Participants in this double-blind, placebo-controlled study will receive 1 month of paroxetine and 1 month of placebo with the order of which is taken during the first month randomly assigned. Paroxetine will be administered at a daily dose of 10 mg for the first week and increased to a daily dose of 20 mg for the remainder of the study. After one month of medication, participants will abstain from smoking for one night and then undergo mental stress testing the following day. Immediately prior to the mental stress testing, participants will smoke a cigarette. Mental stressors will include speaking and math tasks. Physiological measures of stress (e.g., blood pressure, heart rate, and plasma catecholamine concentrations) and subjective measures of stress will be evaluated. Following the second month of medication, participants will again undergo the procedure for mental stress testing and evaluation.