But people who used low-potency (“hash”) cannabis – even daily – had no increased likelihood of psychotic disorders compared.

This is according to a six-year study conducted in south London, recently published in The Lancet Psychiatry medical journal.

Between 2006 and 2011, Dr Marti di Forti and colleagues interviewed 410 people who had been admitted to psychiatric facilities after their first episode of psychosis.

They also recruited a control group made up of 390 people of similar ages, ethnic backgrounds and employment status from the same area, who had no history of psychosis.

Over 60 percent of both groups reported some cannabis use – but those in the control group were more likely to be occasional users of low-potency cannabis (hash), while the patients with first-episode psychosis were more likely to be daily users of high-potency cannabis, often called “skunk.”[quote float= right]”The presence of cannabidiol might explain our results, which showed that hash users do not have any increase in risk of psychotic disorders”

Said to be a hybrid of two types of marijuana plants, skunk is considered to be much more potent than common varieties of dagga and is characterised by its strong smell, according to the UK-based non-profit independent centre of expertise on drugs and drug use, DrugScope. People who started using cannabis under the age of 15 year had “modestly, but significantly, increased risk of psychotic disorders”, according to the study.

“Compared with those who never used cannabis, people who mostly used skunk were nearly twice as likely to be diagnosed with a psychotic disorder if they used it less than once a week, almost three times as likely if they used it at weekends and more than five times as likely if they were daily users,” according to the study.

Chemical differences may explain risk

According to the researchers, skunk contained more of the chemical compound, tetrahydrocannabinol (THC) than did samples of hash, and virtually no cannabidiol, another compound in cannabis. There is some evidence that cannabidiol might have anti-psychotic properties, acting to reduce hallucinations.

“The presence of cannabidiol might explain our results, which showed that hash users do not have any increase in risk of psychotic disorders compared with non-users, irrespective of their frequency of use,” according to the researchers.

South London has one of the highest recorded incidence rates of psychosis in the UK, and the incidence of schizophrenia had doubled since 1965.

The study comes about a month after some South Africans asked President Jacob Zuma to legalise dagga after the Presidency invited suggestions for Zuma’s State of the Nation address via Twitter.

Inkatha Freedom Party MP Mario Oriani-Ambrosini asked Zuma to legalise the use of medical marijuana for cancer patients. Diagnosed with lung cancer in 2013, Oriani-Ambrosini died just two months later. – Health-e News.

• Read more: Is there a place for dagga in medicine?