Download the Arthritis PDF I attached that's from Americans for Safe Access. It has good medical info about cannabis and Arthritis.
My personal experience having RA and using cannabis:
I am in my early 30's and have RA and use cannabis to help with pain. I found that some cannabis works well for pain and others do very little or even make it worse. Like SeaMaiden said eating it is the best way to take it in my opinion. When eaten it takes about an hr to become active and lasts usually 3-5hrs. Eating cannabis helps relax the muscles, helps you sleep at night, helps distract from the pain, and lessens pain.
The second best way to take it is in a vaporizer. People with RA have weakened immune systems and smoking is more detrimental for us and takes us longer to heal from the damage cause by inhaling smoke.
Another product that helps me is
Dr. Greens cannabis lotion. It's made from shea butter and infused with cannabis and essential oils (i like lavender for relaxation).
CBD strains work best for pain and RA, Harlequin is the best I have found so far. If you don't have access to tested cannabis, 100 %Indica strains are the next best choice. They relax the body and help with muscle pain and joint pain and tension.