OBJECTIVES: Patients new to therapy for chronic conditions often have poor medication adherence that can lead to adverse outcomes and higher medical costs. Previous studies have demonstrated the benefit of pharmacist interventions to improve adherence. The objective of this study is to evaluate the impact of a community pharmacist telephone call program on medication adherence in patients new to therapy for any of nine therapeutics classes. METHODS: This prospective randomized trial used claims data from a large pharmacy chain beginning in February 2013. Patients were randomly assigned to an intervention group that received pharmacist phone calls to discuss their newly prescribed medication within three days after dispensing (n=219,611) or a control group that received no calls (n=225,497). We tracked patients’ claims data for 180 days to evaluate their medication adherence. Baseline demographic characteristics and therapeutic class distribution were compared between groups. Medication adherence was measured by Patient Days on Therapy (PDOT) within 180 days for every targeted therapeutic class (anti-anginal agents, betablockers, diuretics, anti-asthmatic and bronchodilator agents, genitourinary agents, anti-depressants, anti-Parkinson, anti-coagulants, and hematological agents) and overall. Significance was determined using ' and t tests between intervention and control groups. RESULTS: Both intervention and control groups had similar baseline demographic and therapeutic class distributions (P>0.05). Comparison by therapeutic class found large variations of adherence with hematological agents having the greatest adherence (PDOT=105.57) while anti-angina agents had the lowest (PDOT=47.06). The intervention group had greater adherence than the control group in every therapeutic class with the PDOT differences ranging from 0.48 days for anti-angina agents to 2.63 days for anti-Parkinson agents (P≤