Cannabis Extracts Don’t Effectively Relieve Cancer Pain, Review Finds
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The validity of medicinal marijuana’s most celebrated benefit, pain reduction, has been called into question by a new review.
Published in the British Medical Journal today, the systematic review of six randomised controlled trials (RCTs) found that cannabinoids were no different to placebos when it came to changing patients’ average pain scores.
All trials assessed in the review examined the effects of cannabinoid extracts, such as Sativex, rather than flower-based medicinal cannabis, so its conclusions may not be entirely applicable to many patients’ products.
Cannabis and cancer
Chronic pain relief is one of the most oft-cited reasons patients seek out medical cannabis. And as up to 60 percent of anti-cancer therapy patients report related pain, the interest in cannabis-cancer pain treatment seems to be steadily growing alongside marijuana’s increasing acceptance.
In one anonymous survey conducted in a US state with legalized cannabis, 21 percent of adult cancer patients had used cannabis in the last month, most frequently for pain relief.
But, according to the new review, the science supporting these prescriptions is scarce.
“I think there is great interest in cannabinoid medicines from the general public at the moment,” Mike Bennett, a professor of palliative medicine at the University of Leeds and co-author of the review, told Analytical Cannabis. “But in cancer pain, using this particular product, we can't see a positive benefit.”
To reach their conclusions, Bennett and his colleagues re-assessed six RCTs in a systematic review and five studies in a meta-analysis.
Every trial was deemed to have a low risk of bias. All had tested the effects of pharmaceutical-grade cannabis, such as the THC:CBD mouth spray Sativex, rather than flower-based products. And in all trials, patients were also given opioids concurrently with their cannabis medications (or placebos).
“I think it probably reflects the reality that patients with persistent cancer pain are often on existing analgesia, particularly opioids,” Bennett clarified. “I think in practice we're most interested in seeing if cannabinoids add any extra value to opioids for pain management.”
But after their calculations were done, the authors found no difference between the cannabinoids and placebos with regards to changes in average pain scores.
“We use the common outcome measure for pain, which is a simple 0-10 rating scale,” Bennett explained. “So, patients were asked in the trials, what was your average pain over the previous 24 hours? It can be difficult to conceptualize an experience like pain into a simple number, but that's the industry standard in terms of trials of pain.”
“But as you can see, we found no overall differences in pain intensity between the trials in the meta analysis.”
Cannabis for pain
Many participants also experienced unpleasant side effects during the trials. In the worst cases, patients’ dizziness and fatigue caused them to dropout from the trials. Dropouts were less prevalent in the placebo groups, but the difference wasn’t deemed statistically significant.
“We found dizziness and sleepiness were the two key side effects that were more frequent for the cannabinoids,” Bennett told Analytical Cannabis. “And we don't know whether that's an effect purely of the cannabinoids, or whether there's some interaction between cannabinoids and opioids that produce that. I think the truth might be in the latter.”
Despite their results, the authors haven’t’ entirely ruled out cannabis’ potential as a pain-relieving medication. To make a decisive conclusion, more studies will be needed, especially those involving flower-based cannabis.
“In terms of the trial design, it may be that there are benefits but they’re not being picked up by the outcome we use, which is pain intensity,” Bennet said. “There may be small effects on pain, but we can’t detect those. And any effects come at the expense of more side effects.”
“So, I think for now, the evidence doesn't support these cannabinoid medicines for the management of cancer pain. But I can imagine that more research using different sorts of cannabinoid products and different outcome measures might need to be done to me more certain.”
Speaking to Analytical Cannabis in September last year, cannabis-cancer researcher Dr David Meiri also voiced his scepticism of marijuana’s pain-relieving properties, but espoused a more holistic approach to treatment.
“If you look in very specific and narrow window on pain, you would say it's not good,” he said. “If you look how I think you should look on cannabis policy – more holistic and doing other things that are related to pain and depression, sleep, anxiety – now you're treating all of them and the patient is much, much better. If you look just to measure a very, very narrow question, then you will fail.”