South Londoners who smoke skunk weed – a much more potent strain of cannabis – were found to be three times more likely to register at hospitals with first-episode psychoses, according to a study made by British researchers. The research has many shortcomings though, as is to be expected from a case-control design where it’s always difficult to account for external variables. As the old saying goes, correlation does not equal causation, so take these findings with a grain of salt. The study is valuable however considering it’s among the few which actually considered the relationship between cannabis use and psychosis, often ignored by mainstream cannabis research. Cannabis is used by millions of people worldwide, yet its long-term effects are seriously under reported.

Stinky skunk weed

Credit: Marijuana Venture

Some people might confuse skunk as another slang term for cannabis, when in fact it’s a different strain altogether with much greater potency.  It has around two to three more times of the main active ingredient – tetrahydrocannabinol, or THC. Around 10% of all users will have an unpleasant experience with the drug, according to the Royal College of Psychiatrists. Long-term use of the drug can have a depressant effect, reducing a person’s motivation.

Links between increased incidents of psychosis among skunk users have been reported before, but interpretations have been mixed. Former government adviser Professor David Nutt wrote in 2009 that despite skunk being around for at least a decade, there had been no obvious rise in schizophrenia. In fact, he said, evidence shows psychosis and schizophrenia have been in decline among the British population, despite cannabis being used by a growing number of people over 30 years.

The latest report published in Lancet Psychiatry is based on scientists’ work with 410 patients, aged 18-65, who presented at south London hospitals with a first episode of psychosis. The patients exhibited schizophrenic behaviour such as hearing voices or suffering delusions for at least a month. To compare, the researchers identified a control group of 370 healthy participants from the same area, some of whom also smoked cannabis. They found that those with psychosis were much more likely to have used skunk every day, than to have never used cannabis. Interestingly enough, those who smoked hash every day were no more likely to have psychosis than people who never tried cannabis. Hash is thought of as a ‘cleaner’ cannabis, with around 5% THC, as opposed to 15% THC found in skunk.

Sir Robin Murray, professor of psychiatric research at King’s College London, warned however that the study doesn’t provide a causal link.

“The argument initially was that the people who are going to smoke cannabis are a bit odd anyway,” he said. “In south London, two-thirds of people have used cannabis and it seems unlikely that two-thirds of people are abnormal.”

Skunk and hash use were self-reported in this study, which means researchers had to rely on patients being good judges of how often they smoked, how much and, most importantly, what they smoked. Considering there are all sort of street smokes sold all over South London, like synthetic powerful highs known as “Spice”, the findings become even more controversial. A more refined, close to reality reporting would have been obtained if blood tests and analysis had been made.

Murray doesn’t discount the findings, however, and actually think hash should be recommended to hardcore smokers looking to quit. He likens the experience to alcohol abuse.

“You’re not going to go psychotic after a couple of puffs,” he said. “It’s like alcohol – drinking the odd glass of wine is fine, but if you’re drinking a bottle of whisky a day you’re heading for trouble.”

Some headlines in British newspapers today were in the lines of “one in four of all serious mental disorders caused by skunk”, but sensationalism aside if skunk does indeed cause an increased risk of psychosis, then more efforts should be made considering its widespread use, especially among teenagers. In this respect, the paper does make some steps forward.