OBJECTIVE: To determine pharmacist's interventions led to change in overall drug cost and to describe the characteristics of pharmacist's interventions in a Thai intensive care unit. METHODS: A Prospective, standard care-controlled study design was used to compare overall drug costs of patients receiving care form patient care team including a clinical pharmacist with standard care (no pharmacist on team).  All Patients admitted to the medical intensive care unit (ICU) 1 and 2 during the same period were included in the study. The outcome measures were overall drug cost and length of ICU stay. Interventions made by the pharmacist in the study group were documented. The analyses of rate of acceptance and cost saving and/or cost avoidance were also performed. RESULTS: A total of 65 patients were admitted to either ICU 1 or 2 during the 5 week- study period. The pharmacist participated in patient care and made total of 127 interventions for the ICU-1 team. Ninety-eight percent of the interventions were accepted by physicians. The difference of overall drug cost per patient between two groups was 6,982.05 THB (41,298.5 THB in study group and 48,271.55 THB in control group, p = 0.138). The average length of ICU stay for the intervention group and the control group was not significantly different (7.16 days VS 6.18 days, p=0.995). The 125 accepted interventions were evaluated for cost saving and cost avoidance. Pharmacist's interventions yielded a total of 75,624 THB from drug cost saving and 11,301 THB from adverse drug event cost avoidance. The net cost saved and avoided from pharmacist interventions was 86,925.81 THB. Interventions involving antibiotic use accounted for the largest economic impact (75,132.18 THB). CONCLUSION: Having a pharmacist participated in ICU patient care team can reduced overall drug cost, cost saving, and cost avoidance. The largest economic impact involved antibiotic use.