Sex, Drugs and Games

The Psychologists (or psychiatrists)
This is from an edited interview with Dr Robin Murray, Head of Psychiatry at the Institute of Psychiatry London. Psychosis is best defined as a loss of reality, when someone suffers from Psychosis they experience hallucinations, hold delusional beliefs and have disorganised thinking patterns. This can also impact on social interaction, it is said to be a ‘fever’ of mental illness. Psychosis is due to an excess of dopamine in the middle of the brain and we know that if you have an excess of dopamine for any reason this can make people psychotic. Similarly all the drugs that we use to treat psychosis, they decrease dopamine in the mid-sections of the brain. Schizophrenia on the other hand, is a very serious psychosis, and it is for life. 

Dr Robin Murray

What does the dopamine system do?

Well dopamine is the chemical which grabs your attention, so if suddenly something exciting happens, then this is mediated by dopamine, you pay attention to something when dopamine is released. And in psychosis, what people find is that everything seems to catch their attention. A little noise or the way that somebody grimaces or somebody new comes in the door, or they hear something on the television, all of these things seem to be tremendously important and it's because the dopamine makes them important. They think, "Gosh, these are really important to me" and begin to connect them. They think one is connected to the other, they think that television is talking to them, they think the neighbours are conspiring against them. Stick them all together and they develop a sort of delusional explanation that all of these things are happening to me because I am tremendously important, or because the CIA are ganging up against me. And it's the dopamine release that causes people to develop these illusions.


And what role does cannabis play in the dopamine system?

Well the cannabis just revs up the dopamine. We know that from animal studies, there have been fewer human studies, but there are now increasing studies examining that question, exactly what happens when you give cannabis and put somebody in a scanner. Of course this is one of the reasons why cannabis is useful for people with multiple sclerosis or people with chronic pain.

That is to say one of the beneficial effects is the effect of the dopamine and this can help relax some of the muscles of people with neurological disease. So this is one of the reasons why we like taking cannabis, we feel it's therapeutically beneficial. The other function of dopamine of course is that it's a reward chemical, it's a pleasure chemical.

All the drugs that people take, everything from alcohol to cannabis to amphetamines, they all rev up the dopamine system and in most people that just gives pleasure, but some people appear to be vulnerable, that revving up the dopamine system can induce a psychosis.


So the fact that cannabis directly affects the dopamine system suggests to you that it's plausible that it plays a role in psychosis?

Yes.


Some people have compared the influence of cannabis on mental health and the influence of tobacco on lung cancer, do you think that is a fair comparison?

I think it's perhaps more like alcohol actually than smoking, because cigarette smoking account for nearly all of lung cancer, whereas cannabis accounts only for a proportion of schizophrenia. Most people can drink alcohol and they don't get liver failure, they don't become an alcoholic, the more they drink, the more likely they are to develop problems and similarly with cannabis, that most people will get nothing but benefits from smoking cannabis, but a proportion of people will develop problems particularly if they smoke very heavily.