I don't know about meds affecting the datscan. I phoned the helpline before mine because I had some questions I needed answering about it and they were very patient and helpful. So please don't be hesitant about phoning the helpline, they are very good.
My datscan seemed normal but the movementent disorder specialist hasn't given up on me, my symptoms have been steadily growing worse and there is something clearly wrong so they are going to admit me into hospital for a few days (at some time still to be determined) to see if they can work it out. So try not to panic about results, you won't be cast aside if they are not as expected.
If your meds are helping your symptoms, then the neurologist must be on the right track. You will find a lot of people will advise worry and stress will make symptoms worse, so try not to worry too much, easier said than done, I know.
All the best