The prohibition on dagga is the "gateway to harder drug use‚ not the use of cannabis itself"‚ Imperial College Professor David Nutt told the Pretoria High Court.

Nutt‚ a psychiatrist and neuropharmacologist is testifying in the trial to have the current ban on dagga use ruled unconstitutional.

Johannesburg residents Jules Stobbs and Myrtle Clarke are asking the Pretoria High Court to deem the laws banning the adult use and sale of dagga unconstitutional and thus instruct parliament to make new laws.

One of the biggest reasons that governments and drug-affected communities oppose the legalisation of dagga is that it is seen as the gateway to using more dangerous drugs.

"The gateway theory is a theory that has very‚ very little in the way of empirical evidence‚" Nutt said.

"Most people who use cannabis do not go onto harder drugs. Most people who use harder drugs [first] use things other than [in addition to] cannabis."