Used as an internal standard in analytical chemistry, particularly in mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy, for accurate quantification of p-cresol in various samples. Its deuterated form enhances precision by minimizing interference with non-deuterated compounds. Applied in environmental studies to monitor p-cresol levels in water, soil, and air, ensuring compliance with safety regulations. Also utilized in biomedical research to study p-cresol's role as a uremic toxin in patients with kidney disease, aiding in the development of therapeutic strategies.