Macimorelin (Macrilen): Uses, Evidence, Side Effects

Key Takeaways

• Macimorelin (brand name Macrilen) is approved as a diagnostic test for adult growth hormone deficiency, not as a treatment.
• It works by activating growth hormone secretagogue receptors in the pituitary and hypothalamus to trigger GH release.
• Six registered trials include studies on GH stimulation testing, cachexia, and healthy volunteer response.
• Reported side effects in FDA safety data are limited and each documented only once, so no pattern stands out.
• Safety and diagnostic accuracy have not been established in patients with a BMI above 40 kg/m2.

What Macimorelin Is

Macimorelin is a growth hormone secretagogue receptor agonist. Rather than replacing a hormone directly, it prompts the body's own pituitary and hypothalamus to release growth hormone. This receptor activation forms the basis of its use as a diagnostic stimulation test rather than an ongoing therapy.

What Macimorelin Is Approved For

Macimorelin, sold as Macrilen, is indicated for diagnosing adult growth hormone deficiency (AGHD). Clinicians use it to see whether the pituitary responds appropriately after administration, which helps confirm or rule out AGHD. The label notes a limitation: safety and diagnostic performance have not been established in people with a BMI above 40 kg/m2. There is no boxed warning on the label.

What the Evidence Shows

Macimorelin has been studied across 6 registered clinical trials. A completed Phase 3 trial evaluated the oral compound as a growth hormone stimulation test, supporting its diagnostic use. A separate completed Phase 2 trial explored repeated dosing in patients with cancer cachexia, a use outside its approved diagnostic indication. Another completed study examined copeptin response after oral macimorelin in healthy volunteers.

Reported Side Effects

FDA Adverse Event Reporting System data list a small set of reactions tied to macimorelin, each recorded a single time: bradycardia, dizziness, dysgeusia, fatigue, feeling hot, fluid retention, flushing, and nausea. These figures reflect individual case reports submitted to a passive surveillance system, not confirmed incidence rates or established causation. The low, evenly distributed counts suggest no single reaction dominates the reported safety profile.