Evidence review: Open Peptide Project (verified against primary PubMed, ClinicalTrials.gov & FDA records) · Last checked 2026-10-27. ← Back to Evidence Library

Macimorelin (Macrilen): what the evidence says

Name: Macimorelin (Macrilen)
Published: 2026-10-27

At a glance

What it is: an oral ghrelin-receptor agonist (a peptidomimetic, not a true peptide) that briefly makes the pituitary release growth hormone. FDA-approved in Dec 2017 as Macrilen, a drink used once to test whether an adult has GH deficiency. ^{R1, R2}

What the evidence says: in the phase 3 trial against the insulin tolerance test (the older gold standard), the macimorelin test agreed well: sensitivity 87% and specificity 96% at the label cutoff. ^R3 It is not approved or studied as a treatment.

Biggest risks: QT prolongation on ECG; strong CYP3A4 inducers can cause false positives; recent-onset hypothalamic disease can cause false negatives. ^R2

Rating


Human Human evidence	Strong for diagnostic accuracy in adults (phase 3 vs ITT) ^{R3, R4} · Limited pediatric data ^R5 · No human data as a treatment
Animal Animal / lab evidence	Not reviewed for this page
Regulatory	FDA-approved diagnostic (NDA 205598) · not on the 503A/503B lists or FDA's safety-risk page · WADA 2026: named under S2.2.4 ^{R1, R6, R7, R8, R9}
Established human dose	Label diagnostic dose (see Study details and the FDA label). No treatment dose exists

Evidence verdict: Diagnosing adult growth hormone deficiency: Strong (FDA-approved diagnostic, phase 3 vs insulin tolerance test) · Treatment, muscle, anti-aging: No human data

This page reports what studies used. It is not dosing advice.

Legend: HUMAN data · ANIMAL / LAB data · UNKNOWN · UNVERIFIED: not yet confirmed against a primary source

About the evidence: the pivotal and post-hoc studies were sponsored by Aeterna Zentaris. Safety and effectiveness are not established in people with BMI over 40. ^{R3, R2}

What is it?

Doctors test for adult GH deficiency by provoking GH release and measuring it. Macimorelin does this by mouth, avoiding the low blood sugar the insulin tolerance test causes. ^R2 Related pages: Anamorelin, Ipamorelin, MK-677.

Does it work?

Human Phase 3 (Garcia 2018): vs ITT, sensitivity 87% and specificity 96% at a 2.8 ng/mL GH cutoff; 92% and 96% at 5.1 ng/mL. ^{R3, R10}
Human Post-hoc analysis (Garcia 2021): supported the cutoff choices. ^R4
Human Children (2021): 24 children with suspected GHD; drug levels and GH response studied. ^R5 Pediatric phase 3 completed in 2024 without posted results. ^R11

Is it safe?

Human Label warnings: QT prolongation (avoid with other QT-prolonging drugs); test accuracy problems with CYP3A4 inducers and recent hypothalamic disease. ^R2
Unknown No data on repeated or long-term use; it is designed as a single test.

Gray-market "macimorelin": extra risks

A gray-market vial has no quality control and no guarantee of identity, strength or sterility. We test retail vials blind under the Open Peptide Standard; see /tests/. A passing test covers one batch on one date and does not mean the compound is safe. Repeated use as a "GH booster" has never been studied.

Is it legal?

US (FDA): prescription diagnostic, given after an 8-hour fast under medical supervision. ^{R2, R1}
Athletes: WADA 2026 names macimorelin under S2.2.4. ^R9

Study details

These are amounts researchers used, not recommendations.

Study	People / model	Route	Amount used	Follow-up	Reported	Citation
FDA label (Macrilen)	Adults tested for GHD	Oral solution, single dose after 8-h fast	0.5 mg/kg	GH sampled over 90 min	Diagnostic	FDA label
Garcia 2018 (phase 3)	Adults with suspected GHD	Oral, single dose	0.5 mg/kg	Single test	Sens 87% / spec 96%	PMID 29860473
Pediatric 2021	24 children	Oral, single dose	0.25, 0.5 or 1.0 mg/kg	Single test	PK and GH response	PMID 34438400

Full reference list (PubMed, CT.gov, FDA and WADA checked Oct 26, 2026)

^R1 Drugs@FDA, Macrilen, Aeterna Zentaris, approved Dec 20, 2017, application 205598 (openFDA drugsfda record checked Oct 26, 2026). https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=205598
^R2 Macrilen (macimorelin) oral solution prescribing information, label published Feb 19, 2026 (DailyMed, checked Oct 26, 2026). https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=aeb30f1a-4815-47ae-a2cb-b6b4e26372e1
^R3 Garcia JM, et al. J Clin Endocrinol Metab. 2018. PMID 29860473
^R4 Garcia JM, et al. Endocr Connect. 2021. PMID 33320108
^R5 Csákváry V, et al. Horm Res Paediatr. 2021. PMID 34438400
^R6 FDA, 503A bulk drug substances categories list (updated May 14, 2026). https://www.fda.gov/media/94155/download
^R7 FDA, 503B bulk drug substances categories list (updated Mar 21, 2025). https://www.fda.gov/media/94164/download
^R8 FDA, Certain bulk drug substances for use in compounding that may present significant safety risks (content current Apr 22, 2026). https://www.fda.gov/drugs/human-drug-compounding/certain-bulk-drug-substances-use-compounding-may-present-significant-safety-risks
^R9 WADA. The 2026 Prohibited List, S2.2.4. https://www.wada-ama.org/sites/default/files/2025-09/2026list_en_final_clean_september_2025.pdf
^R10 ClinicalTrials.gov NCT02558829, Aeterna Zentaris, macimorelin vs insulin tolerance test in adult GHD, phase 3, completed (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT02558829
^R11 ClinicalTrials.gov NCT04786873, Aeterna Zentaris, pediatric GHD diagnostic, phase 3, completed Jun 2024, no results posted (CT.gov API v2, checked Oct 26, 2026). https://clinicaltrials.gov/study/NCT04786873

Disclaimer

This page is for education and harm reduction, not medical advice or a recommendation to use Macimorelin (Macrilen). It is a one-time diagnostic test given under medical supervision, not a treatment. Talk to your endocrinologist, especially if you have a heart rhythm problem or take drugs that affect CYP3A4. Report problems to FDA MedWatch (https://www.fda.gov/safety/medwatch).