O-Desmethyl Mebeverine acid D5 is primarily used as an internal standard in analytical chemistry for the quantification of mebeverine and its metabolites in biological samples. Its deuterated structure ensures accurate and precise measurements in mass spectrometry, minimizing interference from endogenous substances. This compound is crucial in pharmacokinetic studies, helping researchers understand the absorption, distribution, metabolism, and excretion of mebeverine in the body. It is also employed in clinical research to monitor therapeutic drug levels and ensure compliance in patients undergoing treatment for gastrointestinal disorders.