After Matt Osmun was injured on the job, he and his wife opened their own business. Most costumers at Grassy Plain Vape & Smoke are there to buy e-cigarettes to help them quit smoking tobacco, but both Matt and his wife Jen are finding a growing number of their customers are medical cannabis patients.

Since 2008, the number of U.S. vape shops has grown to about 8,500, and the sale of electronic cigarettes and supplies climbed to $3.5 billion, according to Wells Fargo Securities analyst Bonnie Herzog. She expects U.S. use of e-cigarettes and vaporizers to overtake traditional cigarettes within a decade.

Cannabis represents an additional lucrative market. IBISWorld, a market research firm, projects sales of cannabis for medical use to increase to $13.4 billion in 2020 from $3.6 billion in 2015, largely due to demand from an aging population with conditions such as arthritis, Alzheimer’s disease and glaucoma.

At a lot of these vape shops, customers are typically older nonsmokers suffering from serious illness. Patients and medical cannabis groups say they prefer the vaping device for cannabis rather than smoking because they believe there are lower risks. Some states, including New York and Minnesota, prohibit patients from smoking cannabis.

Vaping devices, which can be as small as a ballpoint pen, also provide medical cannabis users with more privacy, since the vapor released is nearly odourless.

“Vaporized cannabis is a really significant trend in both medical and adult use,” said Christie Lunsford, a Colorado-based consultant who focuses on issues involving cannabis. “It’s consistent, it’s almost instantaneous, and it’s appropriate for a wide variety of consumers.