Science and Life
Runway reveals how pterodactyls land
Stem cell researchers see red
War's end opens up Angolan 'Jurassic Park'
Not all alcoholic drinks are the same
Fewer mosquitoes may be a bad thing
Prehistoric tail swingers had sweet spot
Astronomers bust star ratio myth
Sun causes 'La Nina-like effect' on earth
Three genes key to most dog hair types
Manure major source of greenhouse gas
Nanoparticle test may detect lung cancer
Pulsar burns longest ever cosmic trail
Mysterious weather pulses fuel cyclones
Technology makes valuing opals easier
Doubt cast on cannabis, schizophrenia link
Whistling feathers sound predator alarm
Climate may need emergency fix: report
Africa tops climate change risk list
Mesozoic 'Giraffe' unearthed in China
Cannibalism feeds galactic growth
'Climate' genes leave species vulnerable
'Thunder thighs' protect your heart: study
Daylight saving 'causes more accidents'
One-sided animals more successful
  Doubt cast on cannabis, schizophrenia link
A new study in the UK has cast doubt on the supposed link between cannabis use and schizophrenia.

But at least one Australian researcher says the study needs more evidence.

Previous research has suggested cannabis use increases the risk of being diagnosed with schizophrenia or other psychotic disorders.

This latest study, led by Dr Martin Frisher of Keele University, examined the records of 600,000 patients aged between 16 and 44, but failed to find a similar link.

"An important limitation of many studies is that they have failed to distinguish the direction of association between cannabis use and psychosis," the authors write in the latest edition of the journal Schizophrenia Research.

They point out that "although using cannabis is associated with a greater risk of developing psychosis, there is also evidence of increased cannabis use following psychosis onset."
Not as predicted

Frisher and colleagues compared the trends of cannabis use with general practitioner records of schizophrenia.

They argue if cannabis use does cause schizophrenia, then an increase in cannabis use should be followed by an increase in the incidence of schizophrenia.

According to the study, cannabis use in the UK between 1972 and 2002 has increased four-fold in the general population, and 18-fold among under-18s.

Based on the literature supporting the link, the authors argue that this should be followed by an increase in schizophrenia incidence of 29% between 1990 and 2010.

But the researchers found no increase in the diagnosis of schizophrenia or other psychotic disorders during that period. In fact some of the data suggested the incidence of these conditions had decreased.

"This study does not therefore support the specific causal link between cannabis use and the incidence of psychotic disorders," the authors say. "This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence."
More evidence

Professor Joseph Rey of the Faculty of Medicine at the University of Sydney, whose previous research has identified a link between cannabis and schizophrenia, is sceptical of the study's results.

"Not showing that there is a link does not mean there is no link," he says.

Rey says that there may be other factors at play that have reduced the overall incidence of diagnosed schizophrenia.

"The evidence suggesting that cannabis use does increase the risk of schizophrenia is quite strong."

The authors of the study say that while they cannot completely dismiss all alternative explanations of their data, such explanations "do not appear to be plausible".
Echidna ancestors swam with platypuses
Volleyball middle players jump to the max
Roaches hold their breath to stay alive
Suspected Trojan war-era couple found
Dust storm born out of flooding rains
Droughts and flooding rains to intensify
Gene study reveals Indian origins
Malaria drugs may get new lease of life
HIV vaccine breakthrough 'gives hope'
Anglo-Saxon treasure trove unearthed
Cold Aussie dinos hid underground
Sichuan quake once-in-4000-year event
Stem cells point to space ills
Viking 2 came close to finding H2O
Working mums' kids less healthy
Komodo dragon had Australian origins
Bacteria engineered to draw pictures
Samoan tsunami caused by 'shallow quake'
'Academic doping' set to rise: expert
Bird disease struck down T. rex
Mini sats to improve Earth observation
Oldest human ancestor unveiled
Amber gives clues to origin of flowers
Fungus feasted on mass extinction
New disease identified in pet turtles
Brittle bone genes revealed
Pioneers of light win physics Nobel
Antioxidants may raise diabetes risk
Astronomers get neutron star's measure
Bioprospecting needs ecologists: expert
Saturated fats linked to Alzheimer's
Gecko tails dance to their own tune
Cartoons set chimps yawning
Virus may cause prostate cancer: study
Researchers perfect quantum memory
Australian lacewings build toughest silk
NO enzymes help bacteria resist antibiotics
Hikers' socks give weeds a free ride
Migrating birds chill to conserve energy
Borders tell tales on land management
Forget foreplay, size does matter: study
Shower heads home to nasty microbes
Saturn home to the perfect storm
Crazy ants upsetting island ecosystem
New call for e-waste controls
Gene tech helps dandelions ooze rubber
New insights into Greenland icesheet
Mini T. rex ancestor found in China
Rare meteorite find in Australian outback
Scientists uncover how bugs evade capture
World's deltas subsiding, says study
'Quiet' Sun continues to affect Earth