Cannabis and mental health

Over the past few years, research has strongly suggested that there is a clear link between early cannabis use and later mental health problems in those with a genetic vulnerability - and that there is a particular issue with the use of cannabis by adolescents.

A study following 1600 Australian school-children, aged 14 to 15 for seven years, found that while children who use cannabis regularly have a significantly higher risk of depression, the opposite was not the case - children who already suffered from depression were not more likely than anyone else to use cannabis. However, adolescents who used cannabis daily were five times more likely to develop depression and anxiety in later life.

Three major studies followed large numbers of people over several years, and showed that those people who use cannabis have a higher than average risk of developing schizophrenia. If you start smoking it before the age of 15, you are 4 times more likely to develop a psychotic disorder by the time you are 26. They found no evidence of self-medication. It seemed that, the more cannabis someone used, the more likely they were to develop symptoms.

Why should teenagers be particularly vulnerable to the use of cannabis? No one knows for certain, but it may be something to do with brain development. The brain is still developing in the teenage years – up to the age of around 20, in fact. A massive process of ‘neural pruning’ is going on. This is rather like streamlining a tangled jumble of circuits so they can work more effectively. Any experience, or substance, that affects this process has the potential to produce long-term psychological effects.

Recent research in Europe, and in the UK, has suggested that people who have a family background of mental illness – and so probably have a genetic vulnerability anyway - are more likely to develop schizophrenia if they use cannabis as well.

Recent research in Denmark suggests that yes, there is. It is a short-lived psychotic disorder that seems to be brought on by cannabis use but which subsides fairly quickly once the individual has stopped using it. It's quite unusual though – in the whole of Denmark they found only around 100 new cases per year.

However, they also found that:

**Three quarters had a different psychotic disorder diagnosed within the next year.
**Nearly half still had a psychotic disorder 3 years later.

So, it also seems probable that nearly half of those diagnosed as having cannabis psychosis are actually showing the first signs of a more long-lasting psychotic disorder, such as schizophrenia. It may be this group of people who are particularly vulnerable to the effects of cannabis, and so should probably avoid it in the future.

I would say it's only if you use to too often (all day, perhaps) for a long period of time. Again, it's only anecdotal, but that seems to usually be the case. People just use mental health as an excuse to tell you not to smoke pot, when the truth is, there's nothing wrong with it in moderation.