A new study has found that smokers who take multivitamins offset their healthy behaviour by smoking more cigarettes. This is an example of what psychologists call the licensing effect, which occurs when people make a virtuous choice that permits them to make a poor choice later on, such as when someone ‘earns’ a weekend binge by avoiding alcohol all week. In this case, smokers take multivitamins, a healthy choice that they believe reduces the risk of cancer and allows them to smoke more. In fact, there is no evidence that multivitamins protect against cancer.