Researchers reveal results of world's longest study into cannabis and opioids to treat pain

A large study on cannabis has uncovered some unexpected results. Photo / 123RF

It's safe to say most people think cannabis chills you out.

Now researchers have discovered that perception may be stronger than the drug itself.

In a large study of the effect cannabis has on pain in sufferers across Australia, the team from the National Drug and Alcohol Research Centre (NDARC) uncovered some unexpected results.

While they found most people "perceived it to help", in reality, it didn't really change their level of pain.

Researchers think this might be simply because medicinal cannabis can help people sleep so their pain is more tolerable the next day.

The University of New South Wales study followed 1500 people over four years to see how pain interfered with their everyday life and whether using medicinal cannabis would change their prescribed opioid use.

Worldwide interest in the area has been growing, particularly for chronic non-cancer pain.

There has also been increasing speculation that using cannabis for pain may allow people to reduce their prescribed opioid.

The results, published in Lancet Public Health on Tuesday, suggest that there is a need for caution given there were "no strong findings supporting a clear role for cannabis for these reasons".

Participants who were using cannabis had greater pain and anxiety, were not coping as well with their pain, and reported that pain was interfering more in their life.

They found there was no clear evidence that cannabis reduced pain severity or pain interference or led participants to reduce their opioid use or dose.

NDARC director Professor Michael Farrell said medicinal cannabis had been a very hard sell and people needed to approach it with caution.

"People who otherwise wouldn't have gone near cannabis have been experimenting with it," he said.

"One of the things we think happens when people report benefits is the sleep and sedation effects it has.

"Often when you get a good night's sleep your pain is a lot more tolerable."

In what was one of the world's longest in-depth community studies on pharmaceutical opioids and chronic non-cancer pain, participants were recruited through community pharmacies and completed comprehensive assessments of their pain, physical and mental health, medication and cannabis use annually.

They had been in pain for a median of 10 years and taken prescribed opioids for their pain for a median of four years, with "very high rates of physical and mental health problems".

Lead author Dr Gabrielle Campbell said chronic non-cancer pain was a complex problem.

"For most people, there is unlikely to be a single effective treatment," she said.

"In our study of people living with chronic non-cancer pain who were prescribed pharmaceutical opioids, despite reporting perceived benefits from cannabis use, we found no strong evidence that cannabis use reduced participants' pain or opioid use over time."