But British researchers say they have verified via MRI brain scans that the active ingredient in cannabis can ease pain.
That's proof positive, innit? Well, not just yet:
The researchers from Oxford University say the scans of 12 otherwise healthy men who suffered from pain show "reduced activity in key areas of the brain that substantiated the pain relief" and that pain was "more bearable" with a bag of weed, so to speak, according to a summary.
MRI scans matched the subjects' self-reporting that pot helped make the pain tolerable (though, researchers say, it didn't appear to reduce "intensity" of the actual pain):
The change in unpleasantness of pain was matched with a suppression of activity in the part of the brain called the anterior mid-cingulate cortex. This structure sits in a deep part of the brain and is involved in many functions, and has previously been implicated in the emotional aspects of pain.
There were also changes in activity of the right amygdala that correlated with the lessening in the unpleasantness of the pain with THC. It is already known that the right side of the amygdala can be 'primed' by pain.
The problem, according to the study, published in the journal Pain, is that cannabis affects the "emotional" response to pain and not the actual physicality of it. But, as many doctors and medical professionals have come to believe, that can be just as important.
Oxford's Michael Lee says more research is needed:
My view is the findings are of interest scientifically but it remains to see how they impact the debate about use of cannabis-based medicines. Understanding cannabis' effects on clinical outcomes, or the quality of life of those suffering chronic pain, would need research in patients over long time periods.