POT LESS OF A CANCER RISK THAN TOBACCO, STUDY SUGGESTS

Nicotine in Cigarettes Appears to Boost Carcinogenic Properties,
Researchers Find

Marijuana smokers are less likely to contract cancer than cigarette
smokers, new research suggests.

While cannabis and tobacco smoke are chemically similar, the key
difference is that cigarettes contain nicotine, which appears to
bolster the cancer-causing properties of tobacco, while cannabis
contains tetrahydrocannabinol (THC, the active ingredient in pot),
which may actually reduce the carcinogenic properties of some chemicals.

"Current knowledge does not suggest that cannabis smoke will have a
carcinogenic potential comparable to that resulting from exposure to
tobacco smoke," said Robert Melamede, chairman of the department of
biology at the University of Colorado at Colorado Springs.

The new study, published in today's edition of the medical journal
Harm Reduction, is a review and analysis of research that has already
been published.

The research has important political implications in the ongoing
debate about medical marijuana.

One of the principal reasons public-health officials and medical
experts oppose the use of marijuana as a prescription drug is the
belief that the risks outweigh the benefits, and the fear that
endorsing medical marijuana undermines anti-smoking campaigns.

Marijuana contains about four times the level of tar found in
cigarettes, and is believed to place smokers at risk of lung cancer
and other cancers related to smoking.

But Dr. Melamede said there is no solid evidence that cannabis smoking
increases the risk of lung cancer or other cancers related to tobacco
smoking such as breast, colon and rectal cancer.

He said there is evidence from studies done on laboratory rats that
the THC in cannabis smoke "exerts a protective effect" against
potential carcinogens and evidence that nicotine found in cigarettes
activates the growth of tumours.

"While both tobacco and cannabis smoke have similar properties
chemically, their pharmacological activities differ greatly," Dr.
Melamede said.

But Roberta Ferrence, director of the Ontario Tobacco Research Unit
and professor of public health at the University of Toronto, expressed
grave doubts about the research, likening it to splitting hairs.

"It may be that cannabis is slightly less carcinogenic but tobacco
smoke is extremely carcinogenic so that doesn't tell us very much,"
she said.

Dr. Ferrence said that most carcinogens are a byproduct of combustion,
so "anything you burn and inhale is going to be carcinogenic --
including tobacco and cannabis. There is no way, based on this
research, that you can say that smoking cannabis is safe."

She also noted that many people who smoke marijuana mix it with
tobacco, and that makes the chemical distinctions moot. "From a
public-health perspective, smoking is smoking," Dr. Ferrence said.

Tobacco smoke contains more than 4,000 chemical compounds, dozens of
which are known carcinogens.

An estimated 5.1 million Canadians, or 20 per cent of the population
15 and older, report smoking cigarettes regularly, according to the
Tobacco Use Monitoring Survey. More men (22 per cent) smoke than women
(17 per cent).

By contrast, an estimated three million people, or 12.2 per cent of
those 15 or older, reported that they smoked marijuana at least once
in the past year, according to Statistics Canada.

Nearly half (47 per cent) of those who had used cannabis in the
previous year smoked less than once a month, 10 per cent reported
weekly use, and another 10 per cent said they smoked pot daily.

Canada has had a medicinal marijuana program since 2001. Since then,
Health Canada has issued about 750 licences for people to smoke
marijuana for the treatment of chronic pain and other ailments.