The legalization of marijuana in Canada is just five months away, but there are still questions and misconceptions in many people's minds surrounding cannabis.

Matthew Hill, an associate professor at the University of Calgary's Hotchkiss Brain Institute, is working to debunk the myths.

He was part of a panel discussion on cannabis this week at the U of C and also appeared on The Homestretch to dispel some of the misunderstandings about marijuana.

Below is an abridged version of that conversation.

Myth: Teenagers who smoke a lot of cannabis can develop mental illness, schizophrenia in particular, true or false?

A: Somewhere in the middle but definitely closer to false depending on exactly how you look at it. There is definitely some relationship that's out there between cannabis use and adolescence and the development of schizophrenia, which is the main mental illness that has been linked to cannabis use in teenagers.

But it's very difficult to actually figure out if this is causative, in the sense that someone who had never developed schizophrenia smokes pot and suddenly develops schizophrenia. Or, what I think the data more likely would suggest, is that if someone is vulnerable to develop schizophrenia, cannabis can act as one of the triggers that will bring an episode on.

It might bring the disease on earlier and it might make the course of the disease last longer and be worse in the long run, but that's a fundamentally different thing than saying using the drug can cause the disease out of nowhere.

Myth: Cannabis alters brain structure.

A: That one I would say, right now from the current studies, that would be false. There's certainly no compelling data to show that cannabis use, either as adolescents or as adults, really causes structural changes in the brain that are entirely attributable to cannabis by itself.

A lot of the work that's been done — one study shows one effect, one shows another effect — and there was a really good paper that came out recently that aggregated a whole bunch of the data from the studies and it basically showed they often cancel each other out.

And if you look at the whole data set together, there really isn't a lot of effects on the brain. And many of the studies where they see effects, those effects actually could likely be attributed for by other variables like alcohol use, cigarette smoking, life stress and sensation seeking, risk taking behaviours that may have existed beforehand.

Myth: After legalization, more teenagers will smoke pot.

A: That's definitely false. From all the data we've seen out of the United States, there's certainly nothing to support that as of now. In fact, teenagers are certainly the one age group that seemed to show no change at all in response to changes in legal status of cannabis for use patterns.

There's some data that even suggests that younger teenagers, looking at Grade 8 or Grade 10, had a slight decline in use post legalization. And looking at Grade 12, there was no difference, pre and post [legalization]. That being said, you do see a bit of an uptick in use patterns from older age groups, and interestingly, the age group that seems to show the biggest magnitude of change in terms of starting to use cannabis post legalization is actually 55-plus.

Myth: Marijuana is addictive.

A: This is a difficult one to answer just because the word addiction is very contentious in the field. There certainly is a subset of people who use cannabis heavily, who develop use problems. Some people would call it dependency, some would call it addiction. I'm not an addiction researcher, so I'm not comfortable using exact terms. But there does appear to be a cluster of people who develop problematic use where they're using too much. It's influencing the way they conduct their life.

Estimates are putting it between eight and 10 per cent of people who use might develop problematic use patterns. This seems to be more common if you're a male, it seems to be a lot more common if you're consuming cannabis with high THC and it does seem to be more common if you start using younger.

Myth: Marijuana is a gateway drug.

A: I'd say the whole idea of cannabis being a gateway drug is a debunked thing at this point in the sense that people who use cannabis suddenly develop a propensity to use more drugs. I would say most likely what you see is cannabis is more typically an entry level drug.

Most people who start experimenting with substances don't just start with crystal meth or cocaine, for example. They're going to start with a more kind of socially acceptable substance like alcohol or cannabis.

People go to a liquor store to get alcohol because it's a regulated substance. But cannabis right now, because it's not legal, people turn to illicit means to access it typically, and by doing so, that may actually put them in the realm of access to other drugs they normally wouldn't have access to, or try.

But that's different, I think, than the idea that as a gateway drug, cannabis would trigger people to start wanting to try new drugs. I don't think there's any evidence to support that.

Myth: Cannabis impairment isn't as dangerous as drinking and driving.

A: Based on the evidence we've seen, it's still problematic and dangerous to drive intoxicated on cannabis. Most of the studies that have been done on this, when they do simulator studies with people who've gotten intoxicated on cannabis, they do find they do show impairments. But the impairments are less in magnitude than what you see with alcohol and they are different in nature, it seems.

It seems like a lot of people, when they are under the influence of cannabis, are actually aware they are intoxicated and impaired in some capacity. So there's compensation behaviours, they tend to drive slower, they space themselves out more because they feel uncomfortable. Whereas with alcohol, people often don't seem to recognize this. They don't realize they're driving fast and their reaction time is impaired in some capacity.

It's not to say [marijuana] is not dangerous. It's just to say it's probably less dangerous than what you would see with alcohol, which is probably why you haven't seen this massive uptick in fatal motor vehicle [crashes] in states that went legal.


With files from The Homestretch