Abstract Background: The use of drugs with fiscalized substances without a correct prescription and without ambulatory pharmacy services can have negative consequences for public health. Objectives : To evaluate the effectiveness of a continuing education program in drugstores and pharmacies that improves pharmacy staff competencies to provide ambulatory pharmacy services. Setting : Ambulatory retail establishments (drugstores and pharmacies) in Colombia. Method : A multicenter, prospective, parallel-group, cluster-randomized, controlled clinical trial was conducted. The intervention group (IG) received a continuing education program for 12 months, including web-based social networking sites with a virtual classroom, a virtual course composed of 7 modules, access to a drug and dispensing information system, and pharmacy staff training. Control group (CG) received written material on the correct use of complex dosage forms for 12 months. Main outcome measure: Pharmacy staff competencies (knowledge, skills, and attitudes). Results : The sample was 305 drugstores and pharmacies, 153 in the IG and 152 in the CG. Of the 750-pharmacy staff invited, 88% (659) agreed to participate; a total of 379 pharmacy staff were assigned to the IG and 280 to the CG. Of a total, 65.3% (430) were women with a mean age was 35.6 years. At the end of the study, in the IG was statistically significant differences (p<0.05) in the 25 skills and attitudes self-reported, also knowledge improved in six of the seven assessed modules. Conclusion : Providing a continuing education program using various educational and active participation strategies improves assessed knowledge and self-reported for the provision of ambulatory pharmacy services.