Introduction Professional drivers’ knowledge about driving-impairing medications is not satisfactory. The aim of this study was to develop and test the reliability and validity of the questionnaires designed to measure the knowledge and attitude of professional drivers about the influence of various medications on driving ability. Methods The questionnaires for assessing professional driver’s knowledge (performance-based) and attitudes about influence of various medications on driving abilities were developed by creating the item pool, testing reliability and validity, and factor analysis. The study was conducted as a multicenter, cross-sectional study in Serbia and Bosnia and Herzegovina. The study population consisted of professional drivers, who filled out both questionnaires in three time intervals. Results Both questionnaires showed great internal consistency and temporal stability. Cronbach’s Alpha for the first questionnaire was 0.984 and for the second it was 0.944. The Kaiser–Meyer–Olkin test for the first questionnaire confirmed sampling adequacy with its value of 0.964 and for the second questionnaire it was 0.933. Exploratory factor analysis of the questionnaire showed that three factors were revealed after rotation for the first questionnaire and they explained 78.0% of variance. Both questionnaires showed high degree of correlation between scores after the first and repeated administration, Spearman’s rho coefficient of correlation for was 0.962 and 0.980. Conclusion Based on the results of this study, we believe that both questionnaires are useful tools for testing professional drivers’ knowledge and attitudes about the influence of medications on driving ability.

More knowledge about the impact of medication on driving are indicative of a lower likelihood of having a motor vehicle crash. The aim of this study was to investigate knowledge of professional drivers about the influence of driving impairing medicines in Serbia and Bosnia and Herzegovina. This multicenter cross-sectional study was conducted in 6 cities in Serbia and Bosnia and Herzegovina, during first trimester of 2017, with 221 professional drivers, using questionnaire with 35 statements, where participants expressed their agreement according to Likert scale, from completely disagree to completely agree. The average score related to the drivers’ knowledge was 131,58 (range from 49 to 175), 22,6% were unaware that some medicines may influence psychophysical abilities and ability to drive. A high percentage of participants in the study don’t know that a negative impact on the driving ability can be the result of the use of medicines from groups for which it is unexpected to have such effects, medicines that are dispensed without a medical prescription, herbal remedies, dietary supplements and medicines that affects eyesight or hearing. More than half didn’t know that medicines labeled with warning symbols Δ, ▲ and § are not allowed to be used immediately before or during driving. Professional drivers’ knowledge about driving impairing medicines is not satisfactory. Labeling system of these medicines is inadequate. These findings could help to identify drivers, who are at increased risk for using potentially impairing medicines, to inform and educate them, and to prevent driving under the influence of medicines.