Macimorelin is a small-molecule drug that tricks the pituitary into releasing growth hormone, then doctors measure how much comes out. It is a diagnostic tool, not a treatment. Approved by the FDA in December 2017 under the brand name Macrilen (sold in Europe as Ghryvelin), it was the first oral test cleared for diagnosing adult growth hormone deficiency. You will also see it under research codes: AEZS-130, JMV-1843, EP-1572, and ARD-07.
The compound was first synthesized at the University of Montpellier and developed by Aeterna Zentaris. Chemically it is a synthetic peptidomimetic, an orally active ghrelin mimic.
How it works
Macimorelin binds the growth hormone secretagogue receptor (GHS-R1a), the same receptor the hormone ghrelin uses. It binds with affinity similar to ghrelin and stimulates the pituitary and hypothalamus to release growth hormone acutely (PubChem, validation study, J Clin Endocrinol Metab 2013). That short-lived spike is the whole point of the test: if the pituitary can produce a normal surge after the drug, the patient probably is not deficient.
How the test is used
The patient drinks a single weight-based oral dose (0.5 mg/kg). Blood is then drawn at set intervals over about 90 minutes, and peak growth hormone is compared against a diagnostic cutoff. A blunted response points toward deficiency.
The appeal is what it replaces. The long-standing reference test, the insulin tolerance test, deliberately drives the patient into hypoglycemia and is contraindicated in people with coronary disease or seizure disorders. Macimorelin avoids that. The FDA noted agreement between the macimorelin test and the insulin tolerance test in 84% of subjects overall, rising to 89% among those judged most likely to be deficient before testing.
What the research found
The pivotal validation work is documented in peer-reviewed literature. In a multicenter study of 50 adults with growth hormone deficiency and 48 matched healthy controls, an optimal cutoff of 2.7 ng/mL gave 82% sensitivity and 92% specificity, performance the authors called comparable to the arginine-plus-GHRH test (Garcia et al., 2013). The most notable drug-related serious event was asymptomatic QT-interval prolongation, which is why the label carries a QT warning and why interacting drugs and the test itself need care.
A pediatric program (the DETECT trial) studied the test in children with suspected growth hormone deficiency. U.S. sales of Macrilen were temporarily suspended in 2023 during that work (Aeterna Zentaris / BioSpace).
Regulatory and anti-doping status
Macimorelin is a prescription diagnostic, approved in both the U.S. and the EU for that single purpose. It is not a therapy for growth hormone deficiency and it is not a performance or anti-aging product. In sport, it is banned. The World Anti-Doping Agency lists growth hormone secretagogues and their mimetics under section S2 of the Prohibited List, which covers macimorelin (WADA Prohibited List).
The quality angle
Because macimorelin shows up on the gray-market peptide and research-chemical scene, the buyer-side question is identity and purity, not branding. Material sold outside the regulated supply chain has no FDA-reviewed manufacturing behind it. A certificate of analysis from an independent lab (showing identity by mass spec and purity by HPLC) is the minimum evidence that a vial contains what the label claims. peptideone aggregates third-party COAs and vendor ratings precisely because that documentation, not marketing copy, is what separates verified material from guesswork.
Nothing here is medical or dosing advice. Macimorelin is an approved diagnostic administered by clinicians; any non-clinical material is research-use-only and not for human consumption.