Marijuana use is on the increase in Australia, particularly among teenagers. Information dissemination is likely to become the main vehicle for minimizing the harms associated with marijuana use, so there is a clear need to develop informative and convincing communication strategies to target young (potential and incipient) marijuana users. However, the Federal Government’s “zero tolerance” approach to drug use is accompanied by anti-drug messages that may lack credibility with young people who already use, or have used, marijuana. Cognitive dissonance theory, as well as research with warning labels on other products such as cigarettes, suggests that young people who currently use marijuana (current users) will find the information about marijuana and the information about other drugs (with which they have no experience) less believable than will young people who have not used marijuana (non-users); and that young people who have tried marijuana but intentionally discontinued usage (trier-rejectors) will find both sets of messages more believable than either current users or never-users. This study finds that, for many of the messages tested, the hypotheses about relative believability are supported.