"Cannabis does not cause schizophrenia." This is the conclusion of Professor David Nutt, psychiatrist. neurologist and director of the Neuropsychopharmacology Unit at London's Imperial College.
Nutt is testifying in High Court in Pretoria in a civil case brought by Johannesburg residents' Myrtle Clarke and Jules Stobbs. The pair, nicknamed "the Dagga (cannabis) Couple", are asking to have the laws banning dagga repealed and sent to parliament to be reworked.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 harmâ€š 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 policyâ€š 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 thirty-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 increase new cases of the disease. The UK did not see an increase in schizophrenia.
"This shows cannabis cannot cause schizophrenia. Schizophrenia is a very rare disease." Nutt admitted that dagga use can lead to temporary psychotic symptoms.
A state witnessâ€š Harvard Medical Professor Bertha Madras who will testify on paper for the governmentâ€š says dagga use leads to an earlier onset of schizophreniaâ€š which usually first appears in a person's twenties. Doctors for Life will also testify 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 cannabisâ€š where as 8,000 people die from alcohol use a year in the UK."