Macimorelin (Macrilen): Uses, Mechanism, and Side Effects

If a doctor has suggested testing for adult growth hormone deficiency, macimorelin may come up as part of that workup. Unlike therapies taken repeatedly, it is used as a single diagnostic test rather than an ongoing treatment.

Key takeaways

• Macimorelin (brand name Macrilen) is FDA-approved to help diagnose adult growth hormone deficiency (AGHD).
• It works by activating growth hormone secretagogue receptors in the pituitary and hypothalamus, prompting GH release.
• Safety and diagnostic performance have not been established in people with a BMI above 40 kg/m2.
• Six registered trials include studies in GH stimulation testing, cancer cachexia, and healthy volunteers.
• Reported side effects in available data include dizziness, nausea, fatigue, and flushing, each noted once.

What Macimorelin Is

Macimorelin is classified as a growth hormone secretagogue receptor agonist. It binds to receptors in the pituitary and hypothalamus that trigger the release of growth hormone. Because this response can be measured, the compound is used as a diagnostic tool rather than a daily medication.

What Macimorelin Is Approved For

Macimorelin, sold under the brand name Macrilen, is indicated for diagnosing adult growth hormone deficiency. It does not carry a boxed warning. The label notes a limitation of use: safety and diagnostic performance have not been established in patients with a BMI over 40 kg/m2.

What the Evidence Shows

Macimorelin has been studied across six registered clinical trials. A completed Phase 3 trial evaluated the oral compound, then known as AEZS-130, as a growth hormone stimulation test. A separate completed Phase 2 trial examined repeated dosing in patients with cancer cachexia, looking at safety and efficacy outside the diagnostic setting. Another study, without a specified phase, assessed copeptin response after oral macimorelin stimulation in healthy volunteers.

Reported Side Effects

Reported reactions associated with macimorelin include bradycardia, dizziness, dysgeusia, fatigue, feeling hot, fluid retention, flushing, and nausea, each logged a single time in available reports. These figures reflect raw report counts submitted to a safety surveillance system, not confirmed incidence or proven causation. The small number of reports is consistent with macimorelin's use as a one-time diagnostic test rather than a chronic therapy.