Randomized controlled trials (RCTs) are important for evaluating interventions, and qualitative research is increasingly recognized as being crucial to the success of this enterprise. We aimed to describe and demonstrate a temporal parallel purpose framework to help researchers understand how to make optimum use of qualitative research before, during and after RCTs. This framework sets out specific rationales for conducting qualitative research at each stage of a trial, where the rationales presented relate to both the intervention and evaluation methodology.

We conducted a scoping review of published qualitative studies undertaken alongside RCTs focusing on illicit drug use. We then used the temporal parallel purpose framework to present key findings to demonstrate how qualitative studies can add value to addiction RCTs by enhancing understanding of the intervention being trialled and/or the RCT itself. In so doing, we highlight the missed opportunities for addiction science when qualitative research is overlooked. We also explain why barriers to combining qualitative research and RCTs are neither inevitable nor insurmountable.

The temporal parallel purpose framework provides a tool for assessing when and why to combine qualitative research with addiction treatment and prevention RCTs. Our paper and framework can help researchers formulate key questions that qualitative research can address. This can potentially save resources by reducing the number of poorly designed interventions and trials and prevent morbidity, mortality, and other addiction-related harms by facilitating the identification and implementation of interventions that are most likely to be effective.