Tell me why: An ecological momentary assessment study of "unknown" substance use motive endorsement and the...

Theoretical models of substance use motives emphasize the role of affect when making decisions about use and propose that there are moments during which decisions about use are made outside of conscious awareness or without clarity about why. However, to our knowledge, no previous research has examined the frequency and phenomenology of this motivational state. This study sought to fill this gap by introducing an "I don't know" option to a substance use motive questionnaire ("unknown" motive).

Fifty young adults (age=18-24) with substance use disorder (32 % alcohol use disorder, 34 % cannabis use disorder, 34 % both) completed 14 days of EMA consisting of five random momentary assessments which inquired about affect and substance use in the past 30min. If participants reported use, motives for that use episode were assessed with a checklist (observations=293).

"Unknown" motive endorsement occurred in ~40 % of use moments. Negative affect displayed a positive quadratic relationship, such that lower- and higher-than-average negative affect were associated with a greater probability of endorsement compared to mean (ps ≤ .002). Positive affect displayed a negative quadratic relationship, such that person-mean positive affect was associated with a greater probability of endorsement (ps ≤ .001).

This was the first study to investigate the occurrence of "unknown" motive endorsement and its predictors. This endorsement appears to be common and may have non-linear associations in opposite directions with positive and negative affect, highlighting the unique role of affect in substance use.