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Diagnostic drug (FDA approved)Human trialsFDA approved

Macimorelin

Macimorelin acetate

Last reviewed October 27, 2026 · 14 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, and the only repeated use trial lasted one week.

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]

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.[4]

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.[5][1]

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

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]

  • 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.[6]
  • In a placebo controlled study of 28 healthy adults, growth hormone peaked within about an hour after the drink.[7]
  • Doctors measure growth hormone in the blood after the test drink. A low peak points to growth hormone deficiency.[2][4]
  • 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

Not the main evidence for this drug

  • Macimorelin's approval rests on human testing, which is summarized on its FDA label.[2]

Limit: Animal studies add little to what the human trials and label show.

Human studies

Works as a diagnostic test; not proven as a treatment

  • In a 2013 study, 50 adults with known growth hormone deficiency and 48 matched healthy adults drank macimorelin. Peak growth hormone averaged about 2.4 ng/mL in the deficient group and 17.7 ng/mL in healthy people. 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.[9]
  • 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][4]
  • 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.[10]
  • 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.[11]
  • 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.[7]
  • 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.[12]
  • In 24 children aged 2 to 17 in an open study, no side effects were linked to macimorelin.[13] But in a later study of 102 children and teens, the test was not shown to be accurate, so it is not approved for 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.[8]

Limit: The evidence supports a single diagnostic drink, 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. In studies of healthy adults, including a placebo controlled one, a single drink made growth hormone peak within about an hour.[7][6] 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.[8]

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.[8]

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][8]

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 IGF-1 did not change.[8]

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.[8]

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][7][12]
  • Mild side effects are common enough to notice. In the main 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][4][7]
  • Wrong test results. Some medicines, including steroids, insulin and other growth hormone drugs, can skew the result.[2] Obesity lowers the growth hormone response, which can make results harder to read.[9][11]
  • Limits on who it fits. Its safety and accuracy are not established for children or for adults with a BMI above 40.[2]
  • No data for repeated use. Daily use has only been tried for one week in 10 people, so long term use is untested.[8]

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, and WADA bans it at all times.[5][14]

  1. FDA approved Macrilen as a new molecular entity for diagnosing adult growth hormone deficiency.[1]
  2. The European Commission authorized it as Ghryvelin.[5]
  3. FDA posted an updated Macrilen label, which states the test was not shown to be accurate in children.[1][2]

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. FDA GSRS
  4. 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
  5. European Medicines Agency. Ghryvelin (macimorelin). EPAR, last updated May 13, 2024. EMA
  6. 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
  7. 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
  8. 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
  9. 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
  10. 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
  11. 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
  12. 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
  13. 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
  14. World Anti-Doping Agency. The 2026 Prohibited List. In force January 1, 2026. WADA 2026
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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