Plain packaging significantly reduced the probability of perceiving the stimulus cigarettes as less harmful in comparison to the current package design (OR 0.398, 95% CI 0.333 to 0.476, p<0.001) and the modified package design (OR 0.729, 95% CI 0.626 to 0.849, p<0.001). Plain packaging enhanced the perceived risk of cigarette products even in a highly regulated setting such as Uruguay. Both the elimination of distinctive brand elements and the use of Australia’s dark brown background colour contributed to the observed effect.