The next step is to try out a few literature searches. These are also known as Scoping searches.
They are not comprehensive searches but you are looking to see if your topic area is reviewable.
For example, the scoping search results can quickly identify
Remember you need enough research to identify, critically appraise and synthesise information for your review. Can you widen the scope of your topic? Think about interventions, outcomes etc.
You can check other databases too:
See the Google Scholar section in Why do I Need the Library...why can't I just use Google? for more advice, pros and cons of using Google Scholar
Scopus can be a great database for mental health searches