In this paper we study whether quitting smoking has the unintended consequence of increasing weight. To that end, we construct a synthetic panel from the Behavioral Risk Factors Surveillance System, that allows us to control for time invariant unobservables. We also exploit the changes in tobacco excise taxes, beer taxes and regulations regarding tobacco use to instrument the potential endogeneity of the decision to give up smoking. Our estimates are very close to those issued in the ’90s by the US Department of Health, and indicate that a 10% decrease in the incidence of smoking leads to an average weight increase of 1 to 1.5 kilograms per person (or 2.2 to 3.3 pounds). In addition, we find evidence that the effect overshoots in the short run, although a significant part remains even after two years. This implies that the cost of reducing the incidence of smoking is larger than previously estimated, although the overall benefit for Society is still positive.