英語語言學習：大麻的藥用價值

Norman Swan: Hello, and welcome to the Health Report with me, Norman Swan. Today, your heart and your genes. Most people think of congenital heart disease as heart abnormalities which affect babies. But in fact it's a bigger problem for adults and many issues don't emerge till you're older. A fascinating study using massive data to do some genetic detective work.

Plus, speaking of detective work, a map of autism spectrum disorder in children which tells us a lot about genes and the environment.

And cannabis and the push to have it legalised for medical uses. It's got the support of the Prime Minister and most states and NSW is leading a trial.

Given all the advocacy going on you'd think that there's heaps of evidence that cannabis works for things like pain and nausea, but a recent review suggests that may not be the case. One of the authors is Professor Mike Farrell who's director of the National Drug and Alcohol Research Centre at the University of NSW, and he's with me in the studio now. Welcome to the Health Report.

Michael Farrell: Hello.

Norman Swan: What worries you about this, Michael?

Michael Farrell: Well, I think what we need to do is we need a balanced and measured approach to the evidence around treatment efficacy. So one of the things that worries me is when we've got this discussion that we are not actually looking hard enough at the evidence. One of the problems is that some of these conditions are hard to research and measure, for instance pain is a very subjective thing, so actually getting very good measures of pain and understanding where the effects are can be quite complicated.

Norman Swan: I mean, we haven't even studied Panadol properly.

Michael Farrell: We have all sorts of problems with chronic pain, even understanding the nature of pain and why we should medicate it or what we should do and what's best is a very broad discussion.

Norman Swan: So let's go through the evidence and let's start with pain. What is the evidence that cannabis has any effect on pain?

Michael Farrell: Well, the evidence is conflictual. There are a number of studies that show positive effects and there's a number of studies that show really…if you want to summarise it, the evidence at the moment is quite modest for pain. Probably the best evidence is around multiple sclerosis and using it for spasm and some of the spasm pain in multiple sclerosis, and that's where the cannabis type medications have in quite a number of countries been authorised for medical use.

Norman Swan: A lot of people don't realise there have been cannabis type medications authorised for use for over 30 years. The United States has got one and Europe and Britain have got others. We don't have any here I don't think.

Michael Farrell: No, dronabinol has never really…which was one of the first ones to be a synthetic cannabinoid that was authorised, but it has never really been put to great use, it has never been shown to be…whereas some of the newer ones like nabiximol which is actually derived directly from the plant THC and CBD is probably more user-friendly and more acceptable from a patient user point of view.

Norman Swan: So that's pain. The jury is out on pain. It doesn't look as if…if there is an effect it's going to be relatively small. What about nausea and vomiting? Because I think that was the first indication for cannabis or a cannabis derived compound almost 30 years ago.

Michael Farrell: That's right, and that's where dronabinol and these ones came in. One of the complexities of it is when you look…you are actually not just looking for efficacy, you are looking at comparative efficacy. And some of the other medication for nausea in the cancer field has come on in great leaps and bounds in the last 30 years, so actually it's putting really cannabis on the back foot from that point of view…

Norman Swan: Meaning they are more effective with fewer side effects.

Michael Farrell: Yes, that's one of the issues, is that you are having more effective medications. So from that point of view where cannabis now fits in in comparison to years ago is far more…again the jury is out on it.

Norman Swan: Another area of use, because you get the munchies, proverbially, if you smoke marijuana or consume marijuana therefore you eat more, was appetite stimulation, particularly in weight loss conditions like when you've got established AIDS.

Michael Farrell: Yes, and there was great interest in that and there's been a number of studies done, but of course it is again confounded by the introduction of AZT, which is actually a very effective treatment for HIV.

Norman Swan: So when the antiretrovirals came in, people put on weight.

Michael Farrell: That's right, so then the potential role of something like cannabis really moved into the back seat, and there hasn't been a lot more work advanced on it, primarily because of the effectiveness of AZT.

Norman Swan: What other uses to which has it been put?

Michael Farrell: Well, there's discussion about, for instance might it be used in dementia for cognitive protection. There is no great evidence that it does that but…

Norman Swan: I thought it caused cognitive decline.

Michael Farrell: Well, that's what some people would think, but then other people are arguing that maybe the CBD component might be neuroprotective.

Norman Swan: CBD?

Michael Farrell: It's the other component besides THC of cannabis, and it's the one that doesn't actually have psychotic properties, so there's a lot of interest in it.

Norman Swan: We'll come to side-effects in a moment, but some of the people who say, well, you know the evidence isn't strong because you're testing the wrong compound, and if you smoke cannabis then you are getting the whole natural compound and the things that work, whereas when you synthesise it you are not necessarily getting the things that work.

Michael Farrell: Yes, that's where the THC and CBD, the medications derived from the plants themselves, may have a benefit, but it has to be said that there are studies and…

Norman Swan: Well, people say the other way around, that smoking has more benefit than synthetic…

Michael Farrell: Well, they do, but there's one very authoritative systematic review just published as the American College of Pain Guidelines, and basically…smoked cannabis comes out worse of all the different varieties in relation to evidence for benefit.

Norman Swan: Even with its powerful placebo effect? Because obviously there is a huge placebo in the whole business of taking it.

Michael Farrell: Well, I suspect that may be different for people with…one of the things we probably need to distinguish is people who have had experience taking cannabis as compared to people who would be taking cannabis for the first time as a medication.

Norman Swan: So what are the issues around that?

Michael Farrell: Well, the issues around that are the psychoactive effects, you know, that somebody who has acquainted themselves with cannabis may see as desirable, but if you've never had them you may not actually want any of these psychoactive effects, and that you may experience them as very unpleasant and adverse. And that could be either a slight euphoria, it could be anxiety, or it could be nausea even. You know, there's a range of different things. Or it could be more a sense of derealisation. There's a range of effects that you can have with cannabis.

Norman Swan: So what’s the risk of psychosis if you're 65, you are told you've got a year to live with your cancer and you think, what the heck, I'm going to take cannabis?

Michael Farrell: That's probably way down the list of risks from that point of view. The risk is pretty…the risk of psychosis with cannabis we know is pretty modest anyway. It's not so modest if you actually have a strong family history of psychosis, but without that the risk is pretty modest. You're probably more concerned about other side-effects, like anxiety, mood disorders and potentially getting subjective effects, that you feel out of control, and they're just decidedly unpleasant unless you've had previous experience.

Norman Swan: One thing I was wondering about is you get this amotivational syndrome where you are not really motivated to do stuff, whether that's an adolescent issue in cannabis I don't know, but whether or not you…you know, if you're undergoing cancer care and you start smoking dope, whether you think, oh well, I don't really need to have my chemo anymore, and you could be denying yourself treatment.

Michael Farrell: Well, one of the concerns around people using it for MS is that it may be associated with cognitive decline in MS. So that's one of the potential adverse effects of using it with MS. But that has to be offset with the benefits of pain and spasm reduction.

Norman Swan: And if you're 40 and got chronic pain and you are going to be taking it long-term, and smoking it, what are the risks to your lungs?

Michael Farrell: Well, at 40 probably modest. You may not have to smoke it. There are…you could take nabiximols, like what we call Sativex, which is now licensed in Australia, it's primarily licensed for multiple sclerosis, but there may be the opportunity to use it off-licence for particular individuals. And I think the risks are far more around anxiety, mood disorders and the more common mental disorders and other subjective side-effects rather than psychosis or that.

Norman Swan: So New South Wales is leading a trial for the other state governments. I think the ACT has come on board, Victoria is supportive, and I think people at Monash University are advising on this trial. Is it going to answer any questions in terms of how well it works?

Michael Farrell: Well, it possibly could. The message we think clearly is that we need more research to see where the efficacy lies, and if well designed trials are put in place, along with other international trials that are rigorous and really properly…modern designed trials, they will add to the body of evidence. And one of the things we need is a good body of evidence so that we've got less of this sort of either exaggerated claims of benefit or exaggerated negative claims about the harmful effects, and just trying to find a real middle way between that.

Norman Swan: Now, just signalling that I'm going to be talking about this on the Health Report today I've already got my email bag and people are saying I'm just a tool of the pharmaceutical industry, this is a plot to deny people a natural medication that's going to help them enormously.

Michael Farrell: Well, the complication of it is what is a natural product that can be consumed for recreational purposes and what then is an agent, a medication with defined efficacy, are two different questions. So people wishing to use this as adjunctive usage for subjective sense of betterment is one thing, but actually it being a clearly defined therapeutic agent needs far closer scrutiny before those claims can be made.

Norman Swan: So beware of the bandwagon. Michael Farrell, thank you very much indeed.

Michael Farrell: Thank you.

Norman Swan: Mike Farrell is director of the National Drug and Alcohol Research Centre at the University of NSW.