Docetaxel-d9 is primarily used in research and development as an internal standard in analytical chemistry. Its deuterated form allows for precise and accurate quantification of docetaxel in biological samples using techniques like liquid chromatography-mass spectrometry (LC-MS). This is particularly valuable in pharmacokinetic studies, where understanding the absorption, distribution, metabolism, and excretion of docetaxel is critical. Additionally, it aids in the development and validation of analytical methods for therapeutic drug monitoring, ensuring patients receive optimal dosages during cancer treatment. Its stability and isotopic labeling make it a reliable tool for reducing variability and improving the accuracy of experimental data.