The misuse of prescription drugs has become an epidemic in the United States and a number of other countries, with consequently enormous socioeconomic impact. The manufacturers of new molecular entities (NMEs) are responsible for evaluating the potential for their candidate drugs to be abused in the intended clinical population or diverted for non-medicinal use. Abuse liability is assessed both nonclinically, in vitro and in animal models, and in human clinical trials. Regulatory guidance has been provided by the FDA and EMA and provides a framework for the conduct of abuse liability assessments; importantly, the guidance does not distinguish between molecules based on therapeutic indication or molecule type (small versus large molecules). This webinar will provide an overview of the regulatory guidance on abuse liability assessment, explain why comprehensive assessments are important for all NMEs, and clarify the distinctions between small and large molecules that reduce the likelihood that large molecules will be abused.