JPBS

Background: Early substance use during adolescence increases the risk for later substance use disorders and mental health problems, yet the real-time emotional and contextual factors underlying these behaviors remain poorly understood. Methods: We analyzed approximately 23,000 substance use–related posts and an equal number of non–substance use posts from Reddit’s r/teenagers subreddit (2018–2022). Posts were annotated for discrete emotions (sadness, anger, joy, guilt, fear, shame, and disgust) and contextual influences (family, peers, and school) using large language models (LLMs). Group differences were assessed statistically, emotion–context associations were visualized using heatmaps, and an interpretable XGBoost model identified key predictors of substance-use discussions. In addition, LLM-based thematic analysis extracted latent psychosocial themes linking emotions with contexts, providing qualitative insight into adolescents’ lived experiences. Results: Negative emotions, particularly sadness, guilt, fear, and disgust, were more prevalent in substance use posts, while joy predominated in non-substance use discussions. Guilt and shame showed distinct patterns: guilt often signaled regret and reparative intent, whereas shame reinforced risky dynamics through peer identity performance. Peer influence emerged as the strongest contextual driver, closely associated with sadness, fear, and guilt. In contrast, family and school environments displayed dual roles, acting as both risk and protective contexts depending on relational quality and stressors. Conclusions: Adolescent substance use reflects the interplay of sadness, guilt, and peer influence as central risk factors, with family and school contexts can operate as sources of both risk and protection.

adolescent; large language models; reddit; substance use