Macimorelin (Macrilen) is an orally active growth hormone secretagogue that received FDA approval in December 2017 as a diagnostic test for adult growth hormone deficiency (AGHD). It is the only FDA-approved oral GH secretagogue in the United States. Macimorelin works by stimulating GH release; the peak GH response is then measured to diagnose GH deficiency. It was developed by Aeterna Zentaris. Novo Nordisk held U.S. and Canadian marketing rights from 2018 until returning them to Aeterna Zentaris in 2022. Clinical trials demonstrated 92% concordance with the insulin tolerance test (ITT), the previous gold standard.
Category: Growth Hormone Secretagogue. Evidence rating: A (strong human clinical data).
Clinical status: FDA-approved (December 2017) as a diagnostic test for adult GH deficiency.
Macimorelin is a ghrelin receptor (GHS-R1a) agonist. After oral administration, it stimulates growth hormone release from the anterior pituitary in a dose-dependent manner. The GH response peaks approximately 30-90 minutes post-dose. In the diagnostic setting, a blood GH level below 2.8 ng/mL at…
Safety considerations: Common adverse reactions (>=1%): dysgeusia (taste disturbance), dizziness, headache, fatigue, nausea; Transient QTc prolongation has been observed; avoid in patients with known QT prolongation or those taking drugs that prolong QT interval; Generally well-tolerated as a single-dose diagnostic agent.
Reviewed by the PeptideAtlas Editorial Team. Last reviewed: 2026-08-12.
Related peptides: Ipamorelin, CJC-1295, Sermorelin.
Compare: Macimorelin vs Ipamorelin, Macimorelin vs CJC-1295, Macimorelin vs Sermorelin.
Macimorelin is administered as a single oral dose (0.5 mg/kg) after an overnight fast. Blood samples are drawn at 30, 45, 60, and 90 minutes post-dose. A peak GH level below 2.8 ng/mL confirms GH deficiency.
No. Macimorelin is approved solely as a diagnostic test. While it does stimulate GH release, it is designed for single-dose use in a clinical setting, not chronic administration. It is not used or studied for performance enhancement.
The pivotal trial showed 92% concordance between the two tests. Macimorelin is considered safer because it does not require induced hypoglycemia, which can be dangerous for patients with seizure disorders or cardiovascular disease.