Leave it to teenagers to figure this one out.

Edmonton's Public and Catholic school boards are cracking down on e-cigarettes after they discovered five incidents in the past two weeks where students were using the devices to smoke marijuana.

And despite the amount of students getting caught, it's not so easy to detect, say police. Students replace the "juice" in the e-cigarettes with marijuana oil — a process which essentially eliminates the odour of the drug.

The information that we're seeing is that it's prevalent, it's everywhere," Sgt. Kelly Rosnau, with EPS' School Resource Unit, told The Edmonton Sun.

"Kids are jumping on this very quickly."

Staff Sgt. Pierre Blais told the Edmonton Journal the method is "discreet" because it produces no odour and that some students are doing drugs "in a brazen manner."

According to The Edmonton Sun, marijuana oil can contain a THC level as high as 90 per cent — compared to the 10 to 20 per cent THC levels typically found in rolled joints.

There is also concern about the process under which marijuana oil is made.

Rosnau told CBC News marijuana oil production uses significant amount of highly flammable chemicals that could lead to explosion.

Both the Edmonton Catholic School District and Edmonton Public Schools will ban on e-cigarettes for both students and staff on school property.

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  • Cannabis baked goods

    "We stink up our kitchen, so you don't have to stink up yours," says A.J. Ashkar, aka A.J. Hashman, owner of At Home Baked. Instead of selling packaged cookies or brownies, At Home Baked sells brownie, blondie and other mixes that people can bake in their own homes. Normally, says Ashkar, the activation of THC in the oven will create a smell that permeates the whole house. However, because his mix contains a packet of cooking oil infused with activated THC, Ashkar claims "the only thing you smell baking is brownies." These days in Colorado, though, baking anything with cannabis has become easier and more accurate. Most shops sell cannabutter as well as cannabis-infused cooking oil and a portion of either of these can be substituted for regular butter or oil in a recipe. Some quick math will help the chef figure out how much active THC will be in each serving. Ashkar recommends mixing the ingredients very thoroughly before baking, then cutting the finished product into equal parts.

  • Vape pens

    Vaporizer pens have become very popular with medical and recreational users. They are discrete and create very little smell. Users think they're a good alternative to joints and bongs. The cartridge, filled with hash oil, is sold separately from the pen. To begin, you charge the pen by plugging it into any USB outlet. Once the pen is charged, you can insert the cartridge and "smoke" it like an e-cigarette. As the user inhales, the hash oil is vaporized. Small lights at the bottom of the pen shine white as you inhale. They stay on for about six seconds, then start to flash to indicate that the hit is over. In this controlled way, one cartridge provides about 50 to 60 hits, and the user knows how much THC she is getting with each hit. There's a window in the vape pen so that the user can see the level of the hash oil in the cartridge, so she knows when to replace it.

  • Lotions and rubs

    The advertising claims these cannabis-infused topicals won't make you high but will reduce inflammation, relieve muscle and joint pain, reduce swelling and ease stress. Many people who use them swear by them. But there's still scant scientific literature to back up the claims. Nevertheless, people like attorney Cheryl Smith, executive director of a medical marijuana clinic in Eugene, Ore., and onetime "total skeptic," find themselves convinced. Smith, who a few years ago researched the medical literature and published an article called <a href="http://www.compassioncenter.net/topical-cannabis-preparations" target="_blank">"Topical Cannabis Preparations: Snake Oil or Healing Options?"</a> has become a convert. "It does penetrate to the muscle, I'm convinced," says Smith. Using an infusion of her own that she's had tested in a lab, Smith's own experience has made her an advocate. "All this is anecdotal," she says. "I question some of the products. I just know this one works."

  • Cannabis candy …

    Three years ago, says Incredibles' Eschino, "the edibles and concentrate market ... was about 10 percent of the business. The last study I saw ... it's closer to 40 percent of our business now." According to Brian Ruden, co-founder of the medical and recreational marijuana dispensary Starbuds, recreational edibles are all limited to 100 milligrams of active THC. It's easy to portion the candy and figure out how much THC is in each bite. And they taste, says Ruden, pretty much the way they look—like chocolate, raspberry or strawberry candy. All the more important to keep them away from the kids! Every package, says Eschino, must be child resistant.

  • … Including every candy under the sun

    Recreational cannabis candy comes in every variety imaginable. These are just a few sold by Incredibles in Lakewood and Kine Mine in Idaho Springs, Colo. Unlike marijuana that's smoked, eaten cannabis products take about an hour to produce a full effect. It may be easy for a beginner to eat too much. Genifer Murray, trained in microbiology and CEO of CannLabs in Denver, suggests the beginner start with 5 milligrams of THC in an edible. "You can't die from it," Murray says of overdosing, "but you can feel like you're dying." If you smoke too much, the effect subsides quickly. But if you eat too much, says Murray, the bad feelings can last for hours. She suggests that people who have problems with anxiety or paranoia might want to try edibles that have more CBD (cannabidiol) which is a non-psychotropic cannabinoid that, Murray says, "kind of curves the psychoactivity of THC."

  • Shatter

    While marijuana is about 15 to 18 percent THC, says Ruden, concentrates are about 80 to 90 percent. They are smoked in "dabs," a tiny bit at a time, vaporized in superheated bongs. The bud, or flower, of the marijuana plant is dried and sold to smoke; the trim—the leaves and stems—is made into concentrate. At one time, the concentrate was hash, made with a process involving ice water. That was before butane came into play. Shatter is a concentrate made by stripping THC and other cannabinoids from the plant and pooling them in a concentrated mass. The process involve using hydrocarbons, usually butane, sometimes carbon dioxide. The marijuana is suffused with butane under pressure, the concentrate drips out, and then the residual solvent (that is, the unwanted butane) must be evaporated, or "purged," from the concentrate. When the finished hash concentrate is hard and glassy, it's called shatter. <strong><a href="http://www.cnbc.com/id/101435142/page/6" target="_blank">For more weed edibles, check out CNBC.</a></strong>