Canadian coverage

Hi, I'm new here and asking a lot of questions!

We live in Ontario, Canada, and my husband is not as yet formally diagnosed. In order to be diagnosed by a specialist, we need a referral from our GP. She is new to us, and doesn't know my husband well enough to go on anything but our word. Still I think we will be able to convince her about the need for an appointment.

Well in any case, I would like to know what is covered by OHIP in diagnosis, treatments and/or medication.

Anyone have any experience with this?