Community pharmacists play a vital role in delivering person-oriented services, such as addressing prescription inquiries, providing home care services, and conducting medication follow-ups. Despite their significance, no nationwide surveys have assessed the efficacy of these pharmaceutical activities. Therefore, this study aimed to collect information on these three pharmacist tasks and investigate their effectiveness in preventing serious adverse drug reactions and reducing medical costs. Ten percent of insurance pharmacies in each prefecture were randomly selected to participate in the survey. Data were collected on basic pharmacy information, prescription inquiries, home care services, and medication follow-up, which spanned from 12 June to 18 June 2023. Of the 561 pharmacies pre-registered for the study, valid responses were obtained from 433 pharmacies (77.2%). The reported cases included 3064 prescription inquiries, 765 home care services, and 326 medication follow-ups. Prescription inquiries prevented serious adverse drug reactions in 122 cases, home care services in 209 cases, and medication follow-ups in 13 cases. The cost reductions associated with these activities were ¥28291790, ¥58285600, and ¥2544950, respectively, resulting in a total cost reduction of ¥89122340. The annual cost reduction was ¥33229078321.7, assuming a severity rate of 6.7%. The estimated annual reduction in medical costs specifically attributed to prescription inquiries was ¥8732177830. This study indicates that pharmacists prevent adverse drug reactions and contribute to the safety of drug treatment through prescription inquiries, home care services, and medication follow-up. These tasks reduced annual medical costs by approximately ¥42 billion, highlighting the economic and healthcare benefits of community pharmacy services.