In past three years I've had 5 MRIs. For the one on my shoulder, using contrast, I was prescribed a corticosteroid and took benadryl prior as I have a known allergy to some contrast media. No problems. I had two MRI of head. First one without contrast. Second one a few weeks later they did without contrast and, in same session, with contrast. I did not premedicate for that, and had no problems.
I would suggest talking with doctor and reporting any allergies you've had in the past to anything. That might give indication to doctor if you might have issues.
My father had pretty severe allergies to most contrast media. He had many, many, scans of different types, over the years, was premedicated, and had no issues.
Hope this helps. And yes the gas after digestive system scans is horrible. Don't laugh.... if you can get someone to help you get in a position where your lower body is up in the air, way above your head, you can possibly get rid of gas faster. I've done that twice with surgery that involved messing with my intestines. DH helped me "sort of" do a hand stand. Worked.
gg=alice