Cannabis

But first a literal translation of a pictorial joke - Two men standing at a bar waist-deep in water. One turns to the other and says "I feel sorry for all those smokers; it must be cold outside"


Right the Lancet has/will published a report that takes the result of 35 studies into account regarding cannabis. The results being reported and interpreted by GMTV and the BBC news this morning.

Smoking just one joint doubles your risk of having a psychotic episode later in life to over 40%! So taking that as read the default possibility of having a psychotic episode is 20%? That's 1 in 5 people, could be true but seems a little high to me. Ah but check the fine print "vulnerable people".

So that's people who already have an above average chance of a psychotic episode are more likely to have one if they smoke cannabis and the chances increase the more they smoke. Okay what's the percentage of the population deemed vulnerable? Not reported.

Then we turn to the BBC who posts a figure of 41% (over 40%), but states this as an increase of not to. Now an increase of 41% isn't doubling the risk, so we're either dealing with two different figures or someone's got something wrong.

If in doubt turn to the written word and the BBC report in full Ah yes here we are - the two figures are separate. Cannabis users are 40% more likely then non-users to have a problem, no wait the most frequent users have twice the risk of non-users. What? So one puff increases the risk by 40%, but lots increase it by 100%? Ah look closely:

Cannabis users are 40% more likely than non-users to suffer a psychotic illness... the most frequent users of cannabis have twice the risk of non-users of developing psychotic symptoms...

my emphasis. Yep two different things. So again what are the base figures we're working with? What a surprise not mentioned. Is this important; well yes.

Imagine the average risk of developing a psychotic illness was 1% an increase of 40% results in (not 41%) 1.4%; For that 'twice the risk' for symptoms 1% becomes 2%. So if you were told that doing something increased the risk by 0.4% or 1% would you say "Oo no that's become way too risky now"?

Now if the base was 50% then we're looking at 70% and 100% respectively, now that's a jump that might give you pause. How do you know we're more in the 1% range then the 50% range

The authors said the risk to any individual of getting schizophrenia remained low overall...

Wait there's another damaging statistic

"...estimated it could be a factor in 14% of psychotic problems among young adults in the UK."

Okay that is something to look at (as a comparison it's about the same percentage as ascribed to drink-related road deaths) except it's an estimate. You can't split the world into two and watch the same person with and without cannabis in fact

"Their prediction that 14% of psychotic outcomes in young adults in the UK may be due to cannabis use is not supported by the fact that the incidence of schizophrenia has not shown any significant change in the past 30 years."

and that's taking into account the increase in strength of such drugs over the years.

Hold on though wasn't there a Commons report in February that stated it wasn't a sufficient cause oh yes I mentioned it myself. Now of course science is about re-examining data and theory so just because an earlier report said it wasn't that bad doesn't mean we should take the later report as wrong (or right), but it does pose the question about why they differ.

Finally just to prove that the authors really are trying to look at the entire situation

"It is possible that the people who use cannabis might have other characteristics that themselves increase risk of psychotic illness."

In other words maybe only crazy people smoke cannabis. ;-)