How peers shape teen beliefs about marijuana and substance use

This study examined how beliefs about substance use—including marijuana—develop during early adolescence and how peer influence shapes these beliefs. Using data from nearly 11,500 adolescents ages 9-13, researchers tracked how expectations about the effects of alcohol, marijuana, and nicotine changed over time. The findings revealed that positive expectations about all three substances increased during early adolescence, while negative expectations showed different patterns: increasing for alcohol, decreasing for marijuana, and staying stable for nicotine. This suggests adolescents are developing increasingly optimistic views about marijuana's effects during these critical developmental years.

The study's most important finding relates to peer influence as a powerful driver of these changing beliefs. Adolescents with deviant peer affiliations (friends engaged in problem behaviors) showed steeper increases in positive substance use expectations across all substances. Conversely, adolescents whose peers expressed intolerance of substance use developed lower positive and higher negative expectations. This peer influence operated consistently across time, suggesting it's not a one-time effect but an ongoing dynamic process during early adolescence. These cognitive patterns—the beliefs and expectations teenagers hold—are critical precursors to actual substance use behavior.

The research has significant implications for prevention efforts. Rather than simply providing information about substance risks, interventions may need to address the social environments that shape adolescent beliefs. The finding that peer intolerance provides protective effects suggests that fostering peer norms against substance use, including marijuana, could help counter the developing positive expectations that increase vulnerability to future use. Understanding these developmental trajectories helps explain why peer influence is so powerful during adolescence and points to intervention targets that work with—rather than against—the natural social forces shaping teenage thinking.