Study objective: To assess cardiovascular conditions and other side effects associated with the use of nicotine polacrilex (NP), 2 mg. Design: A multicentered randomized control trial of early intervention for the prevention of COPD. Setting: Ten university medical centers in the United States and Canada. Participants: Adult smoking volunteers with evidence of early COPD; 3,923 in intervention and 1,964 controls. Intervention: Smoking cessation program, including NP. Measurements: Data on hospitalizations were collected annually. Data on reported NP side effects were collected at 4- month intervals for intervention participants. Results: The rates of hospitalization for cardiovascular conditions and cardiovascular deaths during the 5 years of the study were not related to use of NP, to dose of NP, or to concomitant use of NP and cigarettes. About 25% of NP users reported at least one side effect, but most were very minor and transient. Side effects associated with discontinuance of NP in 5% or more of users included headache, indigestion, mouth irritation, mouth ulcers, and nausea. There was no evidence that concomitant use of NP and cigarettes was associated with elevated rates of reported side effects. Participants in the smoking cessation intervention who received intensive levels of instruction and monitoring of NP use (initially at 12 meetings during 3 months) appeared to report significantly lower rates of side effects (dizziness, headache, and throat irritation) than control participants, presumed to have less instruction and monitoring. Conclusions: NP, as used in the Lung Health Study, appears to be safe and unrelated to any cardiovascular illnesses or other serious side effects.