00:02In 2011, we conducted a modestly sized study that looked at age of onset of psychosis among
00:09cannabis and non-cannabis users and found an overall two and 2.7 year age gap with an earlier
00:16age of onset among the cannabis users. And since then, there's been this massive increase in the
00:20amount of literature. And we wanted to see whether that literature showed the same thing.
00:26Now, people with psychosis develop that illness at very varying ages. And actually studies of people
00:34with psychosis find whole groups of people with different ages. And what we found contrary to
00:42our expectation was that the biggest age gap was in the studies of older people. So people under 20
00:49who have probably quite a high genetic predisposition to psychosis, cannabis use didn't
00:56make very much difference to their age of onset. People at age 20 to 25, about a year, a bit
01:02over
01:02a year, 25 to 30, 4.4 years, and over six years for an older age group of people over
01:0930. So this
01:12somewhat contradicts the prevailing wisdom that cannabis causes psychosis by affecting the
01:21developing adolescent brain and puts cannabis more in the light of a, you know, cumulative toxin
01:28like alcohol and maybe tobacco and lung cancer looks actually much more like a traditional
01:35harmful compound. Can you explain what cannabis does to a developing brain and how that is
01:42different, if at all, to a developed brain? We don't really know that. What we do know is
01:49that the endocannabinoid system is a complex biological system involving the cannabinoid receptor,
01:55the production of brain derived cannabinoids, and a whole set of enzymes. This system has been
02:03present in all vertebrates for 600 million years. So not just before the cannabis plant
02:10arrived, but before any plant arrived on earth. It's really, really old. And this system in humans
02:15is almost identical in fish. It's amazing. Yeah. So the active ingredient of cannabis is
02:23delta-9-THC. That's the, there are some others, but that's the main one. And it acts like a skeleton
02:29key for the endocannabinoid system. Now the purpose of the endocannabinoid system is to regulate other
02:36neural activity. And we know that from a whole host of things, including experiments with a breed of
02:44mice that don't have the cannabinoid receptor and they're skinny. They're very prone to PTSD and they
02:50have epilepsy. And so it's a really fundamental part of vertebrate biology that is interfered with
02:58if you smoke cannabis. And of course it's neuroregulatory. So while you smoke it, you feel
03:03more regulated, but in the longterm that exposure down regulates the endocannabinoid system, leaving
03:10you with less of that regulation. And one of the results of that less regulation is psychosis
03:15and others are almost certainly depression and anxiety and actually probably a range of other
03:20things. Just on psychosis, for anyone who's not exactly sure what it is, can you explain,
03:26you know, in a very general sense, what psychosis is and how it impacts someone?
03:31It's got three major components. One is perceptual abnormality, so that seeing and hearing things
03:36that aren't present. The second one is a disorder of logical thinking. And the combination, if
03:46you're seeing things and you can't think clearly, will lead you to the third component, which is to
03:50have beliefs that are not correct. So thought disorder, hallucinations and delusions. Now, not
03:57everybody has every single one of those symptoms most prominently, but every patient with psychosis
04:02has some of those. There are some other symptoms as well, but they're the main ones.
04:07So Matthew, what do you hope is done with this research?
04:13So this research is part of, you know, quite a large body of research going on internationally.
04:20In my view, we've got into this very strange situation where the, in a sense, the civil liberties
04:26argument about whether people should be able to use cannabis and how dangerous it is, have
04:32been conflated and resolved in this bizarre way by medicalising cannabis. Two thirds of
04:39people who have medical cannabis were cannabis users beforehand. And the medicalisation of cannabis
04:45has given it a halo. So it makes it much more difficult to talk about its harms. The warnings
04:52on cannabis products are very, very scant. There's never been a public education campaign.
04:57In my view, however, we deal with it legally, we need to inform people about the dangers of
05:05cannabis. And in Australia, that's worked very effectively for nicotine. 14 year olds are much
05:12more likely to have smoked cannabis than they are to use nicotine. I think we need to assume
05:19that people are able to make decisions, but we need to give them the information in order
05:25to let them do that.
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