A new study has proved that smoking potent ‘skunk-like’ cannabis increases your risk of serious mental illness. Around one in 10 new cases of psychosis is estimated to be associated with strong cannabis use.

The researchers, from King’s College London, investigated cannabis use by people in 11 EU towns and cities and one region of Brazil. They then compared 901 people who had experienced psychosis with 1237 (from the general population) who had not.

The type of cannabis used by participants was categorised according to strength. Low potency cannabis was any product thought to contain less than 10% concentration of Δ9-tetrahydrocannabinol (THC). This is the psychoactive component of the cannabis drug, which gives users the ‘high’ feeling. High potency cannabis was categorised as anything containing more than 10% THC. However, no lab tests were undertaken to measure the cannabis strength directly.

Cannabis and psychosis link

The results showed that people who used cannabis on a daily basis were three times more likely to have a diagnosis of first episode psychosis, compared with people who had never used cannabis. This increased to five times more likely for daily use of high potency cannabis. There was no evidence of an association between less than-weekly cannabis use and psychosis, regardless of potency.

The authors estimate that one in five new cases of psychosis across the 11 sites may be linked to daily cannabis use, and one in 10 linked to use of high potency cannabis. In London and Amsterdam, where most of the strong cannabis is sold, the risk could be much higher, report the researchers in The Lancet Psychiatry. Experts estimate that skunk-like cannabis with a THC content of 14% now makes up 94% of the drug sold in London.

Lead researcher and psychiatrist Dr Marta Di Forti said: “If you decide to use high potency cannabis bear in mind there is this potential risk”.

People experiencing psychosis lose touch with reality. They may hear voices, see things that are not actually there or have confused, delusional thoughts. Researchers from the UK and Canada have also found robust evidence to show that using the drug in adolescence can increase the risk of developing depression in adulthood by 37%. However, there is disagreement as to what extent cannabis might cause or worsen mental health problems. Many countries have legalised or decriminalised cannabis use.

Nick Hickmott from the drug and alcohol charity Addaction agreed that the UK had a problem with potency and advised users to avoid high-strength cannabis every day. “People who regularly take lots of high strength cannabis are at risk of potentially serious harm. It can be particularly harmful for younger, developing brains”, he said.

“It’s also important not to over-react. Lots of people experiment with cannabis and then move on without any problems. For people who do need advice or help I’d recommend reaching out to a GP or a local drug service.” For information on any of AlphaBiolabs’ drug testing solutions, please call 0333 600 1300 or email us at