BackgroundIn recent years, cancer chemotherapy is being conducted at outpatient clinics, wherein pharmacists are involved with patient guidance and management of adverse events as experts in medication therapy. Therefore, we clarified the influence of interventions by pharmacists during counseling of patients with cancer on patients’ quality of life.MethodsTo determine this influence, we conducted a survey to assess the quality of life of 39 patients with breast cancer who underwent their initial course of outpatient cancer chemotherapy at Gifu Municipal Hospital. A quality of life survey was conducted before the 1st, 2nd, and 3rd courses of treatment and was based on a method obtained from a survey paper entitled, “Quality of Life Questionnaire for Cancer Patients Treated with Anticancer Drugs.”ResultsTwenty patients were assigned to the intervention group, which received pharmacist counseling, and nineteen patients were assigned to the non-intervention group, which received no pharmacist counseling. Both groups were compared immediately before the 1st course and 2nd course. Regarding the subscale of social relationships, a significant difference was observed for malaise (p = 0.043), with the non-intervention group experiencing them to a greater degree than the intervention group. Regarding the change between immediately before the 1st course and the 3rd course, a significant difference was observed in the subscale of social relationships for nausea (p = 0.017), with the non-intervention group experiencing it to a greater degree than the intervention group.ConclusionsThe results suggest that receiving pharmacists’ guidance on adverse events and individually adjusted prescriptions tailored to address the occurrence of adverse events improved the treatment environment and enhanced the quality of life in the intervention group. These findings are beneficial in maintaining patients’ quality of life during cancer treatment.Trial registrationNo. UMIN000027171, Registration date: Apr 27, 2017. Retrospectively registered.