Often referred to as the "evidence pyramid," this graphic illustrates different types of research designs and the quantity of each study type in the body of published literature.
For Intervention Questions:
Randomized controlled trials (RCTs) are primary studies designed to test the effectiveness and efficacy of an intervention. These are considered the strongest study design for treatment/ intervention questions.
Meta-analyses and Systematic Reviews - are secondary studies of primary research. These "filtered sources" provide quick and concise evidence summaries on which to base intervention decisions.
Because RCTs are often not practical, or ethical, or even relevant to certain drug and alcohol related questions, you may need to rely on other study types (Quasi-experimental, Cohort, Case control, Case reports) to inform practice decisions.