Abstract Glycerol phenylbutyrate (GPB) is an ammonia scavenger drug commonly used in the therapy of patients with urea cycle defects. Reported side effects include body odor, abdominal pain, nausea, burning sensation in mouth, vomiting, and heartburn. We report on a 3‐year‐old late diagnosed female patient with ornithine transcarbamylase deficiency that experienced severe loss of appetite under treatment with GBP. Due to catabolism (calory intake about 400 kcal/day) and the associated risk of metabolic decompensation, GBP treatment was discontinued. Her appetite and eating behavior normalized within 1 day after discontinuation of GBP and switch to sodium benzoate. Our case demonstrates that GBP can cause severe loss of appetite that may put patients at risk of metabolic decompensation and require discontinuation of therapy.
