First Comes Substance Use, Then Comes Social Media Posts? Examining the Temporal Ordering and Relative Strength of Relations Across Alcohol, Tobacco and Marijuana Use and Posting Behavior.

Social media posts represent a major route by which youth share their substance use cognitions and experiences with others. Extant research has primarily examined relations between alcohol-related posts and posters' own alcohol use, yet little is known about the role of social media in the use of less socially accepted substances, namely tobacco and marijuana. Our study represents the first to examine the relative strength of this relation across alcohol, tobacco, and marijuana. The current research used a one-month time lag to tease apart the temporal ordering of substance-use-posting and participants' own substance use. A sample of 282 15-20-year-olds (Mage = 18.4, SD = 1.3, 52.9% female) in the United States completed two self-report surveys, one month apart. Results of a cross-lagged panel model revealed significant effects of alcohol and marijuana consumption on subsequent alcohol- and marijuana-related posting, respectively (i.e., selection effects). However, reverse relations (i.e., self-effects) were not significant. Further, we found no differences in the strength of selection effects across substances, suggesting they are similar for both more (alcohol) and less (marijuana and tobacco) socially acceptable substances. Results point to the importance of using young people's social media posts as a way to help identify individuals at risk for heightened substance use and social media as a mechanism for targeted prevention programming.