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Diagnostic drug (FDA approved)Human trialsFDA approved

Macimorelin

Macimorelin acetate

Last reviewed October 27, 2026 · 28 sources · Written for general readers · Compare with another compound →

The bottom line

Macimorelin is a real FDA approved drug, but only as a one time oral test to help diagnose growth hormone deficiency in adults. It causes a short spike in growth hormone, agreed well with the older insulin test, and had few side effects, though it can affect heart rhythm. No study shows it builds muscle, burns fat or slows aging, the only repeated use trial lasted one week, and a large children's trial found it was not accurate enough for kids.

Where the evidence stands

What it is

Macimorelin is an oral drug sold in the US as Macrilen. FDA approved it in December 2017.[1]

Its only approved use is a single test to help diagnose growth hormone deficiency in adults. A person drinks it once, and blood is drawn to see how much growth hormone the pituitary releases. It is not a treatment for anything.[2]

FDA's substance registry lists macimorelin under CAS number 381231-18-1.[3] Older research papers call it by code names such as JMV-1843, EP-1572, ARD-07 and AEZS-130.[4]

The older standard test, the insulin tolerance test, works by driving blood sugar low, which can be dangerous. Macimorelin was developed as a simpler option.[5]

In the European Union it is authorized as Ghryvelin for the same use. Drugs@FDA now lists the US product's marketing status as discontinued.[6][1]

Name
Macimorelin (Macimorelin acetate)
Other names
Macrilen, Ghryvelin, AEZS-130, JMV-1843, EP-1572, ARD-07
Type
Diagnostic drug (FDA approved)
CAS number
381231-18-1
Formula
C26H30N6O3
Molecular weight
About 474.6 g/mol (free base)

What it does in the body

Macimorelin is a man made small molecule that the body does not make. It copies ghrelin, a natural hunger hormone, by switching on the ghrelin receptor in the hypothalamus and pituitary gland, which makes the pituitary release a short burst of growth hormone.[2][7]

This is the biology, area by area. A change measured in the body, like a higher blood level, does not always mean a person feels a benefit. The claims check below covers that.

Hormones

Well established

One drink makes the pituitary release growth hormone, which peaks within about an hour in healthy adults.[9][2] In adults with known growth hormone deficiency, the average peak was about seven times lower than in matched healthy adults, which is why a low result points to deficiency.[10] The burst is short. In a one week pilot of daily use in people with cancer wasting, no one reached the planned rise in IGF-1, the longer lasting hormone that growth hormone normally drives up.[11]

Other pituitary hormones

Measured in people

In 28 healthy volunteers, one drink nudged prolactin and thyroid hormone up but did not change cortisol or copeptin.[8] In 65 healthy volunteers given different pituitary tests, macimorelin did not raise oxytocin, the bonding and birth hormone.[12] A 2026 analysis found no rise in neurophysin I, a protein released together with oxytocin.[13]

Blood sugar

Measured in people

In 28 healthy adults, blood sugar stayed about flat for two hours after the drink. That is different from the glucagon and arginine tests, where blood sugar rose and then fell.[14]

Heart and blood vessels

Measured in people

Macimorelin lengthens the QT interval, the time the heart's lower chambers take to reset between beats. In healthy adults QT rose about 10 to 11 milliseconds, and in a dedicated heart safety study a high test amount lengthened it by up to about 9.6 milliseconds at four hours.[9][15] The label warns against combining it with other drugs that do this.[2]

Fat and appetite

Seen in animals

In lean mice, one injection raised food intake up to five times compared with salt water, and 10 days of injections raised food intake and body weight and switched on hunger signals in the brain.[16] In people, the only repeated use trial lasted one week, and weight change was not significantly different from placebo.[11]

Brain and nerves

Seen in animals

In kindled mice, a model of epilepsy, macimorelin lowered seizure severity, and the effect vanished in mice lacking the ghrelin receptor.[17] In a mouse model of drug resistant epilepsy, two weeks of injections cut the number and length of seizures during treatment but did not change the disease once treatment stopped.[18] This has not been studied in people.

Gut

Measured in people

It is absorbed from the gut. In 16 healthy adults, taking it with a meal cut the amount reaching the blood by about half, and the growth hormone peak came later and was only about a third as high.[19]

How it works

Macimorelin switches on growth hormone secretagogue receptors, the receptors the hunger hormone ghrelin uses, in the pituitary gland and hypothalamus. This makes the pituitary release growth hormone.[2]

  • High resolution 3D images from 2025 show macimorelin sitting in a split pocket inside this receptor, the same pocket used by the related drug anamorelin.[7]
  • In 28 healthy volunteers, one drink raised growth hormone sharply and also nudged prolactin and thyroid hormone up, but did not change cortisol or copeptin, a marker of the body's water balance hormone.[8]
  • In a placebo controlled study of 28 healthy adults, growth hormone peaked within about an hour after the drink.[9]
  • Doctors measure growth hormone in the blood after the test drink. A low peak points to growth hormone deficiency.[2][5]
  • Strong CYP3A4 inducers, drugs that speed up how the liver breaks down other medicines, can cause false positive results. Recent damage to the hypothalamus can cause false negative results.[2]

This mechanism is well established and is described on the FDA label. It produces a short spike, not a lasting rise.

What the research shows

We keep animal and human evidence apart. A result in animals is a reason to study something in people, not proof that it works in people.

Animal and lab studies

Raised appetite and calmed seizures in mice

  • In newborn rats, an injection under the skin caused a marked growth hormone rise, matching what was seen in people.[20]
  • In lean mice, a single injection raised food intake up to five times compared with salt water. Ten days of injections raised food intake, body weight and brain hunger signals, and lowered a heat making protein in brown fat.[16]
  • In kindled mice, an epilepsy model, it lowered seizure severity, but not in mice bred without the ghrelin receptor, showing the effect runs through that receptor.[17]
  • In a mouse model of drug resistant temporal lobe epilepsy, two weeks of injections reduced seizure number and length during treatment but did not stop the disease from developing, and did not change food intake or weight over two weeks.[18]
  • In rats, anti doping scientists found the main breakdown products of macimorelin in urine, which can help testing labs catch athletes who use it.[22]

Limit: These are small animal studies. The drug's approval rests on human testing, which is summarized on its FDA label.[2]

Human studies

Works as a diagnostic test; not proven as a treatment

  • The first published human test, in 2002, gave it to two healthy young men by vein and by mouth. Both routes caused a strong, selective growth hormone rise.[20]
  • In 2007, 36 healthy men took one dose by mouth or a placebo at rising strengths. Drug levels and growth hormone rose quickly, and more drug meant more growth hormone.[21]
  • In 16 healthy men and women who took it once fasting and once with a meal, food cut absorption by about half and made the growth hormone peak about a third as high.[19]
  • In a 2013 study, 50 adults with known growth hormone deficiency and 48 matched healthy adults drank macimorelin. The average growth hormone peak was about seven times lower in the deficient group. The best cutoff correctly sorted 82% of deficient and 92% of healthy people. One drug related serious event occurred, a QT change on a heart tracing with no symptoms.[10]
  • In the main trial, 157 adults took the macimorelin test and the insulin tolerance test in random order. The two tests agreed in 84% of the 140 people with both results: 94% of negative results and 74% of positive results.[2]
  • Results repeated well: about 91% to 97% of retested people got the same answer.[2][5]
  • A later analysis of that trial found accuracy held up across age, sex and body size in adults with a BMI under 37. At a higher cutoff it caught 92% of deficient people and correctly cleared 96% of healthy ones.[23]
  • In a 2026 review of 37 adults tested at one US hospital, 41% met the deficiency cutoff FDA uses and 54% met a higher cutoff. Results that changed between the two cutoffs were mostly in people with a BMI above 35.[24]
  • In a placebo controlled study of 28 healthy adults given one drink, 10 (36%) had side effects, all mild or moderate, and headache was most common. QT, a heart rhythm measure, lengthened by about 10 to 11 milliseconds at every level tested.[9]
  • In a heart safety study of 60 healthy adults who took macimorelin, placebo and a comparison drug in turn, a high test amount lengthened QT by up to about 9.6 milliseconds at four hours.[15]
  • In 24 children aged 2 to 17 in an open study, no side effects were linked to macimorelin.[25] But in a phase 3 trial of 102 children and teens who each had two macimorelin tests and two standard tests, macimorelin agreed with the standard tests only about 65% of the time, which the sponsor called surprising. Side effects occurred with macimorelin in about 12% of children, versus about 6% with arginine and 19% with clonidine.[26] FDA's label now says it was not shown to be accurate in children.[2]
  • In a one week pilot, 15 people with cancer related weight loss took a daily drink or placebo. It seemed safe, but weight, IGF-1 and quality of life did not differ significantly from placebo.[11]

Limit: The evidence supports a single diagnostic drink in adults, not repeated use for muscle, fat loss or anti aging.

Claims check

The most common claims about this compound, and what studies actually found. Verdicts rate the evidence, not whether you should use it.

Raises growth hormone

Shown in people

Yes, briefly. The first human tests, in two young men in 2002 and 36 healthy men in 2007, found a strong, rapid growth hormone rise after a single dose by mouth.[20][21] In later studies of healthy adults, including a placebo controlled one, growth hormone peaked within about an hour.[9][8] This short spike is exactly what the diagnostic test measures.[2] In a one week pilot trial in 15 people with cancer wasting, no one taking it daily reached the planned rise in IGF-1, the hormone that growth hormone normally drives up over time.[11]

Builds muscle

Not tested

No study has measured muscle growth in people taking macimorelin. The only repeated use trial lasted one week in 15 people with cancer wasting, and it tracked weight, IGF-1 and quality of life, not muscle.[11]

Burns fat

Not tested

No study has tested macimorelin for fat loss. Its trials looked at diagnosing growth hormone deficiency and, in one tiny pilot, weight gain in cancer wasting.[2][11]

Increases appetite and hunger

Only in animals

In lean mice, injections raised food intake up to five times and, over 10 days, raised body weight.[16] In mice with epilepsy, it still caused a short burst of eating.[18] No human trial has shown an appetite gain; the one week cancer wasting pilot found no significant weight difference from placebo.[11]

Helps people with cancer wasting gain weight

Mixed results

In a one week pilot, 10 people with cancer related weight loss took a daily drink of macimorelin and 5 took placebo. Results leaned toward macimorelin for weight and quality of life, but the differences were not statistically significant and no one reached the planned IGF-1 rise.[11]

Boosts energy and fights fatigue

Mixed results

Only one tiny trial looked at this. In the 15 person cancer wasting pilot, fatigue scores did not differ significantly from placebo after one week.[11]

Slows aging

Not tested

No study has tested macimorelin for aging or lifespan. FDA approved it only as a one time test.[2]

Known risks and side effects

  • Heart rhythm changes. Macimorelin lengthens the QT interval, a measure of heart rhythm, which can lead to a dangerous rhythm. In healthy volunteers QT rose by about 10 milliseconds, and the label says not to combine it with other drugs that do this.[2][9][15]
  • Mild side effects are common enough to notice. In the main adult trial an odd taste affected about 5% of people, and dizziness, headache and tiredness about 4% each, with no serious side effects. In a healthy volunteer study, 36% had a mild or moderate side effect, most often headache.[2][5][9] In the children's trial, about 12% had a side effect on macimorelin days.[26]
  • Wrong test results. Some medicines, including steroids, insulin and other growth hormone drugs, can skew the result.[2] Taking it with food blunts the response.[19] Obesity lowers the growth hormone response, which can make results harder to read.[10][24]
  • Limits on who it fits. Its safety and accuracy are not established for children or for adults with a BMI above 40. A large children's trial found it was not accurate enough.[2][26]
  • No data for repeated use. Daily use has only been tried for one week in 10 people, so long term use is untested.[11]

Regulatory status

Today: Macimorelin (Macrilen) is FDA approved only to help diagnose adult growth hormone deficiency, though Drugs@FDA lists the product as discontinued.[1][2] It is authorized in the EU as Ghryvelin. WADA bans it at all times, and its 2027 list, in force January 1, 2027, names it among growth hormone releasing factors.[6][27][28]

  1. FDA approved Macrilen as a new molecular entity for diagnosing adult growth hormone deficiency.[1]
  2. The European Commission authorized it as Ghryvelin.[6]
  3. Results of the phase 3 children's trial, which ended in June 2024, were posted in the EU trials register, showing about 65% agreement with standard tests.[26]
  4. FDA posted an updated Macrilen label, which states the test was not shown to be accurate in children.[1][2]
  5. WADA published its 2027 Prohibited List, which names macimorelin as a banned growth hormone releasing factor.[28]

Sources

  1. U.S. Food and Drug Administration. Drugs@FDA: MACRILEN, NDA 205598. Drugs@FDA
  2. Aeterna Zentaris. MACRILEN (macimorelin) for oral solution. Prescribing information, revised July 2026. U.S. Food and Drug Administration. FDA label
  3. U.S. FDA and NCATS Global Substance Registration System (GSRS). Macimorelin, UNII 8680B21W73: codes. FDA GSRS codes
  4. U.S. FDA and NCATS Global Substance Registration System (GSRS). Macimorelin, UNII 8680B21W73: names and synonyms. FDA GSRS names
  5. Garcia JM, Biller BMK, Korbonits M, Popovic V, Luger A, Strasburger CJ, et al. Macimorelin as a diagnostic test for adult GH deficiency. J Clin Endocrinol Metab. 2018;103(8):3083-3093. PMID 29860473
  6. European Medicines Agency. Ghryvelin (macimorelin). EPAR, last updated May 13, 2024. EMA
  7. Wang RL, Sun J, Liu H, Guo SM, Zhang Y, Hu W, et al. Molecular recognition of two approved drugs Macimorelin and Anamorelin by the growth hormone secretagogue receptor. Acta Pharmacol Sin. 2025;46(11):2998-3008. PMID 40542284
  8. Urwyler SA, Lustenberger S, Drummond JR, Soares BS, Vogt DR, Ammer N, et al. Effects of oral macimorelin on copeptin and anterior pituitary hormones in healthy volunteers. Pituitary. 2021;24(4):555-563. PMID 33615399
  9. Klaus B, Sachse R, Ammer N, Kelepouris N, Ostrow V. Safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in healthy adults: Results of a single-dose, randomized controlled study. Growth Horm IGF Res. 2020;52:101321. PMID 32325373
  10. Garcia JM, Swerdloff R, Wang C, Kyle M, Kipnes M, Biller BMK, et al. Macimorelin (AEZS-130)-stimulated growth hormone (GH) test: validation of a novel oral stimulation test for the diagnosis of adult GH deficiency. J Clin Endocrinol Metab. 2013;98(6):2422-2429. PMID 23559086
  11. Herodes M, Anderson LJ, Shober S, Schur EA, Graf SA, Ammer N, et al. Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia. J Cachexia Sarcopenia Muscle. 2023;14(2):835-846. PMID 36860137
  12. Sailer CO, et al. Oxytocin levels in response to pituitary provocation tests in healthy volunteers. Eur J Endocrinol. 2021;185(3):355-364. PMID 34181566
  13. Nikaj A, Atila C, Rudin D, Luethi D, Sailer CO, et al. Neurophysin-I dynamics upon different pituitary provocation tests in healthy participants. Endocr Connect. 2026;15(5):e250929. PMID 42041101
  14. Atila C, Monnerat S, Urwyler SA, Refardt J, Winzeler B, Christ-Crain M. The effect of glucose dynamics on plasma copeptin levels upon glucagon, arginine, and macimorelin stimulation in healthy adults: Data from: Glucacop, Macicop, and CARGO study. Pituitary. 2022;25(4):636-644. PMID 35723775
  15. Lissy M, Demmel V, Sachse R, Ammer N, Kelepouris N, Ostrow V. Thorough QT/QTc Study Evaluating the Effect of Macimorelin on Cardiac Safety Parameters in Healthy Participants. Clin Pharmacol Drug Dev. 2021;10(5):494-501. PMID 32961034
  16. Holubová M, Spolcová A, Demianová Z, Sýkora D, Fehrentz JA, Martinez J, et al. Ghrelin agonist JMV 1843 increases food intake, body weight and expression of orexigenic neuropeptides in mice. Physiol Res. 2013;62(4):435-444. PMID 23590608
  17. Coppens J, Aourz N, Walrave L, Fehrentz JA, Martinez J, De Bundel D, et al. Anticonvulsant effect of a ghrelin receptor agonist in 6Hz corneally kindled mice. Epilepsia. 2016;57(9):e195-e199. PMID 27378373
  18. Buckinx A, Pierre A, Van Den Herrewegen Y, Guenther E, Gerlach M, et al. Translational potential of the ghrelin receptor agonist macimorelin for seizure suppression in pharmacoresistant epilepsy. Eur J Neurol. 2021;28(9):3100-3112. PMID 34157194
  19. MacLean CM, Casanova AT, Baselgia-Jeker L, Neave N, Larsen F, Skillern L, et al. Effect of food on the pharmacokinetics and pharmacodynamics of an oral ghrelin agonist (ARD-07) in healthy subjects. J Clin Pharmacol. 2009;49(5):553-559. PMID 19293342
  20. Broglio F, Boutignon F, Benso A, Gottero C, Prodam F, Arvat E, et al. EP1572: a novel peptido-mimetic GH secretagogue with potent and selective GH-releasing activity in man. J Endocrinol Invest. 2002;25(8):RC26-8. PMID 12240910
  21. Piccoli F, Degen L, MacLean C, Peter S, Baselgia L, Larsen F, et al. Pharmacokinetics and pharmacodynamic effects of an oral ghrelin agonist in healthy subjects. J Clin Endocrinol Metab. 2007;92(5):1814-1820. PMID 17284637
  22. Lange T, Thomas A, Görgens C, Bidlingmaier M, Schilbach K, et al. Comprehensive insights into the formation of metabolites of the ghrelin mimetics capromorelin, macimorelin and tabimorelin as potential markers for doping control purposes. Biomed Chromatogr. 2021;35(6):e5075. PMID 33458843
  23. Garcia JM, Biller BMK, Korbonits M, Popovic V, Luger A, Strasburger CJ, et al. Sensitivity and specificity of the macimorelin test for diagnosis of AGHD. Endocr Connect. 2021;10(1):76-83. PMID 33320108
  24. Yadav P, Hamrahian AH, Salvatori R. Real-world diagnostic performance of the macimorelin stimulation test in the diagnosis of adult growth hormone deficiency. Pituitary. 2026;29(2):47. PMID 41793495
  25. Csákváry V, Ammer N, Bagci EB, Bolshova OV, Damholt BB, Katanic D, et al. Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Macimorelin in Children with Suspected Growth Hormone Deficiency: An Open-Label, Group Comparison, Dose-Escalation Trial. Horm Res Paediatr. 2021;94(7-8):239-250. PMID 34438400
  26. Aeterna Zentaris GmbH. Multicenter, open-label trial to investigate the efficacy and safety of a single oral dose of macimorelin acetate as a growth hormone stimulation test in pediatric patients with suspected growth hormone deficiency (AEZS-130-P02, NCT04786873). EU Clinical Trials Register, EudraCT 2018-001989-42, results posted January 1, 2025. EudraCT 2018-001989-42
  27. World Anti-Doping Agency. The 2026 Prohibited List. In force January 1, 2026. WADA 2026
  28. World Anti-Doping Agency. World Anti-Doping Code International Standard: Prohibited List 2027, section S2.2.4 Growth hormone releasing factors. In force January 1, 2027. WADA 2027
Medical disclaimer

This page is educational information only. It is not medical advice and does not replace care from a licensed medical provider. Do not use this page to decide whether to take any substance. Talk to a licensed medical provider first.

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