Using Ecological Momentary Assessment to Identify Mechanisms of Change: An Application From a Pharmacotherapy Trial With Adolescent Cannabis Users

Abstract

Objective: The present study used youth's in vivo reports of subjective responses to cannabis while smoking in their natural environments to identify real-world mechanisms of topiramate treatment for cannabis misuse.

Method: Participants were 40 cannabis users (≥ twice weekly in past 30 days), ages 15-24 years (47.5% female), with at least one cannabis use episode during the final 3 weeks of a 6-week, randomized clinical trial. Youth reported subjective "high" while smoking, stimulation, sedation, stress, craving, and grams of marijuana used in the natural environment via wireless electronic devices. Bayesian multilevel structural equation modeling (MSEM) evaluated mediation via indirect effect tests.

Results: Significant within (daily) and between (person) variability and distinctive within and between effects supported the MSEM approach. Subjective high while smoking was significantly reduced for youth in the topiramate condition, relative to placebo, and the indirect effect of reduced subjective high on total grams of cannabis smoked that day was significant. Indirect effects through other subjective responses were not significant.

Conclusions: The results of this initial study suggest that altering subjective responses to smoking, specifically subjective high, may be a key target for developing adjunctive pharmacotherapies for cannabis misuse. More generally, this work provides an example for applying ecological momentary assessment and analytic techniques to evaluate mechanisms of behavior change in longitudinal data.

Figure 1.

Conceptual illustration of multilevel structural equation model showing disaggregation of within (daily) and between (person) effects. The medication condition variable had only between-group variance (i.e., participants were randomly assigned either active medication or placebo), and thus associations of medication condition and subjective-response mediators are specified only at the between level. The mediating variables and outcome were repeated measures with both within- and between-group variance. Subjective responses of “high,” craving, stimulation, sedation, and stress were assessed just after smoking, and total grams today was culled from morning reports of total grams of cannabis smoked the previous day. Within-level estimates of subjective responses and total grams today accounted for grams smoked at that smoking event to establish temporal precedence for initial subjective cannabis responses predicting subsequent smoking.