Library / Growth hormone

Macimorelin

Also known as Macrilen, Ghryvelin

Approved medicine

Not a peptide in the strict sense: an oral peptidomimetic ghrelin receptor agonist. Approved only as a one off diagnostic test for adult growth hormone deficiency, not as a treatment.

Not approved in Australia. Macimorelin is not on the Australian Register of Therapeutic Goods and is no longer marketed in the United States. Only a prescriber can decide whether a medicine suits you and at what dose. This page is information, not a recommendation.

Background

Macimorelin is a small, orally active ghrelin mimetic developed by Aeterna Zentaris and approved by the FDA in 2017 as Macrilen, later marketed in the US by Novo Nordisk. It was developed as a simpler and safer alternative to the insulin tolerance test for diagnosing adult growth hormone deficiency.

How it is thought to work

Taken as a single oral dose, it switches on the ghrelin receptor in the pituitary, which triggers a short burst of growth hormone release. Blood growth hormone levels are then measured; a low response suggests growth hormone deficiency.

What is claimed, and the evidence

Claim	Evidence	Notes
Diagnosis of adult growth hormone deficiency (single test dose)	Approved use	FDA approved as Macrilen. In a validation trial it had 87 to 92 per cent sensitivity and 96 per cent specificity against the insulin tolerance test, depending on the cut off.
Muscle building, fat loss or anti ageing through raised growth hormone	No published evidence	No trials of repeated use for these purposes; it is approved only as a one off diagnostic test.

Side effects

Effect	How often	Notes
Altered taste (dysgeusia)	Common	4.5 per cent in the label study of 154 people.
Dizziness, headache, fatigue	Common	About 4 per cent each in the label study.
Nausea, hunger, diarrhoea	Common	About 2 to 3 per cent each in the label study.
Feeling hot, sweating, upper respiratory infection	Uncommon	About 1 to 2 per cent in the label study.
Slow heart rate (sinus bradycardia)	Uncommon	Listed among label adverse reactions.
QT prolongation Serious	Frequency unknown	Label: increases QTc by about 11 msec; avoid other QT prolonging drugs because of the risk of torsade de pointes.

Warnings

The label warns of QT prolongation, which can lead to a dangerous heart rhythm, especially with other QT prolonging drugs.
Strong CYP3A4 inducers can cause false positive results; recent onset hypothalamic disease can cause false negatives.
Approved only as a supervised single dose diagnostic test; the US product is listed as discontinued and it is not on the ARTG.

Regulatory status

Australia: Not found on the ARTG. Likely captured by the Schedule 4 growth hormone secretagogue class entry (Not verified).
United States: FDA approved (Macrilen, 2017) as a diagnostic test for adult growth hormone deficiency; Drugs@FDA lists the product as discontinued.

Sources

Also in Growth hormone

From the VialOwl library, reviewed 26 September 2026. For education and general information. It is not medical advice and not a recommendation to use Macimorelin.