In the theoretical framework of dynamic motivational activation, this study reveals the dynamics of antimarijuana public service announcement (PSA) processing, especially the processing of co-occurring positive and negative content. It specifies the important role of endogenous feedback dynamics of the information processing system and teases them apart from exogenous message effects. As suggested by real-time psychophysiological responses (heart rate, skin conductance level, and facial electromyography), the copresence of positive and negative content is most attention eliciting and is not moderated by individuals' marijuana experience. Marijuana experience, however, increases attention to arousing content in the PSAs, increases smiling responses to positive content, and escalates arousal to the PSAs in general. Implications for designing and evaluating PSAs and health campaigns are discussed. (Contains 3 figures and 1 table.)