Today's class C cannabis more dangerous than yesterday's class B

The downgrading of cannabis from a class B to class C drug, scheduled for the end of January, has blown the debate on the safe use of the drug wide open.  

Under the new classification, users are unlikely to be arrested for mere possession. But at the same time as trials are suggesting that cannabis appears to be beneficial in diseases such as multiple sclerosis, there is increasing concern over casual use. Even Rosie Boycott, who as editor of the Independent on Sunday campaigned for the legalisation of cannabis concedes that modern dope is very different from that smoked in the 60s and 70s. 'It's got more dangerous with THC.'

THC or tetrahydrocannabinol is the major active chemical compound in much of today's cannabis. THC causes psychosis. It distorts perception, flattens emotions and can lead to hallucinations, voices in the head and depression. This is on top of the damage cannabis causes to the lungs — cannabis contains many more cancer causing ingredients even than tobacco.

Last week's You and Yours programme on BBC Radio featured a stream of people who thought cannabis-induced psychosis had destroyed their children or their siblings lives.

Professor Robin Murray from the Institute of Psychiatry compares cannabis-induced psychosis to alcoholism — a small minority of cannabis users may become psychotic just as a small minority of drinkers will become alcoholics. He said that the problem was exacerbated today because users were starting younger and smoking more - both of which increase the risk. 'Until the last couple of years, we didn't have definitive studies. Now we do,' he said. 'It's a time-bomb that's already gone off in London. We have twice as many people who are psychotic than in the 1960s.'

Rosie Boycott said the rise of THC was a good reason for the government to start looking at the drug seriously. 'We don't want the drug to be adulterated in this way,' she said.

The evidence is that the debate on cannabis is shifting from 'should it be legal?' to 'how safe is it?' which has got to be a good thing.

To listen to the You and Yours clips, click here. (This link will be removed by the BBC in due course.)