The first aim of this research was to assess the effectiveness, in terms of emotional and behavioral reactions, of moderately vs. highly TVWs (Threatening Visual Warnings) displayed on tobacco packs. Given the key role that emotional reactions play in explaining the effect of TVWs on behaviors, psychophysiological and self-report methods were used–for the first time in this context–to measure the emotions provoked by TVWs. The second aim of this research was to determine whether increasing the size of warnings, and their display on plain packaging (compared with branded packaging) would improve their effectiveness.A within-subjects experiment was conducted. Three variables were manipulated: health warning threat level (high vs. moderate), image size (40% vs. 75%) and pack type (plain vs. branded). A convenience sample of 48 French daily smokers participated. They were exposed to eight different packs of cigarettes in a research lab at the University of Rennes. Smokers’ emotions and behavioral intentions were recorded through self-reports. Emotions were also evaluated using psychophysiological measurements: electrodermal activity and facial electromyography. The results revealed that TVWs with a high threat level are the most effective in increasing negative emotions (fear, disgust, valence, arousal) and behavioral intentions conducive to public health (desire to quit, etc.). They also highlight the appeal of increasing the size of the warnings and displaying them on plain packs, because this influences emotions, which is the first step toward behavioral change.Increasing the threat level of TVWs from moderate to high seems beneficial for public health. Our results also confirm the relevance of recent governmental decisions to adopt plain packaging and larger TVWs (in the UK, France, Ireland, Canada, New Zealand, Hungary, etc.).