Macimorelin Side Effects: What Studies Report

Macimorelin appears in the published literature almost entirely as a single-dose oral diagnostic agent for growth hormone (GH) deficiency rather than as a repeated-use therapeutic. That distinction shapes everything that can honestly be said about its side-effect profile: most safety observations come from studies in which participants received one oral dose during a timed stimulation test, with blood sampling over a few hours. This page summarises what those publications reported, and states plainly where the literature is silent. It does not tell anyone what to do.

This page is for educational purposes only and is not medical advice; consult a licensed physician for any question about diagnosis, testing, medication, or symptoms.

What the literature describes macimorelin as

A 2013 validation study in The Journal of Clinical Endocrinology and Metabolism described the macimorelin (AEZS-130)-stimulated growth hormone test as a novel oral stimulation test for the diagnosis of adult GH deficiency (PMID 23559086). In that validation work researchers administered macimorelin as a single oral dose of 0.5 mg/kg and measured stimulated growth hormone concentrations in adults being evaluated for GH deficiency (PMID 23559086).

Reviews of GH-deficiency diagnosis have placed macimorelin alongside other provocative tests: a 2018 update on the diagnosis of growth hormone deficiency discussed oral macimorelin as a stimulation-test option in the diagnostic landscape (PMID 32309600), and a review of current aspects of diagnosis and treatment of adult GH deficiency covered the diagnostic testing options available to clinicians (PMID 32202742). A 2024 review revisiting the glucagon stimulation test for adult GH deficiency is a useful reminder that each stimulation test carries its own tolerability considerations, which is why comparative studies were undertaken at all (PMID 38461479).

Tolerability in Diagnostic Trials: What Studies Report

The pivotal comparison appeared in 2018, when researchers compared a single oral macimorelin dose of 0.5 mg/kg with the insulin tolerance test in adults with suspected GH deficiency and reported agreement between the two tests as the primary outcome (PMID 29860473). On the safety side, the study reported that macimorelin was well tolerated in the population studied, with adverse events characterised as mild and transient (PMID 29860473).

The earlier validation study similarly reported that the oral macimorelin test was well tolerated in the adults tested, which was part of the rationale for pursuing it as an alternative to tests requiring induced hypoglycaemia (PMID 23559086). It is worth noting what kind of safety data this is: observations gathered over a single test day, in a monitored clinical setting, in adults selected for a diagnostic workup.

Taste disturbance and other commonly noted events

A single-dose, randomised controlled study in healthy adults evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin and reported dysgeusia — a temporary distortion of taste — among the adverse events observed after oral administration (PMID 32325373). Because macimorelin was given as an oral preparation in that study, researchers reported taste-related complaints in the context of the oral route itself (PMID 32325373).

Beyond taste disturbance, the healthy-adult study reported that single oral doses of macimorelin were generally well tolerated and that pharmacodynamic endpoints centred on stimulated growth hormone concentrations rather than on symptomatic outcomes (PMID 32325373). No verified publication in this set reported a pattern of severe or treatment-limiting adverse events after a single diagnostic dose.

Cardiac Repolarisation and QT/QTc: What Studies Report

Cardiac repolarisation was not left to incidental observation. A dedicated thorough QT/QTc study evaluated the effect of macimorelin on cardiac safety parameters in healthy participants (PMID 32961034). The existence of that study is itself informative: researchers considered the QT/QTc interval important enough to warrant a purpose-built trial in healthy participants rather than relying on electrocardiograms collected during diagnostic testing (PMID 32961034).

Reviews written for clinicians have folded cardiac and practical considerations into discussion of how the oral test is conducted; a 2022 review of macimorelin acetate for the diagnosis of childhood-onset growth hormone deficiency discussed the test's tolerability and practical conduct (PMID 36694890). None of the verified publications in this set reported arrhythmic events or cardiac outcomes from repeated, non-diagnostic macimorelin administration in humans — that scenario simply was not studied.

Paediatric Data: What Studies Report

An open-label, group comparison, dose-escalation trial evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in children with suspected growth hormone deficiency (PMID 34438400). The study used escalating single oral doses and, per the publication, researchers reported that the doses studied were generally well tolerated in that paediatric population (PMID 34438400).

A review of macimorelin acetate in childhood-onset growth hormone deficiency summarised where paediatric evidence stood and why an oral test was considered attractive in younger patients (PMID 36694890). As with the adult work, the paediatric data describe single-dose exposure in a supervised diagnostic setting; they do not describe ongoing administration.

Beyond Diagnostic Use: What Studies Report

One publication moved outside diagnostics. A 2023 pilot clinical trial assessed the safety and efficacy of macimorelin in patients with cancer cachexia (PMID 36860137). Researchers framed that work as a pilot, meaning the sample was small and the findings exploratory rather than confirmatory (PMID 36860137). A pilot trial in a medically complex population is not a substitute for long-term safety data, and the publication did not present itself as one.

For contrast, treatment-side literature on growth hormone itself is a separate body of work: a 2026 review of growth hormone replacement therapy in adults addressed replacement therapy rather than diagnostic stimulation testing (PMID 41912009). Conflating the safety profile of long-term hormone replacement with that of a single diagnostic dose of a ghrelin receptor agonist would misread both literatures.

Study-by-study summary

Why "well tolerated" is a narrow claim here

Three limits are worth stating explicitly. First, exposure duration: the adult diagnostic studies reported outcomes after a single oral dose given on one test day (PMID 29860473), so they cannot speak to cumulative or repeated exposure. Second, setting: participants were monitored during a structured stimulation test with timed blood sampling, as described in the validation literature (PMID 23559086). Third, population: participants were adults or children undergoing evaluation for pituitary disease, or healthy volunteers enrolled in pharmacology studies (PMID 32325373), not people using a compound outside medical supervision.

Reviews of GH-deficiency diagnosis have also emphasised that test interpretation depends on the clinical context, body composition, and the cut-offs applied — factors that sit alongside tolerability when a test is chosen (PMID 32309600), and a review of adult GH deficiency likewise addressed diagnosis and treatment as a combined clinical decision (PMID 32202742).

What This Literature Does Not Establish

• Repeated or long-term dosing in humans. Outside the small cancer cachexia pilot (PMID 36860137), the verified publications describe single-dose diagnostic exposure only; a long-term human safety profile is absent from this literature.
• Non-medical or performance-related use. No verified publication in this set examined macimorelin for body composition, athletic, cosmetic, or anti-ageing purposes, so no side-effect profile exists for those contexts.
• Hard cardiac outcomes. A dedicated study examined cardiac safety parameters in healthy participants (PMID 32961034); clinical arrhythmia outcomes over prolonged exposure were not addressed in these papers.
• Comparative tolerability rankings. The 2018 trial compared macimorelin with the insulin tolerance test for diagnostic agreement (PMID 29860473), while the glucagon stimulation test has been reviewed separately (PMID 38461479); this page does not rank tests against one another.
• Interactions and contraindications in individuals. Product labelling and prescribing decisions belong to regulators and clinicians, not to an educational summary.

Where this page sits within PeptideU's material

This page is limited to what published studies reported about adverse events, tolerability, and safety evaluation. The PeptideU course at /learn/macimorelin/ covers the separate teaching material — how the ghrelin receptor pathway works, how stimulation testing was designed and validated, and how researchers interpreted growth hormone responses. Readers looking for mechanism and test methodology will find that there; readers looking for reported safety observations have them summarised above. Anyone with a clinical question about macimorelin, growth hormone testing, or pituitary symptoms should raise it with a licensed physician.

References

• Macimorelin (AEZS-130)-stimulated growth hormone (GH) test: validation of a novel oral stimulation test for the diagnosis of adult GH deficiency (The Journal of Clinical Endocrinology and Metabolism, 2013)
• Macimorelin as a Diagnostic Test for Adult GH Deficiency (The Journal of Clinical Endocrinology and Metabolism, 2018)
• An update on the diagnosis of growth hormone deficiency (Discoveries, 2018)
• Current aspects of diagnosis and treatment of adult GH-deficiency (Problemy Endokrinologii, 2019)
• Safety, tolerability, pharmacokinetics, and pharmacodynamics of macimorelin in healthy adults: Results of a single-dose, randomized controlled study (Growth Hormone & IGF Research, 2020)
• Thorough QT/QTc Study Evaluating the Effect of Macimorelin on Cardiac Safety Parameters in Healthy Participants (Clinical Pharmacology in Drug Development, 2021)
• Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of Macimorelin in Children with Suspected Growth Hormone Deficiency: An Open-Label, Group Comparison, Dose-Escalation Trial (Hormone Research in Paediatrics, 2021)
• Macimorelin Acetate for the Diagnosis of Childhood-onset Growth Hormone Deficiency (TouchREVIEWS in Endocrinology, 2022)
• Pilot clinical trial of macimorelin to assess safety and efficacy in patients with cancer cachexia (Journal of Cachexia, Sarcopenia and Muscle, 2023)
• Once upon a time: the glucagon stimulation test in diagnosing adult GH deficiency (Journal of Endocrinological Investigation, 2024)
• Facts and news about growth hormone replacement therapy in adults (Annales d'Endocrinologie, 2026)