Predictive and discriminant validity of the Impaired Control Scale - Cannabis (ICS-C): an intensive longitudinal study of daily cannabis use outcomes.

Impaired control over substance use - difficulty adhering to limits on consumption - is a core feature of problematic use and addiction. Although extensively studied in alcohol research, impaired control over cannabis remains understudied. To advance research in this area, we evaluated the predictive and discriminant validity of the Impaired Control Scale-Cannabis (ICS-C) using an intensive longitudinal design. Young adults (N = 147; Mage = 22.07) who reported regular use of cannabis and alcohol completed three 21-day ecological momentary assessment (EMA) bursts spaced six months apart. The ICS-C was administered prior to each burst, followed by daily surveys assessing difficulty limiting use, substance consumption, and consequences. Three-level multilevel models examined whether ICS-C scores predicted cannabis outcomes observed on the daily surveys and whether daily reports of difficulty limiting cannabis use mediated these associations. The Perceived Impaired Control subscale demonstrated strong predictive validity: Within-person increases in perceived impaired control across bursts predicted greater difficulty limiting cannabis use in daily life, which in turn mediated associations with heavier cannabis consumption and use of multiple forms of cannabis. At the between-person level, the Attempted Control subscale predicted negative consequences through difficulty limiting cannabis use. The ICS-C also demonstrated discriminant validity, showing no significant associations with alcohol outcomes after controlling for cannabis use. The ICS-C, particularly the Perceived Impaired Control subscale, captures meaningful within-person fluctuations in self-regulatory capacity that predict real-world cannabis use patterns. Findings support the ICS-C as a valid tool for examining impaired control over cannabis across multiple temporal levels.