Opponents of cannabis use have this week seized on the results of a new study in the UK that highlights the dangers of ultra-powerful "skunk" cannabis. The research suggests that skunk users treble their risk of psychosis compared with non-users, and quintuple it if they use skunk daily.
But New Scientist has found that another purified extract of cannabis is showing great promise as a potential drug to prevent or treat psychosis.
What did the skunk study show?
Researchers explored factors affecting psychosis in 410 people diagnosed with the condition for the first time, comparing their lifestyles with those of 370 controls who'd never had psychosis.
They found that psychosis was three times more likely in those who smoked high-potency skunk cannabis, compared with non-users. "In daily users of skunk the risk rose fivefold," says Robin Murray of King's College London, who co-led the team. People who smoked low-potency hash, by contrast, were no more likely to experience psychosis than non-users, suggesting skunk was the culprit.
What is it that makes skunk disproportionately harmful?
Basically, it is far richer than hash in delta-9-tetrahydrocannabinol, or THC, the ingredient that creates the drug's high but which also triggers psychosis. Even more important, skunk contains hardly any of a substance called cannabidiol, or CBD, which has been shown to counteract the psychotic effects of THC. "In traditional hash, the proportions of THC and CBD are about equal, at 4 per cent each," explains Amir Englund of King's College London, who was not involved in the study. "In skunk, THC reaches around 14 to 15 per cent, while CBC tumbles to barely a trace," he says.
How come there's so much THC in skunk?
Both substances are made in the marijuana plant from the same starting material, called cannabigerol, so if the content of one goes up, the other goes down. In hash, typically grown under natural conditions in north Africa, the cannabigerol is converted equally into both.
But producers in the UK have bred strains in which the enzyme for making THC is more dominant, generating cannabis with much higher THC content and much lower CBD content as a result.
Because this type of cannabis is stronger, and more likely to be demanded by regular users who need stronger strains to get their hit, it has come to dominate the black market in the UK over the past 20 years. Hence the increase in psychosis, especially in new, young regular users who have not had time like their older peers to get used to stronger strains. "It's like having a couple of scotch whiskies every day instead of a pint of beer," says Englund.
Is there proof that CBD dampens psychosis?
The evidence is growing, to the point where purified cannabidiol is being tested as a possible treatment for psychosis in people with schizophrenia. A company called GW Pharmaceuticals in Cambridge, UK, is testing it in 80 individuals with schizophrenia split between the UK, Poland and Romania to see if it reduces their risk of psychosis.
Englund and his colleagues published results two years ago in the Journal of Psychopharmacology, DOI: 10.1177/0269881112460109, showing that in 48 healthy volunteers, 42 per cent suffered psychotic episodes following injections of THC, compared with just 14 per cent if they received a tablet of CBD beforehand.
Also, recipients of CBD were less likely to suffer paranoid episodes, and unlike non-recipients, suffered no memory loss on word-recall tests.
Is CBD as effective as existing antipsychotic medicines?
Apparently so. A study in Germany, published two years ago, showed that in 33 patients with schizophrenia, CBD alleviated psychotic symptoms as well as the existing medication, amisulpride, but without the usual side effects, including movement disturbances, weight gain and sexual dysfunction Translational Psychiatry, DOI: 10.1038/tp.2012.15).
That's great, but what can be done now to help users avoid damage from skunk?
Murray favours education, to warn existing and potential users of the risks they face, in the hope that they either give up or failing that switch to hash instead.
David Nutt of Imperial College London, who has argued for decriminalisation of cannabis, believes that skunk would disappear if governments or states made consumption legal by overseeing its production and regulating its sale, supply and content, as is happening in Uruguay and the US state of Colorado. "Prohibition has created the monster of skunk," he says. "The solution is to regulate cannabis trade."
Journal reference: The Lancet Psychiatry, DOI: 10.1016/S2215-0366(14)00117-5.
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