Dominic Anderson threw himself in front of cars and attacked police officers with the blade during a psychotic episode brought on by the drug.

Today the 20-year-old warned other teenagers about the dangers of using cannabis.

The sports science undergraduate said: 'The first thing I remember was waking up in hospital bed and seeing nurses and police stood around me.

'I couldn't really remember what had happened. It was all a blur. There were bits I could recall but it was like I had been watching myself do all these things and I couldn't help it.

'I'd only taken cannabis a couple of times before and thought it was just a social thing people did to chill out. But in reality it's completely different and can have horrific consequences.

'People need to be more aware of what can if happen if you take cannabis and it starts with the government reclassifying it – it should not be seen as a soft drug.

'People need to know that cannabis is not cool.'

In 2004, the then home secretary David Blunkett downgraded the drug's classification to class C, the lowest, which meant the penalties for getting caught with it were reduced.

Anderson's father, Clive Anderson, 41, added: 'This has been six months of hell for Dominic and our family.

'It has shown us the truly horrific effects that cannabis can have on people.'

When officers tried to restrain Anderson he lunged at them with the knife. He had to be repeatedly hit with a baton before he was disarmed.

He sustained self-inflicted injuries and needed half a dozen stitches in each wrist.

He also suffered internal bleeding and was in intensive care after the incident which happened at the Bradford Road junction in Portsmouth on November 13, last year.

Police said Anderson's actions showed a shocking similarity to the computer game – Saints Row – which he had been playing just before he slit his wrists.

Drugs intelligence officer Detective Constable Steve Kelly said: 'People don't know the effect a drug can have on them before they take it. This is an extreme example of what can happen.'

At Portsmouth Crown Court Anderson, of Britannia Road North, Southsea, was spared an immediate prison sentence.

Instead Judge Graham White imposed a nine-month prison sentence suspended for two years saying: 'It was your taking of the cannabis that led to this psychotic episode but for this you would have never been involved in this kind of behaviour.'

Anderson, who admitted one count of affray, was also ordered to complete 150 hours community service.