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UK cannabis market dominated by high-potency 'skunk'

(Image: David Potter)

The first comprehensive survey of cannabis strength published in the UK for almost 10 years finds that high-potency varieties made up 94% of police seizures in 2016. The study, co-authored by King’s College London researchers, highlights the potential threat posed to mental health by a market dominated by strong cannabis.

Researchers analysed almost a thousand police seizures of cannabis from London, Kent, Derbyshire, Merseyside and Sussex. The same areas were last sampled in 2005 and 2008.  In 2016, 94% of police seizures were high-potency sinsemilla, also known as ‘skunk’, compared to 85% in 2008 and 51% in 2005.

‘In previous research we have shown that regular users of high-potency cannabis carry the highest risk for psychotic disorders, compared to those who have never used cannabis,’ says senior author Dr Marta Di Forti, MRC Clinician Scientist at King’s College London’s Institute of Psychiatry, Psychology & Neuroscience.

‘The increase of high-potency cannabis on the streets poses a significant hazard to users’ mental health, and reduces their ability to choose more benign types,’ says Dr Di Forti.

The study, published today in the journal Drug Testing and Analysis, found the dominance of sinsemilla was mainly due to a sharp reduction in availability of weaker cannabis resin; from 43% in 2005 and 14% in 2008, to just 6% in 2016 but as low as 1% in the London area.

The average concentration of THC -  the main psychoactive component of cannabis – in resin also increased from 4% to 6%. The average concentration of THC in sinsemilla has remained at 14% between 2005 and 2016.

Historically, cannabis resin has been rich in cannabidiol (CBD), which is almost entirely absent from sinsemilla. Due to its antipsychotic activity, CBD may potentially moderate some of the effects of THC. However, changes in the source of cannabis plants used for resin has led to a drop in CBD content. In 2005 and 2008, the ratio of THC to CBD was 1:1, whereas in 2016 the ratio was 3:1.

A recent King’s College London study found the first evidence for a relationship between increases in cannabis potency and first-time admissions to drug treatment, using data from the Netherlands. The research team are now investigating whether changes to the cannabis market in the UK are having a measurable impact on mental health.

Dr Di Forti, whose research into the mental health impacts of cannabis is funded by the Medical Research Council, says ‘More attention, effort and funding should be given to public education on the different types of street cannabis and their potential hazards. Public education is the most powerful tool to succeed in primary prevention, as the work done on tobacco use has proven.’


Paper reference

Potency of Δ9–tetrahydrocannabinol and other cannabinoids in cannabis in England in 2016: Implications for public health and pharmacology’, Potter et al, Drug Testing and Analysis, DOI: 10.1002/dta.2368



For a copy of the paper, to interview Dr Marta Di Forti or for further media information please contact: Robin Bisson, Senior Press Officer, Institute of Psychiatry, Psychology & Neuroscience, King’s College London, / +44 20 7848 5377 / +44 7718 697176.