Macimorelin
Macrilen (brand), AEZS-130, ARD-07, EP-01572, JMV 1843, macimorelin acetate
1What it is
Diagnosing adult growth hormone deficiency is awkward: GH is released in pulses, so a random blood test tells you nothing, and the standard "gold" test, the insulin tolerance test, involves deliberately inducing hypoglycaemia under supervision. Alternatives such as GHRH-plus-arginine disappeared when GHRH products were withdrawn in the US. Macimorelin was developed (originally in France, then by Aeterna Zentaris, now marketed by Novo Nordisk) to fill that gap: a single oral drink that provokes GH release, with a blood test to see how much came out.
It is a small, chemically modified tripeptide-like molecule, orally bioavailable and much longer-acting than ghrelin. It was approved by the FDA in December 2017 and by the EMA in January 2019 for adults; paediatric studies have been conducted and a paediatric indication was under review in some regions at the time of writing †.
It appears on this site because it is a ghrelin receptor named on the WADA list alongside ipamorelin and anamorelin, and because it is sometimes mentioned as a potential oral GH for other purposes. The repeated-dose literature is very thin.
2How it's thought to work
Macimorelin binds and activates on pituitary somatotrophs, releasing stored GH, and acts in the hypothalamus to boost GHRH and suppress somatostatin. In a healthy pituitary this yields a sharp GH peak within an hour. In someone with GH deficiency — because of pituitary disease, surgery, radiotherapy or traumatic brain injury — the response is blunted. The approved cut-off in the US is a peak GH of 2.8 ng/mL: below that supports a diagnosis of adult GHD; the EU label uses a higher cut-off with different performance characteristics †.
Like other ghrelin mimetics it also stimulates appetite and produces transient small rises in cortisol and prolactin, which is irrelevant for a single diagnostic dose but relevant to any repeated use.
3What the research shows
Diagnostic accuracy for adult GH deficiency
Paediatric diagnosis
Cancer cachexia (repeated dosing)
Body composition, sleep, performance
4Reported side effects and interactions
Literature-reported
Literature (single diagnostic dose). altered taste (dysgeusia, ~5%), dizziness, headache, fatigue, nausea, hunger, feeling hot, diarrhoea, upper respiratory symptoms; all mild and transient. A small, transient increase in QTc was seen in a thorough QT study, so the label warns against use with QT-prolonging drugs and in people with long QT.
Label warnings. QT prolongation; false results if tested too soon after starting GH replacement (stop GH at least a week before); reduced GH response and risk of false-positive diagnosis with CYP3A4 inducers (carbamazepine, rifampicin, St John's wort — stop beforehand); untreated hypothyroidism or cortisol deficiency, recent GH-affecting drugs and high BMI can also blunt the response and lead to misdiagnosis.
Community-reported
essentially none; the product is dispensed for a single supervised test.Theoretical (repeated use). GH/IGF-1 class concerns — insulin resistance, fluid retention, appetite increase, caution with active malignancy — plus unknown effects of chronic QT-affecting exposure. Unstudied.
Interactions. strong CYP3A4 inducers reduce exposure; QT-prolonging drugs (certain antiarrhythmics, antipsychotics, antibiotics) are to be avoided around the test; GH, somatostatin analogues, glucocorticoids and some other hormones alter the GH response and must be managed before testing.
Markers researchers commonly monitor
For the approved diagnostic use, monitoring is the test itself: For any repeated, off-label use, the GH-secretagogue set applies (IGF-1, fasting glucose, HbA1c, blood pressure, lipids), with no data to interpret them against.
| Marker | Why it's watched |
|---|---|
| Serum GH at 30, 45, 60 and 90 minutes | the peak value is the result; sample timing matters. |
| IGF-1 (baseline) | interpreted alongside the stimulation result; a low IGF-1 with a low peak GH is the typical GHD picture. |
| ECG (QTc) before testing | per the label, in anyone with cardiac history or on QT-affecting drugs. |
| TSH/free T4 and morning cortisol before testing | untreated thyroid or adrenal deficiency blunts GH response and must be corrected first. |
| Body mass index | obesity suppresses GH response and is a known cause of false positives; the trials noted lower cut-off performance in higher BMI. |
Free for everyone. Safety information is never behind a paywall.
5Formulation and handling
Approved product is a sachet of 60 mg granules dissolved in 120 mL of water (0.5 mg/mL), with the dose volume calculated from body weight and drunk within 30 minutes of mixing, after an 8-hour fast with water only; blood draws follow at 30, 45, 60 and 90 minutes. It is a clinic procedure, not a self-administered product. Research powders are rare. No calculator link is offered.
6Commonly studied alongside
In diagnostics, compared against the insulin tolerance test, the GHRH-arginine test and glucagon stimulation. Mechanistically grouped with ipamorelin, GHRP-2 (pralmorelin — an approved injectable GH diagnostic in Japan), anamorelin, capromorelin and MK-677 / ibutamoren. In paediatric work, compared with arginine and clonidine stimulation.
Informational cross-links. Not stack recommendations.
7Regulatory status by region
| Region | Status (checked —) |
|---|---|
| United States | FDA-approved (Macrilen, December 2017) for the diagnosis of adult growth hormone deficiency; prescription-only |
| European Union | EMA-authorised (January 2019) for the same indication |
| United Kingdom | Licensed, following EU authorisation; prescription-only † |
| Australia | Not registered with the TGA as of review date † |
| South Africa | Not registered † |
| Sport | Prohibited by WADA (S2 — macimorelin is named as an example of a ghrelin mimetic); a therapeutic use exemption would be needed even for a diagnostic test |
8Open questions
- Optimal cut-offs across BMI, age and sex; the US and EU labels already differ.
- Paediatric approval and performance versus traditional two-test diagnosis †.
- Whether repeated dosing has any therapeutic use; the one-week cachexia pilot was never followed up at scale.
9References
- 1Garcia JM et al. (2013). Macimorelin (AEZS-130)-stimulated growth hormone test: validation of a novel oral stimulation test for the diagnosis of adult growth hormone deficiency. J Clin Endocrinol Metab. PubMed · DOI
- 2Garcia JM et al. (2018). Macimorelin as a diagnostic test for adult GH deficiency. J Clin Endocrinol Metab. PubMed · DOI
- 3Broglio F et al. (2002). EP1572: a novel peptido-mimetic GH secretagogue with potent and selective GH-releasing activity in man. J Endocrinol Invest. PubMed · DOI
- 4Novo Nordisk / Aeterna Zentaris. Macrilen (macimorelin) prescribing information (current US label); EMA summary of product characteristics for Macimorelin Aeterna Zentaris. PubMed
- 5Yuen KCJ et al. (2019). American Association of Clinical Endocrinologists and American College of Endocrinology guidelines for management of growth hormone deficiency in adults and patients transitioning from pediatric to adult care. Endocr Pract — for diagnostic context. PubMed · DOI
References are being resolved to PubMed/DOI identifiers; links search PubMed for the citation until then.
† Being confirmed by our reviewers against current sources.
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Self-reported side effects Phase 2
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