Super-strength 'skunk' cannabis linked to psychosis

“‘Skunk-like cannabis’ increases risk of psychosis, study suggests,” BBC News reports after a new study found high-potency strains of “skunk” cannabis – infamous for both its strength and its pungent smell – could be linked to one in four cases of new-onset psychosis. Psychosis is a mental health condition characterised by symptoms such as hallucinations and delusions.

The study compared cannabis use patterns among 410 people from south London who attended hospital with a first episode of psychosis, and 370 people from the general population without the condition.

It found the daily use of cannabis was associated with an increased risk of psychosis, and use of high-potency cannabis was associated with a greater increase in risk.

The researchers used their figures to estimate that 24% of new psychosis cases in the study population could be attributed to the use of skunk. But it’s important to note this figure would not apply to populations where skunk use is less common than in the south London population the study looked at.

The figure also assumes that skunk definitely directly causes psychosis, which this study cannot prove by itself. However, there is growing concern that this could be the case, and other studies also support an association between cannabis use and psychosis.

If you are troubled by symptoms such as paranoia, depression and anxiety, and are concerned about your cannabis use, ask your GP for advice.

Where did the story come from?

The study was carried out by researchers from King’s College London and Mount Sinai School of Medicine in the US.

It was funded by the UK National Institute of Health Research, the South London and Maudsley NHS Foundation Trust, the Institute of Psychiatry at King’s College London, the Psychiatry Research Trust, the Maudsley Charity Research Fund, and the European Community’s Seventh Framework Programme.

The study was published in the peer-reviewed medical journal, Lancet Psychiatry. It has been published on an open-access basis, so it is available online to download (PDF, 439kb) for free.

The Daily Telegraph is just of one of many media sources to make the mistake of extrapolating the “24% of first-episode psychosis caused by high potency cannabis” figure to the whole of Britain.

In fact, this figure is based on the high levels seen in south London in this study. It is also an estimate based on the assumption that skunk definitely causes psychosis, and that no other confounding factors are having an effect.

Links To The Headlines

‘Skunk-like cannabis’ increases risk of psychosis, study suggests. BBC News, February 16 2015

Super strong cannabis responsible for quarter of new psychosis cases. The Daily Telegraph, February 15 2015

Smoking skunk cannabis triples risk of a serious psychotic episode, says research. The Guardian, February 16 2015

Almost a quarter of new psychosis cases linked to strong ‘skunk like’ cannabis. The Independent, February 15 2015

Strong cannabis causes one in four cases of psychosis: Users three times more likely to have an episode than those who have never tried it. Daily Mail, February 16 2015

Cannabis responsible for quarter of new psychosis cases, scientists warn. Daily Mirror, February 16 2015

Potent Cannabis Linked To Psychosis Cases. Sky News, February 16 2015

Peril of ‘skunk’ cannabis: Drug could be responsible for paranoia and schizophrenia. Daily Express, February 16 2015

Links To Science

Di Forti M, Marconi A, Carra E, et al. Proportion of patients in south London with first-episode psychosis attributable to use of high-potency cannabis: a case-control study (PDF, 439kb). Lancet Psychiatry. Published online February 16 2015