Severe pain from Arthritis is a Health Canada accepted Category 1 condition
Medical marijuana is NOT for everyone. Strong anecdotal evidence exists for the support of medical marijuana in treating pain and inflammation associated with arthritis. We strongly suggest you discuss the potential benefit of medical marijuana with your doctor or specialist
Arthritis literally means "joint inflammation". It consists of more than 100 different conditions. The common symptoms for all these conditions are joint and musculoskeletal pain, which is why they are all considered to be forms of “arthritis'. Often the pain associated with arthritis is a result of inflammation of the joint lining. Inflammation is the body's natural response to injury. The warning signs that inflammation presents are redness, swelling, heat and pain. When a joint becomes inflamed it can prevent the normal use of the joint and therefore it can cause the loss of function of that joint. 
Severe Forms of Arthritis 
Osteoarthritis (OA) is the most common type of arthritis. OA is characterized by worn cartilage or tissue that pads the bones in a joint.
Rheumatoid Arthritis is an autoimmune disease and is the second most common form of arthritis. With Rheumotoid Arthritis the body attacks the lining of a joint which leads to inflammation.
Gout is one of the most painful forms of arthritis. Gout is caused when crystals of uric acid form in the connective tissue and/or joint spaces.
Ankylosing spondylitis(AS) is a chronic, progressive, painful inflammatory rheumatic disease, which affects the spinal joints, in particular those at the base of the spine (the sacroiliac joints and the lumbar spine) 
Early diagnosis and appropriate management of arthritis, including self-management activities, can help people diagnosed with arthritis decrease pain, improve function and stay productive.
Take a look at the following websites for further information on self management of Arthritis:
Benefits of Marijuana
One of marijuana’s oldest recorded uses is relieving swelling and inflammation. Currently, modern scientist are exploring a network of cannabinoid receptor sites located throughout the body. This new understandings of cannabinoid research clearly supports the historical references on treating inflammation with marijuana. Different cannabinoids founds naturally in marijuana have different benefits for arthritis sufferers. Tetrahydroconnabinol (THC) is beneficial as a pain reliever. Cannabichromene (CBC) and cannabidiol (CBD) have been shown in clinical studies to have valuable anti-inflammatory properties.
Sativex(CBM)is a marijuana-based drug that was developed by GW Pharmaceuticals in 2005 as a treatment for Multiple Sclerosis. Sativex has however been shown to have beneficial effects in rheumatoid arthritis. Tests of Sativex on arthritis patients showed it helped reduce pain, and improve quality of sleep. Sativex is not psychoactive and comes in the form of a mouth spray composed mainly of two cannabinoids found naturally in marijuana, Tetrahydroconnabinol(THC) and cannabidiol(CBD).