Background Distractor efficiency of multiple choice item responses is a component of item analysis used by the examiners to to evaluate the credibility and functionality of the distractors.Objective To evaluate the impact of functionality (efficiency) of the distractors on difficulty and discrimination indices.Methods A cross-sectional study in which standard item analysis of an 80-item test consisted of A type MCQs was performed. Correlation and significance of variance among Difficulty index (DIF), discrimination index (DI), and distractor Efficiency (DE) were measured.Results There is a significant moderate positive correlation between difficulty index and distractor efficiency, which means there is a tendency for high difficulty index go with high distractor efficiency (and vice versa). A weak positive correlation between distractor efficiency and discrimination index.Conclusions Non-functional distractor can reduce discrimination power of multiple choice questions. More training and effort for construction of plausible options of MCQ items is essential for the validity and reliability of the tests.