Cannabis (marijuana) use is on the increase in many countries, particularly among teenagers. Information dissemination is likely to become the main vehicle for minimising the harms associated with cannabis use. Thus there is a clear need to develop informative and convincing communication strategies to target young (potential and incipient) cannabis users. Cognitive dissonance theory, as well as research with warning labels on other products, suggests that young people who currently use cannabis will find the information about cannabis and the infonnation about other drugs (with which they have no experience) less believable than will non-users. This study finds support for the hypothesis regarding cannabis and cocaine, though not heroin.