If you have already searched Ovid Medline:
Don't 'limit to humans'
If you select 'limit to humans' you risk losing all non-indexed and pre-print publications in a database which have not been indexed as 'human'. This could be thousands of records.
Instead, remove the animal studies
A safer alternative is to search for the things we don't want (in this case animal studies) and remove them from the results. Adjust the line numbers below as appropriate.
CINAHL example
S6. [last line of search - your line number will be different]
S7. (MH "Animals+") NOT (MH "Human")
S8. S6 not S7