01/25/2014 06:25 EST | Updated 03/27/2014 05:59 EDT

Why Smoking 'Skunk' Cannabis May Lead to Early Psychosis

A recent study published in Schizophrenia Bulletin suggests that daily use of high-potency cannabis can lead to chronic users experiencing their first psychotic episode earlier than they otherwise would. A team of researchers led by Dr. Maria Di Forti at the Institute of Psychiatry at King's College in London surveyed 410 patients between the ages of 18 and 65, all of whom had a history of psychotic episodes. The survey examined history of drug, alcohol, and tobacco use as well as the age at which the patients first experienced a psychotic episode.

What the researchers found was that males were more likely to use cannabis overall than females and also experienced psychosis at a younger age. They also found that patients who started smoking cannabis at age 15 or younger preferred to smoke high-potency "skunk" cannabis rather than lower potency "hash" type cannabis. The earliest onset of psychotic episodes occurred in males who have been smoking high-potency cannabis on a daily basis -- on average, their first psychotic episode occurred six years earlier than for non-users.

Skunk cannabis has become increasingly popular in recent years with a THC content of 16 percent compared to the 4 per cent found in lower-potency "hash-type" cannabis. Though news reports have raised concerns about the dangers associated with skunk cannabis, including people being admitted to hospitals for mental health problems, skeptics have disputed the potential risks involved. Believed to have originated in the United States, European growers have developed a profitable business growing skunk cannabis in hothouses. Users often regard it as being safer than than regular marijuana because it is harder to fake but long-term use of skunk cannabis has been linked to adverse psychiatric effects including depression.

While previous research has attempted to link psychotic symptoms to cannabis use, the findings have often been controversial. Some researchers have raised concerns about cannabis triggering psychosis in some people who are more vulnerable due to family history of mental illness or other factors. In describing the results of this new study, Dr. Di Forti stresses that the findings should not be misinterpreted. "This is not a study about the association between cannabis and psychosis, but about the association between specific patterns of cannabis use... and an earlier onset of psychotic disorders," she told reporters. It is also still uncertain whether the earlier use of cannabis contributes to developing psychotic symptoms or whether people more prone to psychosis prefer to use cannabis as a form of self-medication to control mental health problems.

Dr. Di Forti also stresses that it is still unclear whether there are safe levels of cannabis use. "We know for instance that alcohol can be highly toxic or damaging in the long term to health but that sensible use of it causes no harm. We do not yet know enough about safe use of cannabis and more research is needed," she said. Young people smoking cannabis need to be aware of the potential risks involved and use their own best judgment about how to use cannabis sensibly.

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