Potent Pot: How marijuana got so strong and what it means for legalization

Some experts say that marijuana is becoming more potent because of consumer demand, and that recreational users should beware of its effects, especially young people.

The federal government is running a $5-million ad campaign aimed highlighting the risks that marijuana can pose to young users, claiming that marijuana is on average 300 to 400 percent stronger than it was 30 years ago. It coincides with a growing body of research about the impact that marijuana could have on brain development, and a new study that shows pot smoking can alter the shape of the brain. Researchers at the University of Texas took brain scans of cannabis users aged 20 to 36 and they found that over six to eight years of continual use, their grey matter shrunk.

But the researchers also found that the brains of young marijuana users were able to compensate for the damage, by increasing their neuron connectivity. But after about five years of smoking pot, that boost in connectivity diminished.

This research backs up the message of Health Canada's anti-drug campaign."Health Canada is reacting to scientific studies that have explored the consequences of medical marijuana use on young brains," says Lesley Campbell, plant evolutionary biologist at Ryerson University, who studies marijuana growing conditions.

"It seems as if there is a long term consequence to habitual use by teenagers. When we talk about teenagers we forget that brains develop in humans up until at least 24-years-old so that developmental stage can be quite broad and should include more young people than just teenagers," she adds.

According to John Anderson, a former corrections officer and pro-legalization advocate, Health Canada's numbers may be right but the way they are expressed could be misleading. "On a percentage basis that does sound a bit outlandish," he says. "If you look at the difference between one and four percent that's 300 percent so I suppose they have an argument there. But I think that's beside the point. The strains that we are seeing and the concentrations that we are seeing I think are a direct result of prohibition."

When approached by CBC Radio's Day 6 for comment, Health Canada points to two studies to back up its claims about marijuana's increased potency. One was published in the 2014 in the New England Journal of Medicine and the other was published in 2012 in Drug Testing and Analysis Both are peer-reviewed, scientific journals.

A Health Canada spokesperson told Day 6 that based on those studies, the THC content in marijuana has increased from an average of about 3 percent in the 1980s to an average of 12 percent in 2012.

THC stands for tetrahydrocannabinol, the primary psychoactive compound in cannabis. Lesley Campbell says back in the 1970s, pot available in Canada would have likely been grown in basement conditions under normal lights or outside in a far off country like Columbia.

Now, growers are engineering strains of pot that are far more potent which are grown under optimal lighting conditions. Campbell says some growers produce pot that has up to 24% THC levels. "People have done a lot of work on hydroponics and artificial lighting systems. People have changed where they purchase their material from, whether it is something that is locally bred and therefore optimized for growing conditions in Canada versus internationally bred which might be less domesticated. And they also choose very specific harvesting procedures so they pick these unpollinated buds rather than the leaves and the stems."

Potency and the push for legalization

John Anderson says prohibition is the primary factor that has driven growers to produce more and more potent strains of pot.

"I think that the trend that we are seeing is something that most economists would recognize: the ability to package a product with a greater concentration of what the consumer demands. And it's driving producers of marijuana to develop strains that are higher in tetrahydrocannabinol," he said.

Anderson says prohibition is driving underground pot producers to increase their profits by reducing the size of the product they are transporting, in other words, by concentrating the amount of THC in their plants.

And he says it all comes down to demand. "At the consumer end there may be a preference in ingesting smaller amounts of marijuana because it means you don't have to go through the somewhat noxious experience of smoking marijuana in the first place. It's hard on the lungs and if you can get a high from ingesting a much smaller amount then it's more attractive." As pot grows in strength, Anderson says so should the push to legalize and regulate it.

"If there is danger in the potency that we are talking about then the solution would be to regulate the production and distribution and marketing of cannabis much in the same way we do alcohol. And if you look at the success that Health Canada has in convincing young people not to begin smoking it's quite remarkable."

When it comes to medical marijuana, Lesley Campbell says high THC levels aren't always best. She says pot that is lower in THC but high in property called cannabidiol can also be medically beneficial. "Cannabidiol is great at relaxing or de-stressing people. Where you wouldn't want a high amount of THC is in places where people already have hallucinations so for instance Alzheimers patients," she said.

Health Canada's cannabis conundrum

A Supreme Court ruling in 2000 gave Canadian patients access to medical marijuana. In spite of the fact that it does not officially condone it, Health Canada is responsible for authorizing its medical use. Critics say Health Canada's campaign to discourage young people from taking up pot has been highly politicized. In August, the main groups representing Canada's doctors refused to participate the recent ad campaign, calling it "a political football on Canada's marijuana policy."

But the groups said they will continue to enhance public education awareness of the health risks of drug and alcohol consumption by Canada's youth. One thing most experts tend to agree on is that smoking marijuana while the brain is still developing can have detrimental effects.

"My preference based on what I've read in the literature is to discourage youth from using cannabis probably until about age 24 or 25," says Anderson. "It's incredibly important to avoid consuming this material before the brain is fully developed," says Campbell. "It can hamper cognitive skills in teenagers which is one of the places where lots of people are very experimental. But we also see short term impairment in terms of motor skills and thought processing," she adds.

In the U.S., where weed is legal in some states, The Department of Justice notes "preventing distribution to minors" as one of eight guideli​nes states should follow in order to avoid federal intervention.

Could legalizing marijuana bring down the demand for potent pot?

Right now, recreational marijuana use is legal in Washington and Colorado, though it is still classified as an illegal narcotic under U.S. federal law. So if Anderson's argument holds true — that prohibition is driving producers to increase the potency of their pot — could legalizing pot do the opposite?

Some recreational dispensaries in Colorado offer recreational pot with THC levels as high as 19 percent. Anderson says, again, it's all about economics. "These are fairly new developments in history and as more states legalize it could be that there is a demand for lower potency marijuana for all kinds of reasons. I've talked to several people who use cannabis medically and they'll tell you that there are strains that really don't make you high. They give you a physical experience but you can continue doing whatever you're doing, reading a book, or engaged in work on a computer without any kind of interference in your thought process," says Anderson.