Abstract
Participants in clinical trials of interventions for substance use frequently show substantial pre-treatment reductions in use. However, pre-treatment change has not been studied among pregnant women, a group with unique motivational characteristics. It is also not clear whether pre-treatment reduction in substance use can be clearly linked to research activities such as pre-treatment assessment, or if it is the result of more general factors such as the decision to seek treatment. Using an interrupted longitudinal design, we evaluated pre-treatment change among 148 pregnant women, all of whom had completed a clinical trial comparing motivational enhancement therapy to treatment as usual. When baseline period was compared to the period after randomization and before treatment, the change in substance use was substantial (dropping from an average of substance use on 30.5% of days during baseline to 16.7% of days during the pre-treatment phase; p<.001), and was greater in magnitude than change following initiation of study-related treatment. Further, this reduction was significant after controlling for a longitudinal time effect and did not apply to tobacco use. These findings suggest that change following pre-treatment research activities is independent of the decision to seek treatment and is present even among pregnant women, many of whom have already reduced their substance use. These findings also suggest the possible need for re-evaluation of the nature and causes of behavior change, as well as trial design, in clinical trials for substance abuse.