Good news for pot smokers: Researchers at the University of Oxford have uncovered evidence that cannabis may make enduring pain more bearable. However, researchers caution that the pain relief offered by marijuana differs greatly between individuals.

Researchers discovered that an oral tablet of THC, the psychoactive ingredient in cannabis, seems to make pain more bearable, as opposed to actually reducing the intensity of the pain. A brain imaging study found reduced activity in key areas of the brain that provided proof of the pain relief that the study participants felt.

“We have revealed new information about the neural basis of cannabis-induced pain relief,” says Michael Lee of Oxford University’s Centre for Functional Magnetic Resonance Imaging of the Brain. “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.”

For some patients, who suffer from long-term pain, cannabis or cannabis-based medications are suitable for controlling pain. Other patients, however, report that cannabis has very little effect on their pain.

“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 Mr. Lee.

Oxford researchers conducted several MRI scans with 12 participants at the FMRIB center in Oxford.

Prior to an MRI scan, participants were given either a 15mg tablet of THC or a placebo tablet.

To cause a certain level of pain, the participants had a cream rubbed into the skin of one leg. The cream was either a dummy cream or a cream that contained 1 percent capsaicin, the ingredient of chillis that leads to a burning and painful sensation.

“The participants were asked to report the intensity and unpleasantness of the pain: how much it burned and how much it bothered them,” says Mr. Lee. “We found that with THC, on average people didn’t report any change in the burn, but the pain bothered them less.”

Researchers found great variability among the participants in THC’s effect on the pain they felt. Only six out of the 12 reported a clear change in how much the pain bothered them, for example.

The brain imaging scans were able to verify the reports of the participants, leading researchers to believe that they may one day be able to predict whether cannabis would help a patient before prescribing it to him or her.

“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 Mr. Lee. “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.”

This study is making headlines as Colorado and Washington State pot smokers enjoy their cannabis without the fear of being arrested or cited for smoking weed. These states legalized the recreational use of marijuana in November.

“The significance of these events cannot be overstated,” said NORML, a pro-legalization organization, in a statement at the time. “Tonight, for the first time in history, two states have legalized and regulated the adult use and sale of cannabis.”

Although recreational marijuana use is now legal in Colorado and Washington State, there are some concerns that the federal government will eventually try to fight back against the recently-passed laws, as recreational marijuana use is still illegal under federal law.

The study’s findings were recently described in detail in the journal Pain.

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National Monitor