Cannabis "not an effective pain reliever"

Liz Filmer
23 Jun 2022

A US Government-backed study of 25 trials has found very little scientifically valid evidence that it is an effective pain killer.

One of the researchers said: "In general, the limited amount of evidence surprised all of us. With so much buzz around cannabis-related products, and the easy availability of recreational and medical marijuana in many states, consumers and patients might assume there would be more evidence about the benefits and side effects. Unfortunately, there is very little scientifically valid research into most of these products". 

This latest review, by experts from Oregon Health and Science University and published in Annals of Internal Medicine, looked at the evidence from 18 placebo-controlled studies and seven long-term papers. A total of 14,835 people participated in the trials and took cannabis in differing forms for as long as 12 months.

Almost 15,000 people consumed a wide range of cannabis products, including plant material, edibles, CDB oils and synthetic cannabis tablets. No noticeable long-term pain relief was found in those who smoked or ingested cannabis products. The only product that showed a statistical benefit for pain was a synthetic cannabinol tablet that mimics the effects of THC. 

Patients were required to assess their pain levels before, during and several weeks after taking cannabis. The results showed that the synthetic product containing high levels of THC had a 'moderate effect' on pain reduction. In terms of side effects, however, it had a 'large effect' resulting in dizziness, nausea and tiredness.

Using cannabis flower failed to show any significant benefit. The results may have been tainted by methodological issues, including failing to record dose levels or side effects. However, all is not lost, and many are questioning whether the findings of this study are down to its execution rather than the fact that cannabis has no pain-relieving qualities. 

The review's authors stated: "Evidence for whole-plant products, CBD, and other cannabinoids was limited by severe imprecision and lack of ability to assess consistency and study methodological limitations". 

The link between psychosis and cannabis addiction was also not considered by the 'whole plant' studies, which is currently a significant concern about how cannabis may impact mental health.

In a commentary in the same journal, Other experts commented that the study may not have been able to prove the benefits of cannabis due to the limitations of the study rather than the fact that cannabis does not work in relieving pain.

"These limitations are well documented in the cannabinoid and chronic pain literature and are due partly to "War on Drugs" policies that have overwhelmingly favoured studying cannabis-related harms over cannabis-related benefits. Unfortunately, this review found limited evidence that could be used to inform long-term use of available cannabis products for chronic pain."

Researchers called on doctors not to be dismissive of using cannabis for chronic pain relief. They said instead that they should be pragmatic when dealing with patients who wish to try using cannabis for pain relief. 

'Conventional painkillers are effective only in a percentage of people, so it is no wonder many patients are drawn to widely available cannabis products. Clinicians can compassionately witness, record, and offer guidance to help patients with chronic pain use cannabis wisely.'

Cannabis is currently legal in 19 US states for recreational purposes and 38 states for medicinal use. Britain has few chronic pain treatment options, with NHS patients often prescribed powerful, addictive painkillers.

Around 15.5million people in England live with chronic pain conditions, whilst the number is nearer to 100million in the US. The NHS is set to try cannabis as a chronic pain treatment over the next three years, with the option of offering 'whole plant' medications.

Liz Filmer