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

Doctors evaluating adults for suspected growth hormone deficiency need a reliable diagnostic tool that does not require an invasive infusion protocol. Macimorelin, sold under the brand name Macrilen, is an oral option developed for exactly this purpose.

Key takeaways

• Macimorelin (Macrilen) is approved to help diagnose adult growth hormone deficiency (AGHD), not to treat it.
• It works by activating growth hormone secretagogue receptors in the pituitary and hypothalamus.
• Safety and diagnostic performance have not been established in people with a BMI above 40 kg/m2.
• Six registered trials include a Phase 3 study that validated its use as an AGHD diagnostic test.
• Reported side effects in available data include dizziness, dysgeteusia, fatigue, flushing, and nausea, each noted once.

What Macimorelin Is

Macimorelin belongs to a drug class called growth hormone secretagogue receptor agonists. It prompts the pituitary and hypothalamus to release growth hormone by binding to these receptors, similar to the way the natural hormone ghrelin acts on the body. This receptor activation produces a measurable GH response that clinicians can use for diagnostic testing rather than for direct treatment.

What Macimorelin Is Approved For

Macrilen is indicated for diagnosing adult growth hormone deficiency. The test measures how the body responds after receptor stimulation, helping distinguish patients with AGHD from those with normal GH function. The label notes a limitation of use: safety and diagnostic performance have not been established in adults with a BMI over 40 kg/m2. No boxed warning is present on the label.

What the Evidence Shows

Six trials involving macimorelin are registered. Among the sample available, a Phase 3 study, "Validation of Macimorelin as a Test for Adult Growth Hormone Deficiency," was completed and supported its diagnostic role. An earlier Phase 1 trial in healthy subjects examined the compound as an oral ghrelin agonist, and a separate study without a designated phase looked at copeptin response after oral macimorelin in healthy volunteers.

Reported Side Effects

Reported reactions associated with macimorelin span several categories, including bradycardia, dizziness, dysgeusia, fatigue, feeling hot, fluid retention, flushing, and nausea. Each of these terms appears in available reports a single time. These figures reflect report counts submitted to a safety database, not confirmed incidence or proof that macimorelin caused the reaction.