MySQL join same table on two fields

I have a table with two user id fields
I need to get the username in one query for each of the two ID's

When just grabbing one username the query is fine, trying to add the second username then I get timeouts

Here's a start of the query

SELECT * from threads left join users on users.id=thread_user 
left join users as user_last on users.id=thread_user_last 
where ref_id=26 order by thread_datetime desc limit 25

The query is limited to 25 rows, I can't see what is slowing it down