Dr. Laurie Vollen has been encouraging people to use cannabis for decades, recommending thousands of her patients smoke marijuana to treat a wide range of conditions. But the Berkeley medical doctor has a simple message when someone asks her if they should use cannabis vape cartridges: Don’t do it.

Vollen has been critical of cannabis vapes for years, pointing to evidence that the cartridges can expose users to heavy metals and have never been evaluated for long-term health effects. Her concern increased this year after a pesticide scandal swept through the cannabis industry, with many vape cartridges sold in California’s legal stores testing positive for pesticides.

“You’re just getting an increased exposure to another toxin,” Vollen said. “It’s one more piece of evidence that people should not be vaping.”

Cannabis vape cartridges have become an almost irresistible product for cannabis users over the past decade. They can fit in your pocket and need only a handheld electronic battery the size of a pen to work. Just attach the cartridge to a battery, click a button, inhale and voila, you’re on your way to getting high without the smell or annoyance of burning anything.

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Consumers clearly enjoy the products: California sold nearly $100 million worth of vape pens last month, and vapes far outsell pre-rolled joints and edibles, according to cannabis data company Headset. With modern convenience, however, comes a new set of concerns compared with the traditional process of smoking cannabis flower out of glass pipes or rolled into joints.

FILE: A man exhales smoke while legally smoking weed with a vape pen in Washington state.

To start, the cannabis cartridge and battery itself could potentially be toxic to users. A 2021 study that tested legal vape cartridges purchased in Washington state found that heavy metals can leach from vape cartridge components into the vapor that is inhaled from the end of the vaporizer, exposing users directly to potentially toxic heavy metals.

There are also concerns about the cannabis oil inside vaping cartridges. Cannabis oil is extracted from cannabis flower to produce an oily substance that can be over 90% percent THC by weight, far higher than the average 20% THC potency found in dried cannabis flower.

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These extractions don’t only concentrate THC. They can also increase how much contamination ends up in the final cannabis oil, because the process required to turn flower into oil removes plant matter without necessarily removing contaminants. That means cannabis flower that has a relatively low amount of pesticide contamination can become cannabis oil with concerning levels of contamination, with those pesticides becoming a larger portion of the overall product.

California’s Department of Cannabis Control (DCC), the state agency in charge of regulating California’s legal weed industry, told SFGATE that it considers vape cartridges to be “high-risk products” for pesticide contamination. California’s own recall history appears to demonstrate the risks associated with cannabis oils: All 11 pesticide recalls issued this........

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