Electronic cigarettes (e-cigarettes) are the fastest growing harm reduction product. Many e-cigarette users obtain nicotine blood levels from e-cigarettes that are much higher than those from nicotine replacement products and, in some studies, similar to that for tobacco cigarette users. Given this, one would expect abrupt cessation of e-cigarettes to produce withdrawal symptoms but this has not been tested. We propose to recruit 120 long-term e- cigarette-only users. Participants will enter a within-participants study with random, balanced order of assignment to four conditions: a) their own e-cigarettes, b) a new nicotine e-cigarette, c) the non-nicotine (i.e. placebo) version of the new e-cigarette, and d) no use of any e-cigarettes. The use of nicotine or non-nicotine new e-cigarettes will be double-blind. Participants will be instructed to abstain from tobacco and nicotine products during the study. Each condition will last 5 days with a 2 day washout between conditions. To encourage compliance we will use an escalating payment system with bonuses that has resulted in high compliance rates in our prior studies. Participants will monitor symptoms of nicotine withdrawal daily via an Interactive Voice Response system. They will also attend 3 lab visits/week to provide carbon monoxide and cotinine samples to determine compliance payments, and to complete longer surveys, a cognitive task and a task to measure increased motivation to use e-cigarettes. We will test the effect of abstinence (own e-cigarette vs no e-cigarette) and its pharmacological specificity (new nicotine e-cigarette vs new non-nicotine e-cigarette). Our results will help determine a) the addiction potential of e-cigarettes, b) whether labeling should warn purchasers of e-cigarettes that abrupt cessation can induce withdrawal, and c) whether withdrawal problems should be included in risk/benefit assessments of e-cigarettes.