The person to ask is Donald Tashkin, a lung expert at the University
of California at Los Angeles. For the past 15 years, Tashkin's team
has been keeping a close eye on the respiratory systems of more than
130 regular marijuana smokers, comparing them with groups of people
who smoke either just tobacco, tobacco and marijuana, or nothing at
all. It's the biggest study of its kind in the world. And the results
so far suggest that in some respects, yes, marijuana is more dangerous
than cigarettes. But in one important respect, joints may actually be
better for you -- especially if you're an athlete.
First, the bad news. While the cigarette smokers in the study were ploughing
through 20 or more a day, the marijuana smokers seldom consumed more
than three or four joints. Despite this, the marijuana smokers coughed
and wheezed as much as the cigarette smokers. In both groups, about
one in five people complained of coughing up phlegm and suffering bouts
of bronchitis.
And when it came to cellular damage to the lungs, there was also little
to choose between them. Both groups had too many mucus-secreting cells
lining their airways and too few hair cells, and both groups showed
evidence of abnormalities in cell nuclei and changes in genes known
to have an early role in the development of cancers.
The similarity may seem puzzling given that the marijuana smokers were
consuming so much less plant material. But there are good reasons for
it, says Tashkin. The first is that joints yield up to three times the
tar of cigarettes because they are more loosely packed and don't have
filters. The second reason is that marijuana smokers inhale more deeply
and hold their breath longer.
"We
actually quantified this and found that the breath-holding time was
increased about fourfold," says Tashkin. "That resulted in about a 40
per cent greater deposition of tar." Tashkin's final factor -- contested
by some researchers -- is that marijuana smoke is richer in benzopyrene
and other polycyclic aromatics known to trigger cancerous changes in
cells.
So smoking marijuana can cause lung cancer, after all? Well, maybe.
Despite the gloomy cell biology, epidemiologists have so far failed
to find a link between marijuana and serious lung diseases. That might
be because there isn't one. Or it might be because "the marijuana epidemic"
(as Tashkin calls it) is still young and the people who started smoking
in the 1960s haven't reached an age when cancers become common.
Meanwhile, some researchers are worried about another aspect of marijuana
smoke -- its ability to interfere with immune cells that help to fight
off lung infections. Tashkin's team has just discovered that immune
cells isolated from the lungs of marijuana users are unusually bad at
killing bacteria, 35 per cent worse, in fact, than similar cells taken
from cigarette smokers. The marijuana-exposed cells were also below
par at producing molecules needed to mount inflammatory responses. In
normal marijuana smokers, the effects may be too slight to make much
difference. Tashkin fears, however, that the same might not be true
in people with AIDS, many of whom use cannabis to stimulate their appetites.
Footballer's fancy
There's some good news, though, for dope-smoking cricketers and footballers:
marijuana smoke won't lead to blocked airways or emphysema. Despite
all the cellular changes noted by Tashkin's team, the researchers found
that even heavy smoking of marijuana had no impact on any physical measure
of lung function. In fact, among their subjects, smoking three joints
per day caused no greater rate of decline in lung capacity and the ability
to breathe than smoking no marijuana per day.
And the reason for this silver lining? It could well be back to those
sluggish immune cells, speculates Tashkin: "If cannabis impairs the
ability of immune cells to produce inflammatory cytokines, you might
be spared mucosal damage in peripheral airways."
