The objective of the study was to evaluate the therapeutic efficacy of nicotine nasal solution (NNS) for smoking cessation from the stopping day up to 3 months. We also followed the participants for 2 yrs after ceasing smoking to assess what happens after stopping using NNS. In a placebo-controlled, double-blind, 2 yr prospective study, 157 smokers were given either NNS, one dose containing 1 mg of nicotine per 100 microL (n=79), or placebo (n=78). Treatment was continued for up to 1 yr. One day after quitting smoking, the average number of daily doses was 11 in the group assigned NNS and 14 in the group assigned the placebo, and after 6 weeks, 14 and 6 doses, respectively, among abstinent participants still using spray. After 3 months, 65% of the abstainers in the nicotine group were still using the NNS. The abstinence rates were 51, 39 and 29% after 6 weeks, 3 and 6 months, respectively, as compared to 24, 19 and 18% in the placebo group (p=0.0003; p=0.003; p=0.050). The proportion abstinent at the 1 yr (25 vs 17%) and 2 yr follow-ups (19 vs 14%) was higher among those assigned to the nicotine than to the placebo group, but not significantly so for the numbers used in the study. In conclusion, the use of nicotine nasal spray significantly increased the abstinence rate during the first 6 months following the quitting day.