Full text search optimization

I have around 200 million sentences in my database and want to use the FTS to search through indexes.
My problem is that the full text search is not the fastest.

What are some suggestions I could try to optimize the search. The only thing I can think of is trying to use an analyzer that uses more stop words. Are there any other suggestions I might try. The sentences contain medical articles if that helps, so the queries will mostly be medical terms like sclerosis, etc...