In 2013, we prescribed daiuzusen for 3 patients with intractable pain; pain from complex regional pain syndrome, colic pain of unknown origin after an abdominal operation, and colic pain from advanced colon cancer and ileus. A dose of daiuzusen (containing uzu 0.5-2 g) quickly relieved their pain in several minutes. Another common symptom was “cold” in their bowel or extremities when they were feeling pain. Aconite levels in drugs and patients' serum after taking daiuzusen were analyzed by liquid chromatography tandem mass spectrometry. Daiuzusen per 1 g of uzu contained aconitine 1.28 μg, mesaconitine 2.31 μg, and hypaconitine 92.89 μg, while jesaconitine was not detected; this was about 5 to 35 times the level of tsumyakushigyakuto per 1 g of uzu. Serum concentrations of hypaconitine peaked in the study at 1.11 ng/mL after about an hour of taking daiuzusen (1 g of uzu). We posit that the immediate effect after taking daiuzusen was due to transmucosal absorption of uzu components. However serum hypaconitine, which we are now able to monitor, is at least one practical way of indicating the use of uzu or bushi containing prescriptions.