STUNNING HORSE! :)

I have never read or heard of any of this stuff interfering with B C, wise for you to ask. I really do not know about other medicines, but I never had a doctor tell me to stop taking the GLA oils.
My uneducated recommendation is to start small and build up. The pills for hemp oil tend to be 1 gram, the other oils may come in smaller amounts per pill. Hemp oil also comes straight (no pill), not exactly the most delightful thing in the world to take by mouth, but it has a sort of nutty flavor. The hemp powder I just mix with hot cereal when I take it (one scoop, but of course you can start with less.)
Of course if you are worried, ask your doctor. Just hope your doctor has some training in alternative therapies (though most of them don't know much about hemp powder and the efficacy of GLA for inflammations.) I did notice that MSM seemed to block the effect of the hemp powder for around three weeks (with the horse), then it seemed to kick in again.
The hemp seed powder is also a protein supplement, with many, many amino acids including all the essential ones our bodies can't make by themselves. Mia's hooves have gotten stronger and have grown faster since I started giving it to her, and her coat is nice and shiny.
Hope this helps!

Oh, I hit a key wrong. You can get all these oils and hemp powder in the natural food stores. Hemp powder is legal (no mental effects) in the USA and Canada for sure. I really hope this helps you, I've seen amazing improvement in the mare I ride.

Tiffany, I read your comment on the fitness challenge thread. I made a group for handicapped and disabled riders, I hope it is still there, get on it and you may find that there are people like you.
I have MS, and I am 59. Yes, I have problems, but woman, I do not have as many problems as you do. About your stiffness, I have had GREAT success with hemp powder with an arthritic Arabian mare. When she is off it she moves like she has sand in her joints, with it her movement is MUCH smoother. I use hemp oil when my joints act up. The Gamma-linolenic acid (GLA)in the powder or oil acts as an anti-inflammatory all over. Other sources for GLA are Evening Primrose oil, Borage seed oil, and Black Current seed oil. These are more expensive, but if you have to do drug testing the hemp seed oil/powder can trigger a false positive. The other oils with GLA do not have this problem.