Peptide LibraryMacimorelin
Macimorelin is an FDA-approved oral ghrelin receptor agonist in the Growth Hormone Secretagogue class. Macimorelin is a small peptidomimetic agonist at the growth hormone secretagogue receptor 1a in the pituitary and hypothalamus, the same receptor targeted by ghrelin.
For research use only.
Key Facts
- CAS
- 381231-18-1
- Molecular Weight (MW)
- 474.6 g/mol
- Half-life
- —
- FDA status
- Approved
- Evidence level
- FDA Approved
- Human dose established
- Yes
- Administration Route
- Oral
- Frequency
- Single dose per test
- Last updated
- Nov 7, 2026
- Reviewed
- Nov 7, 2026
Research summary
Orally active ghrelin receptor agonist approved as a diagnostic agent for adult growth hormone deficiency. It is the first oral alternative to the insulin tolerance test for this indication.
Research evidence
- Regulatory review (FDA label)1 reviewed source
- Controlled human trials2 reviewed sources
- Early or uncontrolled human studiesNone in reviewed sources
- Lab & animal studiesNone in reviewed sources
How it works
Each step shows whether the sources Peptide Library has reviewed include that kind of research. Counts are reviewed sources, not every study ever published. Reviews and programme summaries that describe human use are shown as "reported", not as trials, and registered trials without published results are listed but not counted. A higher step means research has progressed further; it does not mean a compound works better or is safer. Compounds whose evidence has not been reviewed yet show "Not reviewed" instead of a guess.
Peptide Library's Macimorelin profile summarises 5 cited studies listed in the Science section, the compound's regulatory status, and research-protocol parameters reported for it. It is a research reference, not medical advice.
Macimorelin dosage evidence
Macimorelin has an FDA-approved human dosage as a single oral diagnostic dose for adult growth hormone deficiency. The MACRILEN label dose is 0.5 mg/kg taken as a solution after fasting for at least 8 hours, with growth hormone measured at 30, 45, 60 and 90 minutes; a peak below 2.8 ng/mL confirms the deficiency. Its safety and efficacy in children have not been established.
| Human dosing established | Yes |
|---|---|
| Studied dose range | 0.5 mg/kg as a single oral dose (diagnostic test) |
| Route | Oral |
| Frequency | Single dose per test |
| Duration studied | One diagnostic test; blood sampled up to 90 minutes |
| Evidence level | FDA Approved |
| Last reviewed | 2026-11-07 |
Research-reported dosing
Doses as studied, one row per regimen. Different trials used different regimens; they are listed separately rather than averaged.
| Study / context | Population | Dose | Route | Frequency | Duration | Outcome studied | Source |
|---|---|---|---|---|---|---|---|
| FDA label — MACRILEN, adult growth hormone deficiencyFDA-approved label · FDA prescribing information | Adults being tested for growth hormone deficiency | 0.5 mg/kg | Oral solution, after fasting for at least 8 hours | Once | Growth hormone sampled at 30, 45, 60 and 90 minutes | Maximally stimulated growth hormone below 2.8 ng/mL confirms adult growth hormone deficiency | MACRILEN (macimorelin) for oral solution — FDA prescribing information (Aeterna Zentaris), DailyMed |
| Pivotal diagnostic trial against the insulin tolerance test (Garcia et al., 2018)Clinical trial · Multicentre open-label randomised crossover trial | Adults with high (n=38), intermediate (n=37) and low (n=39) likelihood of growth hormone deficiency, and matched healthy controls (n=25) | Single oral dose; the amount is not stated in the indexed abstract | Oral | Once, repeated in a crossover with the insulin tolerance test | Single test | At a 2.8 ng/mL cutoff: sensitivity 87%, specificity 96%; reproducibility 97% on retesting (n=33) | Garcia JM et al. Macimorelin as a Diagnostic Test for Adult GH Deficiency. J Clin Endocrinol Metab. 2018. |
| Pilot trial in cancer cachexia (Herodes et al., 2023)Clinical trial · Randomised placebo-controlled pilot trial | Patients with cancer cachexia (10 on macimorelin, 5 on placebo) | 0.5 or 1.0 mg/kg, or placebo | Oral | Daily | 1 week | No related adverse events; body weight and quality of life improved numerically but not significantly against placebo | Herodes M et al. Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia. J Cachexia Sarcopenia Muscle. 2023. |
Where sources disagree
- The only labelled use is a one-time diagnostic test. Daily dosing for cachexia was tested only in a 1-week pilot of 15 patients and is not an approved use.
- The label warns that MACRILEN increases the corrected QT interval by about 11 msec and advises avoiding drugs that prolong QT. It says to stop growth hormone therapy at least one week before the test, stop strong CYP3A4 inducers, and replace other missing pituitary hormones first.
- DailyMed carries two MACRILEN listings with the same dosage: Aeterna Zentaris (cited here) and Novo Nordisk.
Sequence & molecular data
| Molecular formula | C26H30N6O3 |
|---|---|
| Molecular weight | 474.6 g/mol |
| CAS number | 381231-18-1 |
| PubChem CID | 9804938 |
| FDA UNII | 8680B21W73 |
| ChEMBL | CHEMBL278623 |
| DrugBank | DB13074 |
Identifiers link to the public PubChem, FDA Substance Registration (UNII), ChEMBL and DrugBank records for the same entity.
Science
Mechanism of Action
Macimorelin is a small peptidomimetic agonist at the growth hormone secretagogue receptor 1a in the pituitary and hypothalamus, the same receptor targeted by ghrelin. Receptor activation stimulates growth hormone release, and the peak GH concentration after a weight-based oral dose distinguishes patients with adult growth hormone deficiency from those with intact somatotroph reserve.
Studies
- Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia
- Safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in healthy adults: Results of a single-dose, randomized controlled study
- Macimorelin as a Diagnostic Test for Adult GH Deficiency
- The macimorelin-stimulated growth hormone test for adult growth hormone deficiency diagnosis
- Real-world diagnostic performance of the macimorelin stimulation test in the diagnosis of adult growth hormone deficiency
Research statistics
34 PubMed publications · 50.0% human clinical research · 6 registered trials
Counts of published research through 2026-11-01, not evidence that it works. Publications by year, study types and trials · How publications are counted
Regulatory & research status
Macimorelin is an FDA-approved product for specific labelled indications. Approval does not extend to the research contexts described on this page, and approved products are prescription medicines.
| FDA status | Approved |
|---|---|
| Research status | Approved product (see FDA status) |
| Availability | Prescription-Only |
| WADA (sport) | Unknown / Not Listed |
| Library classification | FDA-Approved |
How FDA approval, compounding and research-only status differ
Benefits
—
Macimorelin side effects
No side effects listed yet for this entry.
Storage & stability
This compound is not supplied as a powder to be mixed, so the freeze-dried powder and reconstitution handling described for research peptides does not apply. Storage conditions are product-specific: follow the label or packaging of the product itself.
Macimorelin: frequently asked questions
What is Macimorelin?
Orally active ghrelin receptor agonist approved as a diagnostic agent for adult growth hormone deficiency. It is the first oral alternative to the insulin tolerance test for this indication.
How does Macimorelin work?
Macimorelin is a small peptidomimetic agonist at the growth hormone secretagogue receptor 1a in the pituitary and hypothalamus, the same receptor targeted by ghrelin. Receptor activation stimulates growth hormone release, and the peak GH concentration after a weight-based oral dose distinguishes patients with adult growth hormone deficiency from those with intact somatotroph reserve.
Is Macimorelin FDA approved?
Yes. Macimorelin is approved by the FDA, and approved products are prescription medicines. Approval is always for specific indications studied in clinical trials, so an approved status does not mean the compound is approved for every use it is discussed for. Research-chemical material sold under the same name is not the approved product.
What peptides are similar to Macimorelin?
Compounds most often compared with Macimorelin include MK-677, Anamorelin, Tabimorelin and Relamorelin. They are grouped by shared mechanism or research area rather than by equivalence, and their regulatory status and evidence base differ.
References
- Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia — J Cachexia Sarcopenia Muscle, 2023External reference
- Safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in healthy adults: Results of a single-dose, randomized controlled study — Growth Horm IGF Res, 2020External reference
- Macimorelin as a Diagnostic Test for Adult GH Deficiency — J Clin Endocrinol Metab, 2018External reference
- The macimorelin-stimulated growth hormone test for adult growth hormone deficiency diagnosis — Expert Rev Mol Diagn, 2014External reference
- Real-world diagnostic performance of the macimorelin stimulation test in the diagnosis of adult growth hormone deficiency — Pituitary, 2026External reference
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Compiled by Peptide Library Editorial · Reviewed Aug 30, 2026 · Updated Nov 7, 2026 · Version 2
This Macimorelin profile is compiled from published literature (5 cited studies linked above), public regulatory records and chemical registries. It describes what research reports; it is not medical advice, and nothing here is a dosing recommendation for humans. Peptide Library does not sell peptides. Editorial policy · How profiles are compiled · Report an error
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