Project Summary/Abstract Addiction to ENDS products is a newly emerging form of nicotine addiction. Understanding the product characteristics and the harmful and potentially harmful constituents (HPHCs) that contribute to ENDS addiction is vital for effective FDA CTP regulation. This HPHC list, however, was last updated in 2012, just prior to the rise in ENDS popularity. Since two of the five addiction-related HPHCs are tobacco-related minor alkaloids (e.g., nornicotine), then it suggests research on ENDS-specific minor alkaloids is warranted. One uniquely prevalent minor alkaloid in ENDS is β-nicotyrine, which is formed by aging and/or aerosolizing e-liquids and can reach 25% of nicotine levels when vaped. Our pilot work found that β-nicotyrine approximately doubles the half-life of nicotine and that it functions as a nicotinic acetylcholine receptor (nAChR) agonist with functional efficacy at α4β2 nicotinic-AChRs similar to nornicotine. Given its a) abundance in ENDS aerosols, b) similarities to nornicotine, and c) ability to inhibit nicotine metabolism, β-nicotyrine may contribute to the addiction-relevant effects of ENDS and represent a novel HPHC. If we find β-nicotyrine has abuse liability or increases the abuse liability of nicotine, it suggests the CTP should consider it a HPHC given that the FDA considers other less prevalent minor alkaloids as HPHCs. The present project will initially characterize the pharmacokinetics of β- nicotyrine and its interaction with nicotine metabolism, and then subsequently determine its effects in FDA- recommended animal models of abuse liability, including drug discrimination, intracranial self-stimulation (ICSS) and drug self-administration. This project is innovative because: 1) it extends research on minor alkaloids, a class of constituents that includes HPHCs with established abuse liability, 2) it will be the first to examine the abuse liability of β-nicotyrine and its ability to alter the abuse liability of nicotine, including at vaping relevant concentrations, and 3) it will be the first to characterize the PK of β-nicotyrine and how it alters nicotine PK. In so doing, this project could elucidate novel mechanisms mediating ENDS addiction and test the proposed β- nicotyrine hypothesis.