Objective This methodological study was performed to develop a Rational Use of Drugs Scale (RUDS). Design and samples After defining the scale items and taking expert opinion, 325 adults tested the internal consistency, structure, and criterion validity of the final scale. Measurements A literature review was used to generate the initial items. Evaluation by an expert panel established content validity for these items, and pilot testing of the draft tool was performed. Explanatory and confirmatory factor analyses were used to establish construct validity, and internal consistency and test-retest reliability were calculated. Results Using exploratory and confirmatory factor analyses, the RUDS was found to have a structure comprising 1 factor and 21 items, with a total scale variance of 31.99%. The RUDS assessed whether patients used effective, safe, appropriate, and inexpensive drugs. Cronbach's alpha coefficient was 0.84. Conclusion The RUDS might be a valid and reliable instrument for public health practitioners to assess knowledge, attitude, and behaviors related to drug use.