Interestingly enough, the way our receptors in our brain deal with cannabinoids is purely genetic. I have read studies where they have taken whole family groups with genetic conditions (such as asthma) and treated them with a variety of drugs, marijuana included, and found that certain families (even certain ethnicities) react to the cannabis the same way. For example, I remember reading about how they took four separate family groups (black, white, asian, and mexican) that all had arthritis, and gave them marijuana to see how well it treated their condition. Every one in the Asian, black and White families said it helped their pain and made it easier for them to use their hands/fingers, and other joints (even the ones that were against marijuana before the study, they didn't tell the families it was marijuana they were using, they told them what specific chemicals inside the cannabis they were using to treat them, and the administered it through carrot cakes believe it or not). Only one person in the Mexican family said it helped (and I honestly think its because she already smoked on a regular basis), every one else said that while some of the pain went away (but certainly not all), they still experienced difficulty in moving some of their joints. Further studies showed that when they gave the subjects MRI's and CAT scans, they could see the cannabis receptors reacting slightly different to the the CBD's/CBN's in each family group. According to the studies they did, different signals were sent through the spinal columns of the subjects, with different messages to the muscles and nerve endings, and for the mexican family most of the activity went strait to their muscles, while there nerves didn't get the affect as much. The repeated the tests like five times, and for different symptoms with many many more family groups, and concluded that the way a person processes the chemicals in cannabis is genetic, and that there are many promising treatment alternatives that can come out of furthering their studies (I think they put that last part in there to see if they could get more funding some how for more research). There are pain dulling chemicals in Cannabis, and enough cerebral activity comes out of using it, that it also distracts users from pain. The best way to use Cannabis for pain is to ingest Indica Dominant strains through food or eating it, while simultaneously smoking a Sativa dominant strain.
I read about the studies in a magazine a few months ago, I am going to try to see if I can find the articles online any where... hope this helped though...