Several states, including New York and Minnesota, don’t allow medical marijuana users to smoke the drug. But some of these qualified users have now found a way around this issue by turning to vaping devices to consume their medicine.

Many vape shops across the country are reporting a wave of new customers that are older nonsmokers suffering from serious illness. These patients are often referred to vape shops by medical marijuana groups who believe the vaping devices pose lower risks than smoking pot. There’s also a level of increased privacy because the vapor released by the heating device is nearly odorless.

JoAnne Leppanen, executive director of the Rhode Island Patient Advocacy Coalition, said that medical marijuana patients prefer vape shops because they “do not want to be associated with recreational use. [They don’t] want their cars to be seen in a dispensary parking lot.”

This is part of the reason why vape shops, many of which are mom-and-pop operations, have exploded in popularity in recent years. The number of U.S. vape shops has jumped to 8,500 since 2008, while the sale of e-cigarettes and related products has soared to $3.5 billion this year and is expected to reach $13.4 billion in 2020. Wells Fargo Securities analyst Bonnie Herzog has even predicted that e-cigarette and vaporizer use will surpass traditional cigarette use in the U.S. over the next 10 years.

But not all health experts are on board with medical marijuana users consuming the drugs through vaporizing. Bob Blake, a San Diego-based physician, said there are unknown health risks with certain types of vape pens. However, he did acknowledge that “people want discretion. With vaporizers, in a large room, a person can be medicating without offending the other person in the room.”

Medical marijuana is currently legal in 23 states and the District of Columbia, while an additional 15 states allow patients with severe seizure disorders to use several strains of cannabis for medical reasons.