Introduction: Food-drug can have a significant influence on the therapeutic success of the drug and on the adverse effect profiles of many drugs being administered. This study assessed the prevalence of potential drug-food interactions and orientation of health professionals on the proper use of medicines. Methods: Cross-sectional study which included 517 patients aged 18 years or over between May-August 2012. The analysis of the information included estimates of central tendency, variability and proportions. Multivariable analysis was performed by the Statistical Learning Theory Exhaustive CHAID algorithm was used to define of cut-offs for the complexity of pharmacotherapy and prioritize patients more likely to take their medications incorrectly with regard to food. Results: 1786 drugs were used by patients. Captopril and omeprazole were the most incorrectly used. Total of 66.0% of patients reported that they had not received any information on their pharmacotherapy and 95.2% stated that they had doubts or difficulties that could have been resolved by the pharmacist. An absence of additional information to those strictly necessary for compliance with the regimen of drugs prevailed (89.7%). The most common inaccuracy was taking a drug with food that should be taken on an empty stomach to improve absorption of the drug (57.7%). Conclusion: Professionals, in general, do not seem to warn their patients to take their medications on a full or empty stomach, at least in writing medications. Health professional awareness of the drug administration process can reduce medication errors and may contribute to the optimization of pharmacotherapy.