Media are important. Especially the media we trust. One might express the effect of a piece of journalism (J) about, say, a particular drug or food, as a factor of media authority (A), multiplied by the size of audience (D), divided by the availability of credible alternative sources (S).
The more of the latter which are accessible to the audience, and thus the greater the challenge to the “truthiness” of (J), the lesser the impact on individual and collective behavior. Where people trust the news source, and the issue is complex, and alternative analyses are not easily sourced, the effect is greater.