Paranoia. You’re being watched. The people on the street are not who they seem; they’re following you. You’re sure you’ve seen that man before, he must be a spy. It might sound like James Bond’s inner monologue, but these are some of the sensations you can feel while intoxicated after smoking cannabis. They’re also some of the symptoms of psychosis, a disorder of the mind which has been linked to cannabis use. Feeling paranoid when you’re high is not the same as developing a condition like psychosis. The effects of intoxication are gone after a few hours; psychosis as a disorder can involve episodes like this lasting for days, or longer. Currently the government believes that cannabis use as a teenager increases a person’s risk of developing psychosis, but the scientific evidence is not so clear cut.
Although cannabis is illegal, it is a widely used drug. A 2004 report from the European Monitoring Centre for Drugs and Drug Addiction found that two in five 15 year olds in the UK had tried cannabis, and one in ten had done so more than 50 times the previous year. Because of this, you might expect there to be lot of youngsters with psychosis, but it’s a very rare disorder. David Nutt, the ex-government drug advisor, has pointed out that although the use of cannabis has increased dramatically over the last few decades, the number of people with psychosis over the same time period has not increased at the same rate. If there was a direct link between cannabis use and likelihood to develop psychosis, you would expect to see both either increase or decrease together. If there is a link between cannabis use and psychosis it is likely to be complicated, and it is still not clear in which direction an effect occurs. It may be that the link is seen because people with psychosis find that smoking cannabis alleviates some psychotic symptoms, such as social anxiety, so they self medicate.
Epidemiology, the study of population health outcomes, is one of the main methods used for investigating illicit drugs. It is not possible to conduct randomised trials, as it is unethical to give people cannabis to take over long periods of time, so observational designs have been used. Most studies that have been conducted to investigate links between cannabis and psychosis have taken measurements at only a single time point, which means it’s impossible to tell whether cannabis use is causing psychosis, even if there is evidence of an association. In order to avoid this problem, I am lucky enough to be able to use a huge dataset. It’s called Children of the 90s, otherwise known as the Avon Longitudinal Study of Parents and Children (or ALSPAC for short). All pregnant women in Avon whose baby was due between April 1991 and December 1992 were invited to take part in this study. Over 14,000 women agreed, and they and their children have been followed ever since. Lots of information about the mothers and the children has been collected; most years since the study began there have been clinics or questionnaires. These collect information about all sorts of things from emotional wellbeing to blood pressure, plus biological and genetic information on the children and their parents.
I can use the data collected in ALSPAC to investigate whether cannabis and psychosis are linked. The children have been asked regularly throughout their childhood whether they have ever tried cannabis, and also interviewed frequently by psychologists about potential psychotic experiences they may have had, such as hearing voices or feeling they’re being watched. As well as this, information has been collected on a number of other factors that may also influence either psychosis, cannabis use, or both. These can include things like socio-economic status, use of other substances (such as alcohol and tobacco), or family history of psychosis. This means I can account for any effect on the link between cannabis and psychosis caused by these factors, and be more confident that any association I find is due to the factors I am interested in. The genetic information available in ALSPAC will also be useful. Genes can interact with the environment to influence outcomes such as psychosis, so there may be a genetic influence whereby cannabis use will only lead to psychotic outcomes if a certain gene is present.
I am in my first of four years investigating this topic, so I’ve barely begun. But by using this brilliant data set I aim to try and find the direction of any link between cannabis and psychosis, and whether genes are involved in the complex relationship, in the hope that science can give clearer advice to government policy makers in the future.
----------
I wrote this article a couple of months ago, for a science writing prize. Alas it was not shortlisted, but it seems a shame for it to never see the light of day. I post it here in the hope that someone will come along and tear it to shreds, and help me improve my science writing. I'd also love any comments on the content (of course!)
Cheers!
Cheers!
No comments:
Post a Comment