Depending on who you listen to, medical cannabis is either a rising star in the world of therapeutics or an over-vaunted pariah that should never have exited the grubby world of the illicit street corner deal.
In October 2016, the Australian federal government legalised medicinal cannabis, paving the way for individual states to legislate its use for a range of conditions including intractable epilepsy, pain and nausea in cancer, and limb spasticity in multiple sclerosis.
Sensing opportunity, a number of companies are jostling for early position in what is estimated to be a 100 million dollar a year medical cannabis market. A recent exposé by current affairs programme Four Corners called it a “green rush”, replete with “marijuana moguls”.
The science, however, is decidedly patchy, plagued by poor quality studies and the challenge of giving standard doses of a drug with over 400 chemical ingredients – 60 of which are the cannabinoids implicated in pain relief, and others having opposing effects.
One recent review found “reasonable evidence” of benefit for nausea in chemotherapy. Another in children and adolescents found “increasing evidence of benefit for epilepsy”, but insufficient evidence to support use for spasticity and neuropathic pain, a burning sensation caused by oversensitive nerves.
A new study, led by Gabrielle Campbell from the Australia’s National Drug and Alcohol Research Centre (NDARC) at the University of New South Wales in Sydney is unlikely to induce cheer in either stockholders of medical cannabis companies, or patients desperate for relief.
Published in the journal Lancet Public Health, the research examined cannabis use over four years in a nationwide cohort of 1514 Australian adults with chronic non-cancer pain. Most had back or neck pain, neuropathic pain, or arthritis, and the median duration was 10 years. All were using some form of opioid drug, such as oxycodone or morphine, to control symptoms.
The researchers tracked cannabis use with interviews and self-report questionnaires, categorising participants as non-users, infrequent users, or daily/near-daily users.
The results were underwhelming.
At the four year mark, just under a quarter had used cannabis as a painkiller. Those who did, however, reported more severe pain and greater disruption to their daily lives. Users also clocked higher anxiety and were less likely to think they could carry on in spite of pain.
Further, the researchers found cannabis use bore no relation in time with changes in pain scores or level of functioning. Nor did cannabis lead to reduced dosage or discontinuation of opioid drugs.
“Cannabis use was common in people with chronic non-cancer pain who had been prescribed opioids, but we found no evidence that cannabis use improved patient outcomes,” the authors concluded.
The researchers did, however, find something perplexing. Cannabis users often felt better, and on average rated the drug seven out of 10 effective, despite a lack of objective improvement in their reported pain scores.
“It is really difficult to disentangle the reasons for this,” says Campbell. “One hypothesis is that it may improve sleep and subjective wellbeing.”
It’s worth noting the study took place mostly before medical cannabis was legalised, so the drug was often obtained illicitly and smoked. This potentially limits the relevance of findings for medical cannabis.
“Some of the medicinal formulations have higher concentrations of CBD [cannabidiol] … and also they may have higher doses or higher quality,” says Michael Farrell, director of NDARC and a co-investigator on the study.
Nonetheless, the negative findings raise questions about the pace of legislation to increase access to medical cannabis.
“We think that the Therapeutic Goods Administration has taken a balanced approach and it is important to try and promote access for those who feel it is important for them, but to continue to keep a careful eye on it and look at the evidence,” says Farrell.
“What is important here is that we try to moderate expectations people have around handling pain.”
Paul Biegler is a philosopher, physician and Adjunct Research Fellow in Bioethics at Monash University. He received the 2012 Australasian Association of Philosophy Media Prize and his book The Ethical Treatment of Depression (MIT Press 2011) won the Australian Museum Eureka Prize for Research in Ethics.
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