Health warning to pot smokers

Cannabis could kill 30,000 Britons a year, senior doctors have warned.

According to a report published in today's issue of the British Medical Journal, many of Britain's 3.2 million cannabis smokers face a future scarred by physical and mental ill health.

The research, led by Professor John Henry of Imperial College School of Medicine in London, found that cannabis gives off 4,000 chemicals when smoked.

Those chemicals are similar to the ones given off by tobacco and many cause cancer and lung and heart disease.

Although cannabis joints are smoked less frequently than normal cigarettes, people often inhale much deeper and for longer, the research said.

The nicotine equivalent in cannabis - tetrahydrocannabinol - can also increase by more than four times the chances of having a heart attack within an hour of taking it, and the researchers found that the average cannabis sample sold on the UK black market is now 10 times stronger than it was 20 years ago.

There are 120,000 deaths a year among Britain's 13 million smokers, leading the doctors to calculate that 30,000 of the 3.2 million regular cannabis users would succumb to similar diseases every year.

The research also pointed out that regular use of cannabis was associated with a higher risk of mental illnesses, such as schizophrenia and depression.

"At present, there is no battle against cannabis and no clear public health message," wrote the authors. "Even if the number of deaths attributable to cannabis turned out to be a fraction of that figure, smoking cannabis would still be a major public health hazard."