["Journal of Research on Adolescence, Volume 36, Issue 2, June 2026. ", "\nAbstract\nDaily mood reactivity, or the extent to which positive and negative moods change in response to experiences, is both a marker of overall psychological health and a predictor of future health and well‐being. A preponderance of studies has focused on negative mood reactivity to stressful events, leaving gaps in knowledge about positive mood reactivity and the impact of positive daily experiences. We aimed to identify within‐person patterns of adolescent positive and negative mood reactivity to daily interpersonal interactions, test correlates of mood reactivity patterns, and determine whether adolescent reactivity patterns precipitated mental and behavioral health outcomes in young adulthood. We used latent profile analysis to identify the patterns of positive and negative mood reactivity among 316 racially diverse adolescents (Mage = 16.4 at Time 1) in the United States. Most adolescents were characterized by typical reactivity (86%), showing mood responses in expected directions and average in magnitude. Some adolescents were characterized by heightened reactivity across most daily interactions (generalized heightened reactivity, 7%) or heightened reactivity to certain types of daily interactions (selective heightened reactivity, 7%). Adolescents in the latter two profiles were characterized by greater life stress. Adolescent profile membership was associated with differential cigarette and marijuana use at age 20, with most results indicating higher risk among those with heightened daily mood reactivity. Findings can be used to inform personalized prevention efforts, especially for adolescents with high life stress who may be more likely to exhibit heightened daily mood reactivity and eventually elevated substance use.\n"]