Marijuana. Picture: ISTOCK
Marijuana. Picture: ISTOCK

"Cannabis does not cause schizophrenia." This is the conclusion of Prof David Nutt‚ psychiatrist‚ neurologist and director of the neuro-psychopharmacology unit at London’s Imperial College.

Nutt is testifying in the High Court in Pretoria in a civil case brought by Johannesburg residents Myrtle Clarke and Jules Stobbs. The pair‚ nicknamed "the Dagga Couple"‚ are asking to have the laws banning dagga repealed and sent to Parliament to be reworked.

Nutt is world-famous for his work comparing the harms of 20 drugs and rating drugs by their level of harm‚ with the findings published in a 2009 article in The Lancet medical journal. He was also fired by the UK government where he worked in drug policy‚ after publishing that taking ecstasy was much safer than horse-riding.

Nutt has studied dagga’s links to schizophrenia‚ as this alleged link is often cited by governments as a reason to keep it illegal. In a 30-year period from 1970‚ dagga use in the UK increased by 20% he told the court. If it caused schizophrenia‚ Nutt said, he expected the rise in cannabis use to mirror an increase in cases of the disease in the country, which did not happen.

"This shows cannabis cannot cause schizophrenia. Schizophrenia is a very rare disease," Nutt admitted, though, that dagga use can lead to temporary psychotic symptoms.

A state witness‚ Harvard medical Prof Bertha Madras, who will testify on paper for the government‚ says dagga use leads to an earlier onset of schizophrenia‚ which usually first appears in a person’s 20s. Doctors for Life will also testify that dagga is linked to schizophrenia.

Nutt also told the court that "cannabis cannot kill‚ whether smoked or eaten‚ whereas alcohol does". "Three people a week die in the UK from alcohol related harms‚" he said. "Very few people will die from cannabis‚ whereas 8,000 people die from alcohol use a year in the UK."

He said other research showed that 9% of cannabis users became dependent on it‚ but 12% of people who used alcohol became addicted. Nutt also said that data showed legalising dagga did not increase road accidents‚ which is often a concern for governments. This concern was one of the reasons the UK would not legalise dagga‚ he said.

Data showed since legalising dagga in Colorado in the US‚ traffic accidents from alcohol decreased. This is because people were switching from drinking to using cannabis‚ he explained. Driving "stoned" doubled the likelihood of an accident; alcohol use made a car accident eight times more likely.

He also said cannabis prohibition in UK had led to people searching for "so-called legal highs" by using artificial cannabinoids. These products are similar chemically to dagga but are "undetectable‚ much stronger and riskier‚" Nutt said.

He compared the prohibition of marijuana to alcohol prohibition in the US in the 1930s‚ that led to the consumption of unregulated and more dangerous homemade alcohol.

Nutt also testified about the scale he helped develop which rated the harmfulness of 20 drugs using 16 criteria. The group of scientists involved found alcohol to be the most harmful drug based on the damage it caused to people other than the drinker. "We came up with a result that was rather unexpected."

Cannabis was the 11th most harmful drug‚ further down the scale than tobacco and benzodiazepines‚ which are common anti-anxiety drugs.

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