May 2, 2007
Huge numbers of news sources are reporting on recent neuroscience studies that have linked the effect of cannabis on the brain to the development of psychosis.
The excitement is because the 2nd International Cannabis and Mental Health Conference is currently under way in London where scientists from around the world are presenting the latest research on the effects of cannabis.
Luckily, the conference programme and summaries for all the research presented are available online as a pdf file, so you can get a more accurate idea of what the studies have found.
However, the main thrust of the news stories is that even a single dose of THC, the main ingredient in cannabis that causes the 'high', can trigger psychotic symptoms.
A study by Dr Cyril D'Souza noted that:
Δ-9-THC produced schizophrenia-like positive and negative symptoms, altered perception, increased anxiety, produced euphoria, disrupted immediate and delayed word recall, impaired performance on tests of attention and working memory without impairing orientation.
The difficulty is that just because something seems to cause similar effects to psychosis, it doesn't necessarily mean it is strongly linked to it.
For example, a dose of alcohol can 'produce' similar symptoms to Alzheimer's disease - loss of memory, disorientation, mood swings, aggression and so on - but that isn't a good basis to say that the alcohol is doing the same thing in the short-term as the degenerative brain disorder does in the long-term.
More convincing are the results from the cognitive tests: impairment in immediate and delayed recall, attention and working memory without impairing orientation.
This is because the subjective effects of both cannabis and psychosis are, well subjective, but the cognitive effects are measurable with controlled neuropsychological tests.
One particularly interesting study from Dr Cecile Henquet found that when compared to controls, patients experienced a greater increase in psychotic experience after taking THC, but also had a greater improvement in their mood.
This might explain why people with psychosis will often continue smoking cannabis even when they know it causes their mental state to deteriorate.
Another fascinating finding, is that as well as containing the possibly psychosis increasing THC, cannabis also seems to contain an antipsychotic called cannabidiol or CBD.
One study presented by Prof Markus Leweke found that purified CBD had a beneficial effect equal to amisulpride, a widely used pharmaceutical antipsychotic medication.
If you're interested in finding out more about the cutting-edge of cannabis research the surprisingly readable conference programme is well worth checking out. Link to conference programme and research summaries.