How much CBD oil (MG wise) to take for arthritis?

Hello everyone! I am going to be buying some CBD oil from a dispensary for my mother. She has really bad arthritis in her shoulder and the pain is becoming too much for her. She weighs about 120 pounds and has no history of marijuana usage...so her tolerance will be low. How much do you think would be a good starting dose (mg wise)?

I want to get her something "nonpsychoactive" so she doesn't get high on her first try.

I'll be getting something from an actual marijuana dispensary and not some gas station type CBD lol


Thank you!

I'm sure the staff at the dispensary will be better able to answer that question.