Medical cannabis is a contentious subject. Advocates claim it has a wide range of potential benefits, and may be used to treat everything from chronic pain to nausea. Some users go further, saying it's the only thing that alleviates their symptoms. But what does the evidence suggest?
In 2016, an independent review on the subject concurred that the drug had legitimate medical uses. Recommending that the government 'moves to introduce a system that allows lawful access to medicinal cannabis', the authors, from the All Party Parliamentary Group (APPG) for Drug Policy Reform, concluded that the status quo is out of step with the evidence.
"We came to the overall conclusions that the risks were minimal, the benefits were potentially great and there's no doubt that the government should legalise medical cannabis," says Professor Mike Barnes, a neurologist and rehabilitation physician who compiled evidence for the report.
Cannabis and the law
If this does occur, it will spell a significant change to existing drug laws. Currently, cannabis is controlled as a class B drug, punishable with up to five years in prison for possession. Medically speaking it is Schedule 1, a category for drugs with 'no therapeutic value'.
This hardline stance leaves many people unable to access a substance they regard as a medicine. (For obvious reasons, it's difficult to estimate how many people in the UK are self-medicating with herbal cannabis, but the report places the figure somewhere in between 30,000 and 1 million) It also creates obstacles for researchers who want to conduct clinical trials into the drug's medicinal uses.
Frank Warburton, a consultant and research officer who contributed heavily to the report, has strong words to say on the subject.
"The law on medicinal cannabis in the UK is complicated, illogical and nonsensical," he says. "You've got a situation where the two main constituents of the plant taken separately are considered to have medicinal value, but cannabis as a whole doesn't have medicinal value, even though there's no explanation as to how."
He is referring to tetrahydrocannabinol (THC) and cannabidiol (CBD), two compounds that are present in the cannabis plant in varying quantities. In the UK, doctors are allowed to prescribe nabilone (a synthetic analogue of THC) off licence for pain management. Meanwhile, CBD is easily accessible for UK consumers, and is even sold at Holland & Barrett.
A derivative of herbal cannabis, Sativex®, has also been approved to treat neuropathic pain and spasticity.
"Sativex® doesn't have a NICE recommendation and it's not available on prescription in England, but it is available in Wales," says Warburton. "So there's not only a basic contradiction between the laws surrounding herbal cannabis and Sativex®, but there's a patchwork of different policies across the country as well."
The Alfie Dingley case
It's a confusing situation, and one that has made national news with the recent Alfie Dingley case. A 6-year-old boy with a rare genetic form of epilepsy, Alfie can suffer up to 30 violent seizures a day. While his condition can be managed with steroids, these drugs are toxic to the body and will likely cause organ failure or psychosis over time.
Last year, Alfie and his family travelled to the Netherlands, where he was treated with cannabis oil. His seizures all but vanished. However, since returning to the UK, he has been forced to return to his regime of intravenous steroids. His mother is currently pleading with the UK government to 'make an exception for Alfie and grant his doctor licence to prescribe medical cannabis'.
At the time of writing, an online petition has amassed nearly 400,000 signatures and the Home Office says it is 'exploring every option'. It may be that his doctor is granted a licence on compassionate grounds.
The evidence base
So aside from exceptional cases of this kind, what does the evidence actually say about the benefits of medical cannabis? And conversely, what do we know about the risks?
Barnes, who sifted through around 20,000 studies for the report, says the evidence for some indications is more clear-cut than for others.
"We were asked to review the literature for the efficacy of cannabis and the associated side effects, and I was quite surprised at the depth of evidence, given that it's illegal and difficult to do drug trials on it," he says. "There was good evidence that cannabis helps muscle spasticity, chronic pain, nausea and vomiting in chemotherapy, and anxiety. There was slightly less, but nevertheless reasonable, evidence that it helps fibromyalgia, PTSD and epilepsy. If we'd written the report now we'd have put epilepsy in the good evidence category."
He says that CBD, the cannabis-derived compound you can buy in shops, appears to have some of the same benefits.
"CBD does a few things in its own right - it treats anxiety, has an analgesic (painkilling) effect and has a very positive effect on epilepsy," he says. "However, the evidence is that the cannabis plant in total is much better than CBD for indications like pain, because all the different chemicals in the plant act in synergy. Some of the children we're hearing about with epilepsy do improve on CBD, but they improve more on cannabis extract."
Side effects and risks
In terms of the harms, the report found that the short-term side effects of cannabis were generally mild and well tolerated - they included drowsiness, a dry mouth and some dizziness. However, around 8.5% of medicinal users reported significant side effects, and 9% of users developed a dependency.
Regarding the much-discussed connection between cannabis use and schizophrenia, Barnes says there is probably a small link, at least among those who start using cannabis young and have a genetic predisposition. Since teenagers' brains are still maturing, it is thought that cannabis use could disrupt that development.
There is currently a large-scale study underway in the USA, tracing how different substances and lifestyle factors can affect the adolescent brain - marijuana use included. Further clarity on this subject is sorely needed, given that an astonishing one in three American high-schoolers regularly smoke cannabis.
In the short term, cannabis use can impede concentration, with a number of studies drawing links between cannabis consumption and a higher incidence of fatal car crashes. On top of that, heavy use may be associated with an increased risk of depression, and some studies have suggested long-term effects on cognition, memory and concentration. The Royal College of Psychiatrists has a leaflet that further explores the mental health impacts.
However, it's important to remember that medical and recreational cannabis are two separate issues. Many of the risks discussed are predominantly associated with 'skunk', a form of cannabis with a high THC content that wouldn't be prescribed medically. If medical cannabis were legalised, doctors would be able to prescribe the safest variety for each indication, in the right dosage. And it is likely that certain factors (such as being young or having a family history of schizophrenia) would be classed as a contra-indication.
"I'm not going to say medical cannabis is totally without risks, but personally I think the risks are relatively mild and minimal compared to the benefits, and I would put that ratio very strongly in favour of legalising cannabis medically," says Professor Barnes.
Despite all research conducted to date, there are plenty of gaps in our knowledge. For instance, we don't yet know which forms of cannabis are best for which kinds of pain, and there's a lot more that needs to be understood about the long-term effects on the mind and body. Unfortunately, setting up clinical studies can be a minefield.
"First you have to get a licence from the Home Office, and then you have to get a further licence to get hold of a good grade of cannabis," says Warburton. "Researchers have described a kind of Kafkaesque situation where they would get a Home Office licence but that would run out before they got their cannabis licence, so they'd have to start again. Ironically, opiates like heroin, which is a class A substance and generally considered much more harmful than cannabis, are easier to get hold of for research purposes."
Luckily for the research community, it does seem that change is in the air. According to numerous polls, the majority of people in the UK think medical cannabis should be legalised, which is likely to create a degree of political momentum. Many countries across the world have already taken the jump.
"The World Health Organization (WHO) is currently reviewing its scheduling of cannabis, and members of the Home Office have told our group that they're paying attention to the outcome," says Frank Warburton. "If the WHO changes the schedule of cannabis, the UK may well follow suit."
Barnes agrees that medical cannabis is likely to be legal before too long, pending a change of government.
"The present government is being rather intransigent and they're still saying that cannabis has no medical value," he says. "But pressure is building up, and almost week to week, countries are approving cannabis for medical use. The government can't ignore the fact that very soon it'll be in glorious isolation."
When this will occur, it's difficult to say. But it is clear that this issue will continue to make headlines, with both the benefits and harms perpetually under scrutiny.
Update 31 October 2018: Earlier this month, UK home secretary Sajid Javid announced that medical products derived from cannabis will be available on prescription from 1 November 2018. However, cannabis medicine will only be prescribed by specialist doctors and to patients who have exceptional clinical needs.