Macimorelin
Also called Macrilen, Ghryvelin, macimorelin acetate and AEZS-1301, 6, 7
Macimorelin is a drink given once, in a clinic, to test whether an adult's pituitary gland makes enough growth hormone. It switches on the ghrelin receptor, and a doctor measures how much growth hormone the body releases in response.1 FDA approved it in 2017 as Macrilen, after a trial showed it agreed well with the older insulin tolerance test.1, 2, 4 It is not a treatment, and nobody has tested it for muscle, fat loss or anti-aging. US sales stopped in May 2023 after Novo Nordisk ended its license, and FDA now lists the product as discontinued.4, 6
Related: anamorelin, lenomorelin (ghrelin itself), MK-677 and ipamorelin act on the same receptor. See every peptide's status in the regulatory tracker.
In this guide
At a glance
| What it is | An oral growth hormone secretagogue receptor (ghrelin receptor) agonist. A small molecule built from modified amino acids1, 14 |
|---|---|
| Approved for | Diagnosing adult growth hormone deficiency. A single dose in a clinic1 |
| Best evidence | A randomized crossover trial against the insulin tolerance test: 87% sensitivity and 96% specificity at the label cut-off2 |
| Not shown | Accuracy in children. Accuracy with a BMI over 401 |
| No human evidence for | Muscle, fat loss, sleep or anti-aging. It has never been tested as a treatment for these |
| Main risks | A small QT prolongation on the ECG, taste change, dizziness, headache, nausea1 |
| US availability | Not sold. FDA's Orange Book lists Macrilen as discontinued4, 5 |
| In sport | Banned at all times (WADA S2.2.4, named)13 |
| Typical cost | No US source to price |
Where to get it
MoveWell sells nothing and earns nothing from this page. Macrilen isn't sold in the US right now. Why
Sales stopped in May 2023. FDA lists the product as discontinued, though the approval still stands.4, 6
HistoryEndocrinologists can still test for growth hormone deficiency with other stimulation tests, such as the insulin tolerance test.2, 3
How testing worksMolecular structure
A small, peptide-like molecule. It is built from aminoisobutyric acid and two tryptophan-derived units. The end unit is reversed and capped with a formyl group, so it isn't a normal peptide chain.
The reversed, formyl-capped end, which a normal peptide doesn't have
- Type
- Peptide-like small molecule, taken by mouth
- Formula
- C26H30N6O3
- Weight
- 474.6 g/mol
- Salt sold
- Macimorelin acetate
- PubChem
- CID 9804938
- Target
- Growth hormone secretagogue receptor (ghrelin receptor)
Drawn from the PubChem structure, with both chiral centres in the R form. Formula and weight are for the free base; the product contains the acetate salt.1, 14
What it is
Adults can lose growth hormone because of damage to the pituitary gland or the hypothalamus above it, for example from a tumor or a past head injury.1 To check, doctors give something that should make the pituitary release growth hormone, then measure the response. This is called a stimulation test.2
The standard has been the insulin tolerance test, which drops blood sugar on purpose. It is labor-intensive, unpleasant and can cause severe low blood sugar.3 Macimorelin was developed as a simpler option: a single drink after at least 8 hours of fasting.1
FDA first turned down the application because the main trial missed its agreed goal.9 A second trial against the insulin tolerance test led to approval on December 20, 2017.2, 4 In Europe it is sold as Ghryvelin.6
It is not ghrelin. Lenomorelin is ghrelin itself. Anamorelin and MK-677 are daily pills that act on the same receptor.
How it works
- Ghrelin receptor. It activates growth hormone secretagogue receptors in the pituitary and hypothalamus, which releases growth hormone.1
- The test. Blood is drawn several times after the dose. A peak growth hormone below 2.8 ng/mL counts as a positive test for deficiency on the label.1
- What can throw it off. Drugs that speed up the liver enzyme CYP3A4 can lower macimorelin levels and cause false positives. Recent-onset hypothalamic disease can cause false negatives.1
Evidence map
Each claimed use is graded separately. A grade measures how much evidence exists, not whether the result was good news.
FDA-approved. Agreed with the insulin tolerance test in a randomized crossover trial
One phase 3 study of 102 children. It missed its main goal
No study found. It is approved only as a single test dose
Scale: 5 FDA-approved, 4 strong human, 3 limited human, 2 animal or lab only, 1 anecdotal
Key studies
| Use | Study | Model | Finding |
|---|---|---|---|
| Adult GH deficiency | Garcia 20182 | Human RCT, crossover 157 tested, 140 with both tests1 | Against the insulin tolerance test: sensitivity 87%, specificity 96%. Repeat tests agreed 97% of the time (the label counts 31 of 34, 91%). No serious side effects from macimorelin |
| Adult GH deficiency | FDA label analysis1 | Same trial | Positive agreement 74%, negative agreement 94%, overall 84% |
| Child GH deficiency | DETECT, 20247, 1 | Human n=102, ages 3 to 17 | Main goal missed. The company blamed the comparison tests; FDA's label says accuracy in children wasn't shown |
The trials studied macimorelin as a one-dose diagnostic test only.
By goal
Pick your goal to see what the evidence supports.
| Goal | Human evidence | Result |
|---|---|---|
| Diagnose adult GH deficiency | Randomized crossover trial | Approved. Comparable to the insulin tolerance test |
| Diagnose child GH deficiency | One phase 3 study, n=102 | Not shown |
| Muscle or anti-aging | None | Unknown |
How it's used
We don't give a dose for any use other than the approved test, and this isn't instruction.
On the FDA label, a healthcare professional mixes one 60 mg pouch in water (two above 120 kg) and gives 0.5 mg per kg of body weight as a single drink, after at least 8 hours of fasting. Blood samples for growth hormone are taken at 30, 45, 60 and 90 minutes. Growth hormone treatment has to stop at least a week before.1 The label describes it as a single dose.1
Side effects and who should avoid it
- Common, mild effects. In 154 adults the most common were a change in taste (4.5%), dizziness, headache and tiredness (3.9% each), and nausea and hunger (3.2% each).1
- Heart rhythm. It raises the QTc interval by about 11 msec. Taking it with other QT-prolonging drugs can lead to a dangerous rhythm called torsade de pointes, so those drugs are stopped first.1
- Drug interactions. Strong CYP3A4 inducers such as carbamazepine, phenytoin, rifampin and St. John's wort should be stopped before the test. So should drugs that change growth hormone release, such as glucocorticoids and somatostatin.1
- Who it isn't for. Children, because accuracy wasn't shown. People with a BMI over 40, because its safety and accuracy weren't established in them.1
- Repeated or off-label use. No safety data exist for taking it more than once as a growth hormone booster.
Compared with
| Macimorelin | Anamorelin | MK-677 | Ghrelin | |
|---|---|---|---|---|
| What it is | Peptide-like small molecule | Small molecule | Small molecule | 28-amino-acid hormone |
| Taken | One drink, for a test | Daily pill | Daily pill | Injected or infused in studies |
| Approved | US and EU, as a diagnostic test | Japan, for cancer cachexia | Nowhere | Nowhere |
| Sold in the US | No, discontinued | No | No | No |
| In sport | Banned | Banned | Banned | Banned |
Sources: FDA label,1 Orange Book listing,4 Ono,16 WADA 2026 list.13 See our guides to anamorelin, MK-677, lenomorelin (ghrelin) and ipamorelin.
Stacks
Macimorelin is a one-time test dose, not something to stack. Other drugs that act on growth hormone, including ipamorelin or MK-677, would distort the test result, and the label says to stop growth hormone products beforehand.1
Myths vs evidence
All options
MoveWell sells nothing and has no commercial link on this page. Checked November 1, 2026
| Route | Status | Why |
|---|---|---|
| Prescription drug (Macrilen) | Approved, not sold | US sales stopped May 2023. Orange Book lists it as discontinued4, 6 |
| Compounding pharmacy | None found | As the ingredient of an FDA-approved drug, 503A rules don't bar it, but we found no pharmacy offering it. It isn't on FDA's bulks nomination lists10, 11 |
| Telehealth | None found | Superpower, which offers compounded peptides, doesn't list it17 |
| Other GH tests | Available | Through an endocrinologist, for example the insulin tolerance test2, 3 |
Research use only products
We don't list sellers. "Research use only" macimorelin isn't the approved product and isn't checked for purity or dose. In August 2026 FDA warned five peptide sellers that the label doesn't excuse products clearly meant for people.15
Legal status history
Newest first.
- Current statusFDA-approved for diagnosing adult growth hormone deficiency, but not sold in the US. Listed as discontinued. Not covered by the HHS peptide policy. Banned in sport.1, 4, 12, 13
- Who will hold the Macrilen rights after the German owner's expected insolvency. No US relaunch announced.8
- FDA label revised. The current label states diagnostic accuracy was not shown in a 102-patient study of children and teens.1
- COSCIENS stops funding its German drug subsidiaries, expects them to enter insolvency, and expects to surrender its Macrilen rights.8
- Pediatric DETECT trial misses its main goal.7
- US sales "temporarily discontinued" until a new partner is found.6
- Pharmanovia takes the European and UK rights to Ghryvelin.6
- Novo Nordisk announces it is ending its North American license.6
- Validation trial published.2, 3
- FDA approves Macrilen, NDA 205598.4, 5
FAQ
Is macimorelin FDA-approved?
Yes, as Macrilen, for diagnosing growth hormone deficiency in adults. It isn't approved as a treatment for anything.
Can I get it in the US?
Not right now. US sales stopped in 2023, and FDA lists the product as discontinued. Endocrinologists use other stimulation tests.
Is it a peptide?
Not quite. It's a small molecule built from modified amino acids, with a non-peptide end. That's why it works by mouth.
Will it raise my growth hormone for muscle or anti-aging?
It raises growth hormone briefly after one dose, which is how the test works. Nobody has studied repeated use for muscle or aging.
What dose is used?
Only the label's test dose, given once by a healthcare professional. We don't give a dose for any other use.
Can athletes use it?
No. WADA names macimorelin under S2.2.4, banned in and out of competition.
Is it the same as ghrelin?
No. Ghrelin, called lenomorelin as a drug name, is the natural 28-amino-acid hormone. Macimorelin is a much smaller man-made molecule that acts on the same receptor.
References
17 sources, with links
- FDA. Macrilen (macimorelin) for oral solution, prescribing information, NDA 205598 (revised Jul 2026). fda.gov
- Garcia JM, Biller BMK, Korbonits M, et al. Macimorelin as a diagnostic test for adult GH deficiency. J Clin Endocrinol Metab 2018;103(8):3083–3093. PMID 29860473
- Healio. Oral macimorelin safe diagnostic test for adult GH deficiency (Jun 8, 2018). healio.com
- DrugPatentWatch. NDA 205598, Macrilen: Orange Book status "DISCN," approved Dec 20, 2017 (page updated Nov 1, 2026). Link
- Assyro. FDA Orange Book product record: Macrilen (macimorelin acetate), NDA 205598, discontinued. Link
- TheFly via TipRanks. Aeterna Zentaris says sales of Macrilen to be temporarily discontinued in U.S. (2023). Link
- COSCIENS Biopharma. Top-line results of phase 3 DETECT trial for the diagnosis of childhood-onset growth hormone deficiency (Aug 27, 2024). Link
- COSCIENS Biopharma. COSCIENS provides strategic update (Mar 5, 2026). globenewswire.com
- The Pharma Letter. FDA declines approval of Macrilen, issuing CRL. Link
- FDA. Bulk drug substances used in compounding under section 503A of the FD&C Act (current as of May 14, 2026). fda.gov
- FDA. Bulk drug substances nominated for use in compounding under section 503A, Categories 1 to 3 (updated May 14, 2026). fda.gov
- HHS. 503A peptide enforcement discretion policy, Appendix B (Oct 28, 2026). hhs.gov
- World Anti-Doping Agency. 2026 Prohibited List, S2.2.4 growth hormone secretagogues (copy hosted by SEGAS). PDF
- PubChem CID 9804938, macimorelin (via PubChemLite). Link
- ArentFox Schiff. RUO-ined: five peptide vendors learn research use only is not a legal strategy (Sep 18, 2026; on FDA warning letters of Aug 24, 2026). Link
- Ono Pharmaceutical. ONO receives manufacturing and marketing approval of Adlumiz, a ghrelin receptor agonist, for the treatment of cancer cachexia (Jan 22, 2021). ono-pharma.com
- Superpower. Peptides page (checked Nov 1, 2026; macimorelin and other ghrelin-receptor drugs not listed). Link
This page is for education and is not medical advice. Macrilen is approved only as a diagnostic test. Talk to an endocrinologist if you think you have a growth hormone problem.