To make sure you haven't missed any clinical trials in your database searching, you can also "Hand Search" or browse the Tables of Contents of a journal or conference proceeding over a certain number of years.

Dickersin, Scherer, & Lefebvre (1994) explain that this can be a useful addition to your database searching, to allow you to identify trials that have not been included indexed by databases. Even when clinical trials are included in the databases, they may not include relevant search terms in the abstract, title and keywords that allow them to be identified easily as trials.

Further Reading

Dickersin, K., Scherer, R., & Lefebvre, C. (1994). Identifying relevant studies for systematic reviews. BMJ, 309(6964), 1286-1291. doi: https://doi.org/10.1136/bmj.309.6964.1286

Identifying the most relevant journals to hand search is an important part of the approach. Both Scopus and Web of Science allow you to perform a search and then identify the journals that hold the most number of results.

Scopus

Run your search in Scopus

Select Analyze Search results at the top of the Results list

Scroll down and select the box that is displaying "Documents per year per source"

This will display the list of sources by number of results - this will identify the Journals you should be browsing

Web of Science

Run your search in Web of Science

Select Analyze Results at the top right of the results list

On the left menu, select Sources

The top level sources in the results will be displayed visually at the top of the page, scroll down to see a list.