Cannabis makes pain more bearable instead of reducing it, say scientists
Patients took a combination of a placebo or a cannabis pill and had a normal cream or a painful chilli cream applied to the skin
They felt same intensity of pain from chilli cream when taking cannabis rather than placeboHowever, they did report that the pain bothered them less after taking the cannabis pill
Scans revealed cannabis reduced brain activity in areas linked to emotional reactions



14:22 GMT, 24 December 2012

Cannabis can make patients feel less bothered about pain, according to a study.

Researchers from the University of Oxford have found the psychoactive ingredient in cannabis doesn't reduce the intensity of pain, rather it makes it more bearable.

Brain scans revealed the ingredient known as THC, reduced activity in areas linked to the emotional aspects of suffering.

A man suffers from back ache

A man smokes a joint

While some patients have found cannabis to relieve chronic pain such as sciatica it has little effect on others, say scientists

While this had a strong relieving effect on some patients, it seemed to make little difference to the pain experienced by others.

Lead researcher Dr Michael Lee, said: 'Cannabis does not seem to act like a conventional pain medicine. Some people respond really well, others not at all, or even poorly.

'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 carried out this study to try and get at what is happening when someone experiences pain relief using cannabis,' says Dr Lee.

The researchers recruited 12 healthy men for the study. They were given either a 15mg tablet of THC or a placebo. They then had a cream rubbed into their skin to induce pain. Some were given a dummy cream while the rest receiving a chilli cream that caused a burning sensation.

The study was performed three more times, switching one aspect of the test for each volunteer. The patient also had four MRI tests to cover each combination.

'The participants were asked to report
the intensity and unpleasantness of the pain: how much it burned and how
much it bothered them,' says Dr Lee.

'We found that with THC, on
average people didn't report any change in the burn, but the pain
bothered them less.'

The cannabis plant: It is illegal to have, give away or sell the Class B drug. However, it is being used in medical trials

The cannabis plant: It is illegal to have, give away or sell the Class B drug. However, it is being used in a number of medical trials

Of most interest to the researchers was the strength of the connection in individuals between their right amydala and a part of the cortex called the primary sensorimotor area.

The strength of this connection in individual participants correlated well with THC's different effects on the pain that that volunteer experienced.

This suggests that there might be a way of predicting who would see benefits from taking cannabis for pain relief.

'We may in future be able to predict who will respond to cannabis, but we would need to do studies in patients with chronic pain over longer time periods,' says Dr Lee.

Cannabis is a Class B drug, which means it is illegal to have for yourself, give away or sell. While THC can make users feel relaxed it can also cause hallucinations and make people feel paranoid.

The latest study has been published in the journal Pain. It was funded by the UK Medical Research Council and the National Institute for Health Research (NIHR) Oxford Biomedical Research Centre.