Pubdate: Fri, 14 Apr 2017
Source: Globe and Mail (Canada)
Copyright: 2017 The Globe and Mail Company
Author: Kelly Grant
Page: A9
Referenced: Cannabis Act:


As Justin Trudeau's Liberal government tables its long-awaited
marijuana legislation, Canada's doctors have a message about pot: Just
because it will eventually be legal doesn't mean it's safe.

The Canadian Medical Association, the Canadian Psychiatric
Association, the Canadian Paediatric Society and other organizations
representing front-line health-care providers have been busy
broadcasting their concerns about the ill effects of cannabis,
especially for chronic smokers under the age of 25.

"We're saying: 'Please keep the public-health focus front of mind as
this legislation is unrolled,' " said Gail Beck, the clinical director
of youth psychiatry at the Royal, a psychiatric hospital in Ottawa.
"Lots of people think this is harmless."

The medical profession in this country has long had misgivings about
medicinal marijuana-namely, that there is not enough solid evidence
of pot's efficacy in treating chronic pain and other ailments to
warrant a doctor's endorsement. But with the advent of legal
recreational marijuana, doctors have a different set of worries.


One top-of-mind concern: The potential for addiction to marijuana,
especially among teens and young adults. "We know that one in seven
teenagers who start using cannabis will develop cannabis-use disorder,
which is significant," said Christina Grant, a professor of pediatrics
at McMaster University in Hamilton.

Cannabis use crosses over into disorder territory when it begins to
cause dysfunction in users' day-to-day lives, derailing their
commitment to school or work and sowing conflict in their families,
said Dr. Grant, the lead author of the Canadian Paediatric Society's
position statement on marijuana, released last fall.

Mental illness

Cannabis has also been linked to certain mental illnesses. The drug's
relationship to depression and anxiety is still up in the air; the
science has not established a causal relationship between the two. In
other words, it's not clear if people smoke pot because they are
depressed and anxious or are depressed and anxious because they smoke

There is stronger evidence that heavy use of cannabis can lead to
psychosis, especially among people who have a family history of mental
illness, Dr. Beck said. However, the vast majority of the research
involved people who use cannabis daily. The scientific literature is
virtually silent on the mental-health effects of smoking pot now and

"We don't know the lower limit that's safe," Dr. Grant cautioned.
"There's no evidence to say, yeah, use it once, use it twice and
nothing will happen."

The developing brain

There is good evidence that teens who smoke pot frequently suffer
long-lasting damage to their still immature brains, including problems
with memory, attention and executive functioning. "For teenagers who
use cannabis regularly, there's actually structural changes [visible]
on MRI," Dr. Grant said. "They show that certain areas of the brain
are smaller, there's thinning of a part of the brain called the
cortex, which is very important in terms of thinking and planning and

The adult brain appears capable of recovering from chronic pot use in
a few weeks. "That's not what happens in young people," Dr. Beck said.
Citing concerns about the adolescent brain, the Canadian Medical
Association last year urged the federal government to ban the sale of
marijuana to people under the age of 21 and to restrict the amount and
potency of the drug available to those younger than 25.

Driving while high

Most of the health concerns associated with cannabis apply to heavy
users. But occasional tokers can wreak havoc if they get behind the
wheel while high. "Cannabis impairs your ability to safely drive a
vehicle," said Amy Porath, the director of research and policy for the
Canadian Centre on Substance Abuse (CCSA). "It impairs your reaction
time. It impairs your ability to multitask and pay attention." Police
across the country are currently piloting a roadside saliva test to
see if it adequately detects cannabis-impaired drivers.

Your lungs on pot

"Whether it's tobacco or cannabis," Dr. Porath said, "there are
concerns with smoking anything." Smoking pot can cause coughing,
wheezing, sore throat and tightness in the chest. It can also
aggravate asthma. Although marijuana smoke contains many of the same
cancer-causing chemicals as cigarette smoke, the evidence that
pot-smoking causes lung cancer is mixed, according to a review of the
evidence by the CCSA.

The same is true of cannabis smoke and chronic obstructive pulmonary
disease, or COPD, an umbrella term that includes chronic bronchitis
and emphysema. Recent studies have suggested "no causal relationship"
to COPD in cases where patients smoked low-to-moderate amounts of pot,
the CCSA report said, but more research is needed among heavy smokers
of the drug.
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