Following last year’s decision to tighten up the law on cannabis, the Government has launched a campaign to warn teenagers of the dangers of using the drug.

The Department of Health has launched what it terms as a “hard-hitting” media campaign warning young people that the drug can “mess with your mind”.

The drug was moved down from the class B drug category to class C in 2004 by then Home Secretary David Blunkett.

The move was disastrous, with crime and mental health problems associated with cannabis use soaring in subsequent years.

Cannabis was restored to class B last year, but according to the Department of Health: “The false perception still exists amongst some young people that cannabis is a safe drug despite the fact that it can produce both immediate and longer-term harms to mental and physical health.”

The department says cannabis is now used by almost 18 per cent of 16 to 24-year-olds.

There has been criticism that while the drug has been returned to class B, confusion has been created by the decision to adopt a ‘three strikes and you’re out’ approach to users.

Those caught with the drug will only face arrest in the third instance – first they will receive a warning, and then an on-the-spot fine.

Last month it emerged that teenagers in the North East of England were being given tips on how to use the drug in a publicly-funded booklet called Know Cannabis.

The booklet told readers that cannabis can make music “sound better” and explained how to roll a joint. The fact that cannabis is illegal was not pointed out until over halfway through the booklet.

But launching the new campaign, Public Health Minister Dawn Primarolo said “Cannabis is a destructive drug. What can start as a few giggles and being part of the crowd can have serious and long-term health problems.”

National Director for Mental Health Services Louis Appleby added: “Cannabis is a harmful drug that can damage your mental health. We have known for years that it can be part of a pattern of relapse and risk in people with severe illnesses such as schizophrenia and bipolar disorder.

“Now the evidence is pointing to cannabis as the cause of psychosis in some people, particularly people who are heavy users.”