In the UK, the standing of cannabis as a member of the analgesic pharmacopoeia is somewhat nebulous, and there are strong opinions on both sides about whether there is enough evidence for its effectiveness.
For many experts, it was a victory for evidence-based medicine when the 2019 National Institute for Health and Care Excellence (NICE) guidelines failed to recommend cannabis for treating pain. But, for cannabis advocates, it robbed hundreds of thousands of people of potentially life-changing therapy.
This stand-off continues today and at its core lies the question of what type of evidence counts when it comes to making clinical decisions.
Advocates say that evidence of humans consuming cannabis for therapeutic purposes for millennia and the millions of people currently taking it for pain relief — both legally and illegally — is a testament to its value.
Cannabis isn’t a wonder drug; there are people on the internet that say it cures everything known to man — of course it doesn’t, Mike Barnes, a former neurologist and founder of the Medical Cannabis Clinicians Society and Cannabis Industry Council
“Cannabis isn’t a wonder drug. There are people on the internet that say it cures everything known to man — of course it doesn’t,” says Mike Barnes, a former neurologist who founded and is now president of the UK’s Medical Cannabis Clinicians Society.
“It’s just another medicine. It’s not suitable for everybody. It doesn’t help everybody. But it is very, very useful.”
Barnes, who also founded and now chairs the Cannabis Industry Council, believes that when NICE and other major medical societies advised against using cannabis as an analgesic, they “ignored the real-world evidence — of which there is a great deal — that demonstrates that cannabis is very useful for pain”.
However, many dedicated pain researchers have a different view. They do not dismiss cannabis entirely, but what troubles them is that, when it comes to using it for pain relief, there is simply no evidence of the type that modern medicine routinely requires to approve a treatment.
Such data come predominantly from well-conducted randomised controlled trials (RCTs) — evidence-based medicine’s gold standard. But in the case of cannabis, Andrew Rice, president-elect of the International Association for the Study of Pain (IASP) and a pain clinician and researcher at Imperial College London, says: “The trials that have been done don’t show an analgesic effect for pain.”
The few that have are of too low a quality to take seriously, Rice says, which points to a wider problem: good quality trials — RCTs especially — are few and far between.
In 2018, the IASP — concerned with snowballing medical cannabis use across the world — commissioned a major review of the literature, examining RCTs, systematic reviews, preclinical science and safety.
One caveat that emerged was the massive variety of cannabis-related products tested as putative analgesics. ‘Cannabis-based medicine’ (CBM) is an umbrella term covering everything from unprocessed plant material, resins and oils — all containing vast mixtures of bioactive compounds, which vary from strain to strain — through to preparations of single cannabinoids (mainly THC and CBD), onto more tightly controlled pharmaceutical products containing different but known quantities of cannabinoids. Consequently, few studies looked at exactly the same intervention.
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