Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. Effective management of a patient's pain is a key part of cancer care and various medicines have been suggested to help with this. These include cannabis-based medicines and medical cannabis, and in June 2023, we published a new Cochrane review of their effects. Here's one of the authors, Andrew Moore, a retired scientist formerly at the University of Oxford speaking from the depths of Devon in the UK, to tell us about the review's findings.

Andrew: 30% to 50% of people with cancer experience moderate-to-severe pain, which can have a major negative impact on their quality of life. Morphine-like medications are commonly used to treat this pain, and are recommended in the World Health Organization pain treatment ladder. However, cancer pain is not sufficiently relieved by these opioid medications in 10% to 15% of people with cancer.
As alternatives, several products based on the cannabis plant have been suggested as treatments for cancer pain. These include inhaled or orally ingested herbal cannabis, so-called medical cannabis, and various oils, sprays or tablets containing the active cannabis ingredients, called cannabinoids, which are obtained from the plant, or made synthetically.  The most important of these are tetrahydrocannabinol, THC for short and cannabidiol, CBD.
Some people with cancer pain have reported that cannabis-based medicines do relieve their pain and the potential efficacy is often highlighted in the media. This makes it important to review the research evidence and, having done so for our Cochrane review, our assessment of studies of the benefits and harms of cannabis-based medicines, including medical cannabis, is that, on average, these medicines do not reduce pain in adults with cancer.
In total, we found 14 studies, for the review involving just over 1800 patients with cancer. The largest study included 399 people and the smallest study included 10. The studies were conducted in countries around the world with the largest group, six, based in North America.
Turning to the results, we found moderate-certainty evidence from five randomised trials involving 1539 participants that oromucosal nabiximols, that is THC and CBD in a nearly balanced ratio, or THC alone were ineffective in relieving moderate-to-severe cancer pain that had not responded to opioids. There was also low-certainty evidence from two randomised trials involving 89 participants that nabilone, a synthetic THC-analogue, was ineffective in reducing pain associated with (radio-) chemotherapy in people with head and neck cancer and non-small cell lung cancer. Two studies, with 66 people, that compared a single dose of synthetic THC analogues to a single low-dose morphine equivalent provided low-certainty evidence that the cannabis medication was not better for reducing moderate-to-severe cancer pain. Finally, we found low-certainty evidence in a single study with 144 participants that CBD did not add value to specialist palliative care alone in the reduction of pain in people with advanced cancer.
In summary, therefore, our review has shown that cannabis-based medicines were not effective in reducing cancer pain in the studies done to date.

Mike: If you'd like to read more about these studies and the conclusions of the review, it's available online at Cochrane Library dot com with a simple search for 'cannabis and cancer'.