What is the medical professional liability cost associated with preventable adverse drug effects? Harmful medication errors, or preventable adverse drug events (ADEs), are a prominent quality and cost issue in healthcare. Injectable medications are important therapeutic agents, but they are associated with a greater potential for serious harm than oral medications. The economic burden of preventable ADEs associated with inpatient injectable medications and the associated medical professional liability (MPL) costs had not been previously described in the literature.This study finds that the healthcare and MPL costs associated with preventable ADEs are substantial: The authors estimate that inpatient preventable ADEs associated with injectable medications increase the annual US payer costs by $2.7 billion to $5.1 billion, while MPL costs associated with injectable medications total $300 million to $610 million annually.