OBJECTIVES: In the development of an adverse drug reactions (ADRs) screener, ADRs were collated according to symptom clusters (SCs) to improve psychometric efficiency. The ADDRESS (Adverse Drug Reaction/Event Screening System) application is programmed in a manner such that, when multiple drugs are being screened, SCs that are duplicated across more than one drug are only asked once. This suggests a hypothesis that the number of SCs per drug will reduce as the number of drugs being screened for a given patient increases. Our objective is to understand the function of SC questions required by number of drugs being used by patients in a Medicaid population. METHODS: Using a Medicaid database from a previous study, we identified 4133 generic drug entities (drug differ by dosage form) in the dataset. The drugs in the Medicaid Database were matched with the ADDRESS database by generic name. Drugs were ignored if no match could be made. The association between the most common SCs clusters of the top 465 most prescribed drugs and the numbers of prescribed drugs per patient on Medicaid population are investigated and the maximum likelihood method is used to show the maximum number of SCs covered per patient per drug. RESULTS: There were 49.26 percent of drugs (n=2036) in the Medicaid database matched to ADDRESS database. The number of ADR SCs per drug per person taken follows an exponential distribution. If a patient is taking over 30 drugs, the number of ADR SCs per drug per individual would converge around 1. CONCLUSIONS: As the number of drugs in an individual’s therapy increases, SCs duplication increases to the point that ADR SCs exponentially decrease to around 1 new SC per additional drug per person in the Medicaid population examined.