Brain imaging insight into cannabis as a pain killer
The pain relief offered by cannabis varies greatly between individuals, a brain imaging study carried out at the University of Oxford suggests.
The researchers found that an oral tablet of THC, the psychoactive ingredient in cannabis, tended to make the experience of pain more bearable, rather than actually reduce the intensity of the pain.
MRI brain imaging showed reduced activity in key areas of the brain that substantiated the pain relief the study participants experienced.
'We have revealed new information about the neural basis of cannabis-induced pain relief,' says lead researcher Dr Michael Lee of Oxford University's Centre for Functional Magnetic Resonance Imaging of the Brain (FMRIB).
'Cannabis does not seem to act like a conventional pain medicine. Some people respond really well, others not at all, or even poorly,' he says. 'Brain imaging shows little reduction in the brain regions that code for the sensation of pain, which is what we tend to see with drugs like opiates. Instead cannabis appears to mainly affect the emotional reaction to pain in a highly variable way.'
Long-term pain, often without clear cause, is a complex healthcare problem. Different approaches are often needed to help patient manage pain, and can include medications, physiotherapy and other forms of physical therapy, and psychological support.
For a few patients, cannabis or cannabis-based medications remain effective when other drugs have failed to control pain, while others report very little effect of the drug on their pain but experience side-effects.
'We know little about cannabis and what aspects of pain it affects, or which people might see benefits over the side-effects or potential harms in the long term. We carried out this study to try and get at what is happening when someone experiences pain relief using cannabis,' says Dr Lee.
He adds: ‘Our small-scale study, in a controlled setting, involved 12 healthy men and only one of many compounds that can be derived from cannabis. That’s quite different from doing a study with patients.
'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.'
(The paper ‘Amygdala activity contributes to the dissociative effect of cannabis on pain perception' by Michael C. Lee, Markus Ploner, Katja Wiech, Ulrike Bingel, Vishvarani Wanigasekera, Jonathan Brooks, David K. Menon, Irene Tracey (DOI: 10.1016/j.pain.2012.09.017) will appear in PAIN®, Volume 154, Issue 1 (January 2013) published by Elsevier)
