency (AGHD), its uniquely high resistance to gastric destruction has thrust it into the spotlight of advanced oral biohacking. Unlike standard GHRPs that demand subcutaneous injection, a single oral dose of Macimorelin can reliably force a massive, clinically measurable spike in endogenous Growth Hormone within 60 minutes, offering elite restorative benefits without the needle.
Quick Stats
Scientific Data
Mechanism of Action
Macimorelin (AEZS-130) is a peptidomimetic ghrelin receptor agonist — an orally active synthetic compound that mimics ghrelin binding at GHS-R1a on pituitary somatotroph cells. Unlike ghrelin itself (28 amino acids, SubQ only), macimorelin is orally bioavailable with ~90% GHS-R1a receptor selectivity.
Macimorelin is FDA-approved (Macrilen) specifically for diagnosis of adult growth hormone deficiency (AGHD). A single oral dose (0.5 mg/kg) reliably stimulates a GH peak, providing a safe, patient-friendly alternative to the insulin tolerance test (ITT) or arginine stimulation test. Off-label, it is being explored for recovery of GH axis function, though its primary use is diagnostic.
Source: FDA Label (Macrilen), PMID: 30011461
Background & History
Macimorelin (AEZS-130) is an orally active peptidomimetic ghrelin agonist developed by Aeterna Zentaris, FDA-approved in 2017 as Macrilen for the diagnosis of adult growth hormone deficiency (AGHD). It is the only oral GH stimulation test approved in the US, replacing older tests (insulin tolerance test, arginine + GHRH) that required IV administration and medical supervision for hypoglycemia risk. In biohacking circles, macimorelin's oral activity and ghrelin receptor selectivity (similar to MK-677 but with different pharmacokinetics) have attracted interest as an alternative or complement to MK-677 for GH optimization. One key difference: macimorelin has a ~4-6 hour half-life vs MK-677's 5-hour half-life, but MK-677 causes sustained IGF-1 elevation for 24 hours while macimorelin causes a discrete diagnostic peak.
Research Use Cases
- ✓Adult growth hormone deficiency diagnosis (FDA-approved, Macrilen)
- ✓GH secretagogue research: oral GH pulse stimulation
- ✓Assessment of pituitary GH reserve without IV procedures
- ✓Biohacking GH optimization as injection-free alternative to GHRP stack
Dosing Protocol
| Typical Dose | 0.5 mg/kg (diagnostic) or 1-2 mg/day (research) |
| Frequency | 1× daily (oral) |
| Half-Life | ~4-6 hours |
Dosing Protocols
Diagnostic (FDA-approved)
Body-Weight Dosing Reference
Estimated doses extrapolated from the published research range of 500–2000 mcg/day (referenced to 70 kg / 154 lb). These are approximations — consult a qualified healthcare provider for personalised guidance.
| Weight | Low Dose | Target Dose | High Dose |
|---|---|---|---|
| 120 lb(54 kg) | 386 mcg | 964 mcg | 1543 mcg |
| 140 lb(63 kg) | 450 mcg | 1125 mcg | 1800 mcg |
| 160 lb(73 kg) | 521 mcg | 1304 mcg | 2086 mcg |
| 180 lb(82 kg) | 586 mcg | 1464 mcg | 2343 mcg |
| 200 lb(91 kg) | 650 mcg | 1625 mcg | 2600 mcg |
| 220 lb(100 kg) | 714 mcg | 1786 mcg | 2857 mcg |
| 250 lb(113 kg) | 807 mcg | 2018 mcg | 3229 mcg |
💉 For exact syringe units based on your vial concentration, use the Macimorelin Reconstitution Calculator →
Administration
Expected Timeline
Who Is It For?
GHD Diagnosis
HighFDA-approved diagnostic agent. Replaces invasive insulin tolerance test. Single oral dose protocol.
Safety & Considerations
FDA-approved (Macrilen). Single-dose diagnostic use. Well-tolerated. May cause dizziness, nausea, or hunger (ghrelin effects). Not for therapeutic use in current approved form.
Regulatory & Legal Status
FDA-approved as Macrilen® for diagnosis of adult growth hormone deficiency
Competitive athletes subject to anti-doping controls should not use Macimorelin.
Prescription Drug
US Compounding: Not eligible / not available
⚠️ This information is for educational purposes only and may not reflect the most current regulatory updates. Always verify with official FDA, WADA, and jurisdiction-specific sources before use.
Interactions & Contraindications
Contains lactose — avoid in lactose intolerance. Moderate CYP3A4 inhibitors increase macimorelin exposure — avoid ketoconazole, erythromycin, grapefruit juice within 2 hours. Must fast for 8 hours before the diagnostic dose. Fatty meal blunts GH peak by 50%. Somatostatin analogs (octreotide) antagonize the GH response. Clonidine and other GH-stimulating drugs affect test interpretation.
Synergies & Common Stacks
Both are ghrelin receptor agonists — combining would risk receptor saturation without additive benefit. Use one or the other, not both simultaneously.
If using macimorelin as a GHRP, pairing with a GHRH analog (Mod GRF) follows the same synergistic mechanism as GHRH + GHRP stacks — macimorelin provides the ghrelin-pathway pulse, CJC provides amplitude.
Dosing Quick Reference
Frequently Asked Questions
What is macimorelin used for?▼
Can macimorelin be used to boost GH therapeutically?▼
References
- Garcia JM et al. “"Macimorelin for diagnosis of adult growth hormone deficiency".” JCEM (2018). PMID: 29272514
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