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.
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."
