This review evaluates the effectiveness of health warning messages on tobacco packages. The evidence suggests that the impact of health warnings depends on their size and design. Obvious text-only warnings have little impact, while prominent health warnings on the front of packages serve as a prominent source of health information for smokers and non-smokers, increase health knowledge and perceptions of risk, and promote smoking cessation. Comprehensive warnings are effective among youth and may help prevent smoking initiation. Pictorial health warnings that elicit strong emotional reactions are significantly more effective. Health warnings on tobacco packages are among the most direct and prominent means of communicating with smokers. Larger warnings with pictures are significantly more effective than smaller, text-only messages. The review found that health warnings are effective in promoting smoking cessation and discouraging youth initiation. They also increase the use of effective cessation services. Health warnings have been associated with increased use of effective cessation services, as shown by increased call volumes to smoking cessation helplines in several countries after health warnings were implemented. Health warnings have also been associated with increased long-term abstinence from smoking. Surveys among former smokers suggest that health warnings promote long-term abstinence from smoking. In Australia, 62% of quitters reported that pictorial warnings had helped them to give up smoking, while 75% reported the warnings had an effect on their behaviour. In the EU, approximately 30% of former smokers reported that health warnings had helped prevent them from smoking again. Health warnings have been found to be effective in discouraging smoking initiation among youth. Population-based surveys indicate that significant proportions of youth non-smokers report that warnings have discouraged them from smoking. Longitudinal surveys in Australia found that experimental and established smokers were more likely to think about quitting and forgo cigarettes after the implementation of large pictorial warnings. The content and theme of health warnings also play a role in their effectiveness. Graphic depictions of disease appear to be the most reliable way to elicit negative emotional reactions to health warnings. Warnings that highlight negative aesthetic effects of smoking may be particularly effective among young people. Warnings that depict elements of human suffering have also been found to be effective. The use of 'narratives' or personal testimonials has been associated with increased emotional impact of warnings. Positive-themed cessation messages are typically rated as having lower impact than fear-appeals or 'graphic' health warnings. However, smokers consistently endorse the inclusion of detailed information on the benefits of quitting, as well as concrete information on forms of cessation assistance and tips for quitting. Potential adverse outcomes from health warnings include increased smoking as an act of defiance. However, the evidence suggests that graphic, fear-arousing warnings are generally effective in promoting smoking cessation and discouraging youth initiation. The effectiveness of health warnings may vary depending on the population and the design of the warnings. Larger pictorial warnings are generally more effective than smaller, text-only messages. The review also highlights the importance of cultural appropriateness and the need for furtherThis review evaluates the effectiveness of health warning messages on tobacco packages. The evidence suggests that the impact of health warnings depends on their size and design. Obvious text-only warnings have little impact, while prominent health warnings on the front of packages serve as a prominent source of health information for smokers and non-smokers, increase health knowledge and perceptions of risk, and promote smoking cessation. Comprehensive warnings are effective among youth and may help prevent smoking initiation. Pictorial health warnings that elicit strong emotional reactions are significantly more effective. Health warnings on tobacco packages are among the most direct and prominent means of communicating with smokers. Larger warnings with pictures are significantly more effective than smaller, text-only messages. The review found that health warnings are effective in promoting smoking cessation and discouraging youth initiation. They also increase the use of effective cessation services. Health warnings have been associated with increased use of effective cessation services, as shown by increased call volumes to smoking cessation helplines in several countries after health warnings were implemented. Health warnings have also been associated with increased long-term abstinence from smoking. Surveys among former smokers suggest that health warnings promote long-term abstinence from smoking. In Australia, 62% of quitters reported that pictorial warnings had helped them to give up smoking, while 75% reported the warnings had an effect on their behaviour. In the EU, approximately 30% of former smokers reported that health warnings had helped prevent them from smoking again. Health warnings have been found to be effective in discouraging smoking initiation among youth. Population-based surveys indicate that significant proportions of youth non-smokers report that warnings have discouraged them from smoking. Longitudinal surveys in Australia found that experimental and established smokers were more likely to think about quitting and forgo cigarettes after the implementation of large pictorial warnings. The content and theme of health warnings also play a role in their effectiveness. Graphic depictions of disease appear to be the most reliable way to elicit negative emotional reactions to health warnings. Warnings that highlight negative aesthetic effects of smoking may be particularly effective among young people. Warnings that depict elements of human suffering have also been found to be effective. The use of 'narratives' or personal testimonials has been associated with increased emotional impact of warnings. Positive-themed cessation messages are typically rated as having lower impact than fear-appeals or 'graphic' health warnings. However, smokers consistently endorse the inclusion of detailed information on the benefits of quitting, as well as concrete information on forms of cessation assistance and tips for quitting. Potential adverse outcomes from health warnings include increased smoking as an act of defiance. However, the evidence suggests that graphic, fear-arousing warnings are generally effective in promoting smoking cessation and discouraging youth initiation. The effectiveness of health warnings may vary depending on the population and the design of the warnings. Larger pictorial warnings are generally more effective than smaller, text-only messages. The review also highlights the importance of cultural appropriateness and the need for further