Smoking pure marijuana is at least as harmful to lungs as smoking tobacco, a report from the British Lung Foundation concludes. And in some key ways, it may be more dangerous.

For example, the BLF’s review of previous research highlights that just three marijuana joints a day causes the same damage to the lung’s airways as 20 cigarettes, mainly because of the way joints are smoked.

Individually, cannabis and tobacco produce the same constituents and quantities of chemicals known to be toxic to respiratory tissue, other than nicotine, the report says. But when cannabis and tobacco are smoked together, the health effects are worse.

“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,” says Mark Britton, chairman of the BLF. A UK survey conducted earlier in 2002 found that 79 per cent of children believed cannabis to be ‘safe’.


Deep breath

A key finding highlighted by the review of 90 published papers is that the amount of smoke taken into the lungs is two thirds larger if cannabis is being smoked. The smoke is also taken one third deeper into the lungs – and that smoke is held an average of four times longer before being exhaled.

“You inhale deeper and hold your breath with the smoke for longer before exhaling. This results in more poisonous carbon monoxide and tar entering into the lungs,” says Helena Shovelton, BLF’s chief executive.

Other points in the report include:

 Tar from cannabis cigarettes contains up to 50 per cent higher concentrations of carcinogens benzathracenes and benzpyrenes than tobacco smoke

 THC, the primary psychoactive ingredient of cannabis, decreases the function of immune system cells that help protect the lungs from infection

 The average cannabis cigarette smoked in the 1960s contained about 10 milligrams of tetrahydrocanabinol (THC), the primary psychoactive ingredient. Today, it may contain 150 mg.

“This means that the modern cannabis smoker may be exposed to greater doses of THC than in the 1960s or 1970s,” says the report. “This in turn means that studies investigating the long-term effects of smoking cannabis have to be interpreted cautiously.”

Mouth spray

Cannabis is the most widely consumed illegal drug in the UK. In 2000, almost 45 per cent of 16 to 29 year olds in the UK said they had used cannabis at some point.

“We are not making any policy recommendations. The aim of this report is to try to inform the public that if you do choose to smoke cannabis, be aware of the health risks,” says a BLF spokeswoman.

Cannabis-based medicines could be prescribed for medical use in the UK as early as 2003, following the recent success of final-stage trials. But medicinal cannabis is supplied through a mouth spray or in tablet form.

“We have always been keen to find additional ways of administering cannabis as a medicine,” says Nina Booth-Clibborn of the UK’s Medicinal Cannabis Research Foundation. “It did seem that smoking would not be the best way.”

Lyndon Pugh, editor of pro-cannabis magazine CC Newz, is not impressed by the report: “These allegations have been made before countless times. Lot of things are dangerous, like driving.”