Last reviewed 2026-04-23 · How we verify

MK0557

MK0557 is a ghrelin receptor (GHS-R1a) antagonist that blocks the orexigenic signaling of ghrelin to reduce appetite and food intake.

MK0557 is a ghrelin receptor (GHS-R1a) antagonist that blocks the orexigenic signaling of ghrelin to reduce appetite and food intake. Used for Obesity or overweight with weight-related comorbidities.

At a glance

Mechanism of action

Ghrelin is an endogenous hormone that stimulates hunger and appetite through the growth hormone secretagogue receptor 1a (GHS-R1a). By antagonizing this receptor, MK0557 suppresses the hunger signal, leading to reduced caloric intake and potential weight loss. This mechanism targets a distinct pathway from monoamine-based or GLP-1-based weight loss agents.

Approved indications

• Obesity or overweight with weight-related comorbidities

Common side effects

• Nausea
• Vomiting
• Diarrhea
• Headache

Key clinical trials

• A 2-Year Study of an Investigational Drug in Obese Patients (0557-011) (PHASE3)
• Efficacy of MK0557 in Combination With Sibutramine or Orlistat (0557-015)(COMPLETED) (PHASE2)
• A Study to Determine the Effects of MK0557 in Obese Subjects (0557-006)(COMPLETED) (PHASE2)
• MK0557 for the Treatment of Cognitive Impairment in Patients With Schizophrenia (0557-027) (PHASE2)
• A 1-Year Study of an Investigational Drug in Obese Patients (0557-012)(COMPLETED) (PHASE3)

Primary sources

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