Sample Size Calculation
The baseline estimates were obtained from The Real World Data database (Health, Clinic, Education, Information Evaluation Institute/Real World Data, Co, Ltd), which includes approximately 19 million patients’ data from 170 institutions in Japan. According to this database, of 1464 patients who were prescribed lithium carbonate in a 6-month period up to June 1, 2018, therapeutic serum lithium levels (between 0.4 mEq/L and 1.0 mEq/L) were maintained in 818 (55.9%) patients. In this trial, we estimated that a total of 108 patients would provide 80% power if 48 (80%) patients in the reminder group and 33 (55%) patients in the usual care group achieved the primary outcome using the 2-sided chi-square test with a 2-side alpha level of .05. Assuming a dropout rate of 10%, the final sample size was set at 120.