This study examined whether the number of psychotropic medications an individual is taking across classes influences side effects among adults with Intellectual Disability (ID). Participants were 80 adults diagnosed with ID. Dependent variables were the composite score and domain scores of the Matson Evaluation of Drug Side-effects (MEDS), which is an instrument used to assess side effects. There were three levels of the independent variable: Group 1 – those taking zero psychotropic medications, Group 2 – those taking one psychotropic medication, and Group 3 – those taking two psychotropic medications across different medication classes. There was a significant main effect regarding number of psychotropic medication classes prescribed. Further analysis revealed that four of the nine MEDS domains had significantly different mean scores for number of psychotropic medication classes. For the majority of MEDS domains, such as Central Nervous System-General, Parkinsonism/Dyskinesia, and Behavioral/Akathesia domains, participants in the no psychotropic medication group had significantly lower mean scores than those in the one and two psychotropic medication groups. Only two MEDS domains, Cardiovascular and Hematologic Effects as well as Skin, Allergies, and Temperature, were significantly different between participants taking one psychotropic medication as compared with two psychotropic medications from different classes. Implications of these findings and recommendations for future research are discussed.