In order for pharmacists to be collaboratively involved with patients in pharmacotherapy, there is a need to improve patients’ understanding of pharmacists’ involvement in extended pharmacotherapy, i.e., their interpersonal work. This study explores the factors that affect patients’ perceptions of pharmacists’ interpersonal work. A survey on patients’ perceptions of pharmacists’ interpersonal work was conducted among 450 patients aged 20 years or older who visited a pharmacy. Logistic regression analysis was performed with low and high patient perceptions of pharmacists’ interpersonal work as the objective variables. Valid responses were obtained from 350 participants. More than half of the respondents did not understand the nature of the interpersonal work of pharmacists. Patients who were unaware of pharmacists checking for side effects were more prevalent than those who were unaware of other interpersonal work. Explanations from the family pharmacist (OR＝2.25, P＝0.033) and trust in the pharmacist (OR＝1.11, P＝0.001) had a positive influence on patients’ perceptions of the pharmacist’s interpersonal tasks. As pharmacy pharmacists are increasingly becoming more involved with patients’ drug treatment and to ensure safe drug treatment practices for patients, it is considered important for pharmacists to actively explain their involvement in drug treatment to patients. This will be conducive to building trusting relationships, and for pharmacists to fulfil their function as family pharmacists.