Effects of Very Low Nicotine Content Cigarettes Among Adults Who Smoke Daily in South Korea

The goal of this clinical trial is to learn how switching to very low nicotine content (VLNC) cigarettes affects smoking behavior and nicotine exposure among adults in South Korea who smoke conventional cigarettes daily. The main questions it aims to answer are: * Do participants assigned to VLNC cigarettes smoke fewer cigarettes per day during the 7 days before the Week 14 endline visit than those assigned to normal nicotine content (NNC) cigarettes? * Do participants assigned to VLNC cigarettes have more smoke-free days during the 12-week randomized intervention period than those assigned to NNC cigarettes? Researchers will compare participants assigned to VLNC cigarettes with those assigned to NNC cigarettes to evaluate differences in smoking behavior, nicotine exposure, dependence, craving, withdrawal symptoms, abstinence-related outcomes, use of other tobacco or nicotine products, product perceptions, policy support, and behavioral patterns assessed using ecological momentary assessment. Participants will: * Complete a 1-week baseline period while continuing to smoke their usual-brand cigarettes. * Be randomly assigned to receive either VLNC or NNC SPECTRUM research cigarettes for 12 weeks. * Attend scheduled study visits and complete questionnaires, daily surveys, and ecological momentary assessments. * Provide urine samples for assessment of nicotine exposure and complete other study assessments related to smoking behavior and symptoms. Up to approximately 350 individuals may be recruited and screened to obtain approximately 300 randomized participants.