There’s been a story making the media rounds lately about a link between weed and schizophrenia. A careful reading of the story sets off alarms about bad journalism and bad science with an agenda, but I’ve been too busy and frazzled to write about it.
Here’s an example from the article linked above….
They said the results mean an estimated 800 cases of
schizophrenia in the United Kingdom could be prevented each year
by ending marijuana consumption.
“We therefore agree with the authors’ conclusion that there
is now sufficient evidence to warn young people that cannabis
use will increase their risk of psychosis later in life,” they
The team did not look directly at people who used marijuana
but instead conducted what is called a meta-analysis by
reviewing 35 studies in search of a potential connection between
psychotic illness and using marijuana
They reviewed evidence from studies ranging from one year to
27 years and only looked at research that did not include people
already showing signs of psychotic illness.
Lots of problems there – it’s a meta-study that ignored important aspects and then pulls the ‘800’ number of their ass.
Here’s a great look from Maia Szalavitz…
Watching the media cover marijuana is fascinating, offering deep insight into conventional wisdom, bias and failure to properly place science in context. The coverage of a new study claiming that marijuana increases the risk of later psychotic illnesses like schizophrenia by 40% displays many of these flaws.
What are the key questions reporters writing about such a study needs to ask? First, can the research prove causality? Most of the reporting here, to its credit, establishes at some point that it cannot, though you have to read pretty far down in some of it to understand this.Second — and this is where virtually all of the coverage falls flat — if marijuana produces what seems like such a large jump in risk for schizophrenia, have schizophrenia rates increased in line with marijuana use rates? A quick search of Medline shows that this is not the case — in fact, as I noted here earlier, some experts think they may actually have fallen. Around the world, roughly 1% of the population has schizophrenia (and another 2% or so have other psychotic disorders), and this proportion doesn’t seem to change much. It is not correlated with population use rates of marijuana.
Since marijuana use rates have skyrocketed since the 1940’s and 50’s, going from single digit percentages of the population trying it to a peak of some 60% of high school seniors trying it in 1979 (stabilizing thereafter at roughly 50% of each high school class), we would expect to see this trend have some visible effect on the prevalence of schizophrenia and other psychoses.