What are the effects of medicinal cannabis?

There is such a mismatch between the law and the scientific evidence. But what does the science say about the effects of cannabis? To find out, Chris Smith was joined by Harry Sumnall, Professor of substance use at Liverpool John Moores University...

Harry - Well, as you mentioned in your intro to this piece, cannabis itself is a very complex plant and it contains hundreds of different chemicals, mostly notably the cannabinoids. You’ve already spoken and CBD and THC which are the cannabinoids that most people are familiar with if they know anything about cannabis. But cannabis also contains lots of other chemicals as well, so other cannabinoids, CBG, THCA, CBN. the list is almost endless. But there are also aromatic chemicals as well called terpenes and this gives cannabis its distinctive smell. But when we think about whether it’s the recreational use of cannabis or the therapeutic effects, most of the focus has been on CBD and THC.

Interestly, the body has its own cannabinoid system. And actually, one of the first endogenous cannabinoids, the body’s own cannabinoids was a drug called anandamide, which is derived from the Sanskrit word for joy and bliss which is rather appropriate.

But the body has two main sets of receptors and these are these chemical locks which cannabinoids and other chemicals act upon. There’s the CB1 receptors and these are located in the central nervous system, and these control functions such as pain, memory, appetite, and even muscle tone as well. There’s another set of cannabinoid receptors - the CB2 receptors - and these are in the periphery, and even in some cells associated with the immune system.

So going back to those two chemicals, THC and CBD, THC acts in the central nervous system and therefore has profound effects on neuronal function, and perception, and all those other functions that I mentioned. CBD doesn’t have a psychoactive effect because it’s acting at CB2 receptors. And, interestingly, this is why CBD is not controlled under the Misuse of Drugs Act which Gary was just talking about.

Chris - And that’s why you can buy it in health food stores, for example. So, basically, what you’re saying is you have in your body a system of communication between cells, including brain cells, which have on their surfaces these receptors or docking stations that these chemicals bind to, and cannabis subverts the system we have naturally in place? It triggers it artificially which is why it then produces these effects?

Harry - That’s right. And we know a bit about THC pharmacology so it has direct pharmacological effects. We know less about CBD. It doesn’t seem to have this direct affect on those receptors, but it may seek to modulate the function of other hormones and neurotransmitters as well. We’re finding a lot more about it.

Chris - Does it matter how you take the drug into your body? Because, obviously, there are a range of different routes in. You could eat this for example. You could swallow the oil that people are talking about. Some people also smoke these drugs. So does it matter how you take it?

Harry - Yeah. Route of administration is very important. So lots of routes of administration, so if you smoke it, it’s inhaled, it’s absorbed through the lungs, you feel the effects within a few minutes. If you eat a cannabis product it needs to be absorbed through the gut and then get into the bloodstream to the brain, and that can take half an hour or an hour.

Anecdotally, some patients also report people who are using it for medicinal purposes, the different routes of administration also have subtly different medicinal effects as well, but that is largely anecdotal.

Chris - When we’re talking about things like relief of pain and so on, do we know which of these different systems, the central nervous system or the peripheral effects are most important in achieving those benefits?

Harry - We think for pain relief, then the CB1 system is primarily important there because they are receptor sites, these locks, which are directly located in the central nervous system. There’s lots of interest in the use of cannabinoids and cannabis derived medicines for treatment of epilepsy for example. Now some of the effective drugs that we have there are working on the CB2 system which are outside of the central nervous system and, therefore, they’re having some novel and unusual effects which you wouldn’t usually associate with anticonvulsants that are usually prescribed.

Chris - We’ve dwelled very much on the medical side of this, Harry, but what about the psychological and emotional consequences of people using things like cannabis?

Harry - We know a lot about the potential negative effects of so-called recreational cannabis use. If we’re thinking about what the potential negative effects of medicinal use are, then there is already a body of knowledge there. I think it’s quite important to separate some of those harmful effects with recreational use from medically supervised use.

A lot has been discussed popularly about mental health impact of cannabis, and I think sometimes there’s a tendency to completely discount the mental health effects. But there is some good evidence to show that the particularly high risk individuals, maybe individuals who've had a greater susceptibility to psychosis, for example, that are regularly using cannabis in whatever form, whether that’s oral, whether that’s smoking, is not a good idea. And regularly using cannabis, particularly at early ages, can increase the risks of experiencing psychotic symptomatology.

克里斯,但有些人认为,哈利,对不起terrupt - that people who are at risk of developing those conditions are just self-medicating, and they’re taking the cannabis because they’re beginning to experience mental ill health and it makes them feel better, rather than the cannabis comes first and causes the mental ill health downstream?

Harry - I think there’s probably a lot of truth in that perception. We do know that from some of the surveys and studies that have been done that when particularly young people in their early teens, when they begin to experience some of these symptoms, unusual symptoms, they do report that smoking cannabis can actually make them feel “normal.”

There’s also some interesting research which also suggests that even the tobacco that people mix cannabis with in this country in joints might also increase the risk of psychotic symptomatology. So I think the exact mechanisms are unclear, but I think there’s a very simple public health message, particularly for young people, is to delay use of cannabis and also to reduce frequency of use as well. Regularly using cannabis is not good for your mental health.

Chris - So far we’ve talked about side effects in one particular tissue - brain tissue. If you’ve got this wide distribution of receptors all round the body, are there side effects in other organs and tissues and, therefore, would a person experience things other than just maybe mental ill health if they abused cannabis?

哈利,我想我们做诚实的答案n’t quite know. If we look at the some of the clinical studies which have been undertaken with some of the pharmaceutical preparations then patients do report side effects. These can be side effects related to some of the psychoactive effects, so confusion, many memory problems, or excess sleepiness. But then also some patients are reporting physiological side effects as well, gastric disturbances for example. So the potential is there, but I think we don’t know a lot about this and how counter this because we know so little about how cannabis related products are actually working, so we don’t know a huge amount about the pharmacology.