The Cumulative Index to Nursing and Allied Health Literature draws information from more than 3000 journals.  To limit your CINAHL search to evidence-producing studies, there are numerous options.  Here are a couple of suggestions:

Suggestion 1:

1. Click on Advanced Search under the search box
2. Enter your search terms
3. Scroll to the bottom of the Advanced Search screen, and under Special Interest select Evidence-Based Practice

Suggestion 2:

1. Click on Advanced Search under the search box
2. Enter your search terms
3. Scroll down and check the box next to Research Article (research needs to be done in order for there to be evidence)