Monday, 11 November, 2002, 01:47 GMT

Smoking pure cannabis is just as harmful to lungs as tobacco, a health charity is warning.

A study by the British Lung Foundation found that just three cannabis joints a day cause the same damage as 20 cigarettes.

And when cannabis and tobacco are smoked together, the effects are dramatically worse.

Evidence shows that tar from cannabis cigarettes contains 50% more cancer causing carcinogens than tobacco.

Dr Mark Britton, chairman of the British Lung Foundation, said: "These statistics will come as a surprise to many people, especially those who choose to smoke cannabis rather than tobacco in the belief it is safer for them.

Dr Britton emphasised that the British Lung Foundation report - called A Smoking Gun? - was "not about the moral rights and wrongs of cannabis".

But, he said, they simply wanted to make sure people were completely clear about the respiratory health risks involved.

Misconception

Surveys carried out earlier this year showed that 79% of children believed that cannabis was 'safe'.

Only 2% understood correctly that there are health risks associated with smoking the drug.

The British Lung Foundation report also shows that the health dangers of cannabis have substantially increased since the 1960s.

This is due to increased amounts of THC - or delta-9 tetrahydrocannabinol, the major active chemical compound - in the cannabis consumed today.

Pleasure receptors

In the brain, THC connects to specific sites called cannabinoid receptors on nerve cells and thereby influences the activity of those cells.

Many cannabinoid receptors are found in the parts of the brain that influence pleasure, memory, thought, concentration, sensory and time perception, and coordinated movement.

BBCi Science - Hot Topics Click here for more about cannabis

Dame Helena Shovelton, chief executive of the British Lung Foundation, said: "Puff and inhalation volume with cannabis is up to four times higher than with tobacco - in other words you inhale deeper and hold your breath with the smoke for longer before exhaling.

"This result in more poisonous carbon monoxide and tar entering into the lungs."

The British Lung Foundation is calling for the government to implement a public health education on the health risks of cannabis.

The charity will also be pushing for further research into cannabis and the lungs and it's potential link with the development of chronic obstructive pulmonary disease.

-- Anonymous, November 10, 2002