Bupropion-d9 hydrochloride is primarily used in research and analytical settings as a stable isotope-labeled internal standard. It aids in the accurate quantification and detection of bupropion and its metabolites in biological samples through techniques like mass spectrometry. This labeled compound ensures precision in pharmacokinetic studies, helping researchers understand drug metabolism, distribution, and elimination. It is also valuable in forensic and clinical toxicology to confirm the presence of bupropion in cases of overdose or compliance monitoring. Additionally, it supports the development and validation of analytical methods in pharmaceutical quality control.