In the last decade, clinical mass spectrometry use cases are spreading rapidly. Therapeutic drug monitoring (TDM) is the practice of monitoring therapeutic efficacy and side effects when a patient is undergoing treatment. This is especially important in drug therapy regimes where there could be concerns about potentially toxic symptoms, drug interactions, or other serious issues. A/Prof Masamitsu Maekawa shares his extensive experience using clinical mass spectrometry for TDM usage in this talk at RED 2024.