Newly published results from a clinical trial testing the effects of cannabidiol (CBD) oil on symptoms of pain and distress in cancer patients suggest the popular product may be no more effective than a placebo. The findings add to an inconclusive body of research on the effects of medicinal cannabis for pain.
The new study is the first data to come from a series of three clinical trials studying the effects of medical cannabis on patients in palliative care with advanced cancer. Janet Hardy, from the Mater Research Institute and lead researcher on the project, said the work is trying to understand the optimal doses and uses for medical cannabis.
“The best way to describe the uptake of medicinal cannabis following its legalization was as a social phenomenon – everyone wanted it, but there was little evidence to guide its usage,” Hardy explained. “Usually, new products entering the market have gone through extensive pre-clinical studies regarding best dosage and usage, however, medicinal cannabis entered the market with very little guidance.”
This first trial focused on CBD oil, recruiting 144 patients in palliative care and randomly allocating them either a placebo or a self-titrated dose of CBD oil up to 600 mg per day. The primary metric used to measure the effects of the CBD was a total symptom distress score (TSDS) from a tool called the Edmonton Symptom Assessment Scale [ESAS]. This scale measures nine common symptoms in patients with advanced cancer and is frequently used in palliative care contexts.
After 14 days, the researchers saw no difference on TSDS measures between CBD and placebo groups. No difference was found on all other secondary measures up to 28 days, with around two-thirds of both placebo and CBD groups reporting “feeling better or much better” at the end of the study period.
“The trial found there was no detectable effect of CBD on change in physical or emotional functioning, overall quality of life, fatigue, nausea and vomiting, pain, dyspnoea or appetite loss,” Hardy noted. “There was no demonstration of an improvement in symptom control from CBD oil in patients with advanced cancer over that obtained from palliative care alone.”
The new findings come alongside another recently published study investigating the strength of the placebo effect in medical cannabis trials for pain. The research, led by a team from the Karolinska Institutet in Sweden, looked at 20 randomized controlled trials investigating cannabis for the treatment of pain.
That research found no significant difference on pain measures between cannabis and placebo. The study also accounted for trials where blinding was broken, meaning participants could tell when they were given cannabis or a placebo. The researchers suggest when participants cannot tell what they have been given they tend to rate the placebo as highly effective.
Interestingly, Hardy points out a strong placebo effect was detected in her team’s trial. And several participants in the placebo group even went on to buy CBD products after the trial had completed.
“Despite the lack of evidence of benefit, more than one third (36%) of participants in the first study elected to purchase a medicinal cannabis product after the trial, despite being unaware if they were taking the CBD or placebo,” Hardy said.
The remaining two clinical trials Hardy is working on are looking at similar measures of distress in palliative care patients, but using different combinations of CBD and the more psychoactive cannabinoid THC.
The new study was published in The Journal of Clinical Oncology.
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