Many are concerned about cannabis's negative impact on young people's mental health.

One mother attributes her son's suicide to cannabis -- 18-year-old Matthew hung himself after taking LSD at a party.

"Without a doubt it was the cannabis that started it," said Collette White, 51, of St Mellons, Cardiff.

"It is phenomenally destructive."

White feels that drugs are far more available than when she was young.

"When I was young I knew it was there but we didn't go looking for it," she said.

"Now it is handed to them on a plate -- in schools and in their social circle."

"It's not only the drug but the people who they get involved with."

"You become pressurised into things without even knowing it."

"Some youngsters think they are indestructible but they are not."

"In 18 months Matthew turned from someone who was a really active individual into someone who didn't really want to do anything."

Psychologists in Wales have been studying the effects of cannabis on mental health -- a recent report claims that smoking the drug can increase the risk of psychotic illness by 40%.

"The study that has looked at the risk of psychosis suggests that people who use cannabis regularly, increases the risk two or three fold of developing a psychotic illness later in their lives," said Dr Stanley Zammit, a clinical lecturer in the psychology of medicine at Cardiff University.

"People do need to be aware of the long-term impacts."

"The more people use it the more wary they should be."

"Sometimes people can suffer from psychotic symptoms immediately after smoking cannabis like mild hallucinations."

"The people who suffer these symptoms are most at risk of developing problems in the future in my opinion."

Dr Zammit acknowledges that it is often hard to determine if cannabis is entirely to blame for mental health issues.

"It's a difficult area to study because you can't decide whether it's the cannabis risk or because of other choices in that person's lifestyle or personality," he said.

He also pointed out that the drug has become more readily available in recent times.

"Cannabis use has increased so much over the last 10 or 20 years," Dr Zammit said.

"It's almost abnormal not to use it these days."

Campaigners for the legalisation of cannabis believe that prohibition is making the problem worse -- they see regulated distribution of the drug as the answer.

"Personally, I'm not concerned about these figures as long as these youngsters know what they are doing," said Don Barnard, of the Legalise Cannabis Alliance.

"What really matters is that if one in every ten 15-year-old is smoking cannabis then the government strategy is failing."

"Obviously, our organisation would like to see cannabis legalised and then maybe these youngsters will find it harder to get hold of it when it is controlled."