Doxylamine D5 succinate is primarily used in research and analytical applications as a labeled internal standard in mass spectrometry. It aids in the accurate quantification and identification of doxylamine in various biological samples, such as blood, urine, or plasma. This labeled compound is essential for ensuring precision in pharmacokinetic studies, drug metabolism research, and forensic toxicology analyses. Its deuterated structure allows for clear differentiation from the non-labeled form, enhancing the reliability of analytical results.