Approved & therapeutic
Macimorelin
Macrilen
Macimorelin is an orally administered growth hormone secretagogue receptor agonist approved as a diagnostic agent for adult growth hormone deficiency. It is a single-use diagnostic test, not a treatment. The application remains approved, but the only product is listed as Discontinued in Drugs@FDA, no generic exists, and US commercial sales were discontinued in May 2023 with no confirmed relaunch — so it is approved but not currently marketed in the US.
- Status
- Macimorelin is approved by the U.S. FDA and has official prescribing information.
- Evidence
- Approved labeling. Official prescribing information exists, based on clinical trials in people.
- Half-life
- Mean terminal half-life of approximately 4.1 hours after a single oral dose in healthy subjects.
- How it's taken
- Oral solution, reconstituted from granules
- Mechanism
- Growth-hormone secretagogue
- Pathways
- GH-releasing peptide, GH axis
How Macimorelin works
Macimorelin activates growth hormone secretagogue receptors in the pituitary and hypothalamus, the same receptors targeted by ghrelin, provoking release of growth hormone. Serum growth hormone is then measured at set intervals after the oral dose; a maximally stimulated level below the defined threshold supports a diagnosis of adult growth hormone deficiency.
What research has looked at
- In the pivotal randomized, open-label, cross-over study against the insulin tolerance test (140 subjects with data on both tests), the pre-specified primary analysis showed negative agreement of 94 percent (lower 95 percent confidence bound 85 percent) and positive agreement of 74 percent (lower bound 63 percent), with overall agreement of 84 percent.
- A published analysis of the same study reported sensitivity of about 87 percent and specificity of about 96 percent, but these were secondary estimates that assumed everyone in the high-likelihood group truly had growth hormone deficiency and every healthy control truly did not; they were not the primary endpoint and there was no independent standard of truth.
- Repeatability in the prescribing information was 91.2 percent: 31 of 34 subjects who took the test twice got the same result. The published report described reproducibility of 97 percent in a slightly different subset.
- Provides an oral stimulation test, avoiding the induced hypoglycemia required by the insulin tolerance test. In the pivotal study, 17.2 percent of insulin tolerance tests failed because severe hypoglycemia could not be induced, versus 0.6 percent of macimorelin tests failing for a technical error.
- Approved specifically for the diagnosis of adult growth hormone deficiency. It is not approved for children.
Evidence level: Approved labeling. Official prescribing information exists, based on clinical trials in people. These are areas studied or reported, not promised effects.
Reported side effects and risks
- Prolongs the corrected QT interval by roughly 11 msec; QT prolongation can lead to torsade de pointes ventricular tachycardia, and concomitant use with drugs known to prolong the QT interval, including certain antipsychotics, antiarrhythmics and antibiotics, is to be avoided.
- Diagnostic performance is weakest in the patients where testing is most ambiguous: in the combined intermediate and low likelihood groups of the pivotal study, positive agreement with the insulin tolerance test was 61 percent (lower 95 percent confidence bound 43 percent), 67 percent in the intermediate group and 33 percent in the low likelihood group. A negative macimorelin result does not reliably rule out growth hormone deficiency in these patients.
- Strong CYP3A4 inducers lower macimorelin concentrations and can cause a false positive test result; they must be stopped and allowed to wash out before testing.
- False negative results are possible in recent-onset hypothalamic disease, because deficiency caused by a hypothalamic lesion may not be detectable early in the disease process; repeat testing may be warranted.
- Commonly reported reactions include dysgeusia, dizziness, headache, fatigue, nausea, hunger, diarrhea, upper respiratory tract infection, feeling hot, hyperhidrosis, nasopharyngitis and sinus bradycardia.
- Safety and diagnostic performance have not been established in people with a body mass index above 40. Growth hormone therapy must be stopped at least one week before testing, other drugs affecting growth hormone secretion avoided, and deficient sex, thyroid and glucocorticoid hormones adequately replaced, or the test can mislead. This is a diagnostic agent with no approved therapeutic use; it is not indicated for raising growth hormone as a treatment.
Sources
- PubMed research on Macimorelin · NIH · National Library of Medicine
- DrugBank record for Macimorelin · DrugBank
- Active clinical trials for Macimorelin · U.S. National Library of Medicine
Track Macimorelin in Peptide Vault
Log every dose, set reminders on your own schedule, rotate injection sites and keep your vials organized. Peptide Vault records what you enter. It doesn't recommend compounds or doses. iPhone, on-device.
Related compounds
Macimorelin FAQ
What is Macimorelin?
Macimorelin is an orally administered growth hormone secretagogue receptor agonist approved as a diagnostic agent for adult growth hormone deficiency. It is a single-use diagnostic test, not a treatment. The application remains approved, but the only product is listed as Discontinued in Drugs@FDA, no generic exists, and US commercial sales were discontinued in May 2023 with no confirmed relaunch — so it is approved but not currently marketed in the US.
How does Macimorelin work?
Macimorelin activates growth hormone secretagogue receptors in the pituitary and hypothalamus, the same receptors targeted by ghrelin, provoking release of growth hormone. Serum growth hormone is then measured at set intervals after the oral dose; a maximally stimulated level below the defined threshold supports a diagnosis of adult growth hormone deficiency.
Is Macimorelin FDA approved?
Yes. Macimorelin is approved by the U.S. FDA and has official prescribing information. Evidence level: approved labeling. Official prescribing information exists, based on clinical trials in people.
What is the half-life of Macimorelin?
Reported half-life: Mean terminal half-life of approximately 4.1 hours after a single oral dose in healthy subjects.
How is Macimorelin taken?
Oral solution, reconstituted from granules.
What side effects have been reported with Macimorelin?
Reported in the sources: Prolongs the corrected QT interval by roughly 11 msec; QT prolongation can lead to torsade de pointes ventricular tachycardia, and concomitant use with drugs known to prolong the QT interval, including certain antipsychotics, antiarrhythmics and antibiotics, is to be avoided; Diagnostic performance is weakest in the patients where testing is most ambiguous: in the combined intermediate and low likelihood groups of the pivotal study, positive agreement with the insulin tolerance test was 61 percent (lower 95 percent confidence bound 43 percent), 67 percent in the intermediate group and 33 percent in the low likelihood group. A negative macimorelin result does not reliably rule out growth hormone deficiency in these patients; Strong CYP3A4 inducers lower macimorelin concentrations and can cause a false positive test result; they must be stopped and allowed to wash out before testing; False negative results are possible in recent-onset hypothalamic disease, because deficiency caused by a hypothalamic lesion may not be detectable early in the disease process; repeat testing may be warranted; Commonly reported reactions include dysgeusia, dizziness, headache, fatigue, nausea, hunger, diarrhea, upper respiratory tract infection, feeling hot, hyperhidrosis, nasopharyngitis and sinus bradycardia; Safety and diagnostic performance have not been established in people with a body mass index above 40. Growth hormone therapy must be stopped at least one week before testing, other drugs affecting growth hormone secretion avoided, and deficient sex, thyroid and glucocorticoid hormones adequately replaced, or the test can mislead. This is a diagnostic agent with no approved therapeutic use; it is not indicated for raising growth hormone as a treatment.
Educational summary compiled from the sources listed above. Not medical advice. Peptide Vault does not sell, source or recommend any compound. Talk to a qualified clinician before starting or changing anything.