Cannabis is now legal in many US states – but can the smell get you in trouble?

As states around the country continue to legalize recreational and/or medical cannabis use, more are beginning to treat cannabis like alcohol when it comes to policing intoxicated driving.

A recent unanimous decision by the Illinois supreme court found that the smell of burnt cannabis alone does not give police license to conduct a warrantless vehicle search, making it the sixth state supreme court to make such a ruling. In contrast, Wisconsin’s supreme court ruled the opposite just last year . They found that cannabis odor in a vehicle is probable cause to justify a search (unlike in Illinois, adult recreational cannabis is still illegal in Wisconsin).

Police have had the right to search vehicles without a warrant since the 1920s, the era of alcohol prohibition . The supreme court in 1925 found that police could search vehicles if they had probable cause to believe drivers were transporting contraband alcohol. Even after prohibition ended, police still retained this right, which is why they can search vehicles when they suspect drivers are drunk or high.

Paula Savchenko, an attorney and founding partner of the Cannacore group, which helps cannabis businesses get licensed, says that in states where cannabis is legal, courts are starting to treat it more like alcohol – recognizing that the product itself is legal, but driving while impaired with it is a crime.

“When officers are investigating a driver for a DUI, the smell of alcohol is a relevant factor, however, they tend to conduct further investigations to corroborate their theory,” she said.

The Illinois supreme court decision does allow cannabis smell to be a factor in determining probable cause, but not the only factor.

Will Garriot, a professor and chair of the law, politics and society program at Drake University, says: “Cannabis odor has been an important enforcement tool for police for a long time.”

Before states began to legalize adult recreational cannabis, possessing cannabis alone was a crime so smell could justify a search.

“Now, the bar has been set a little bit higher,” he says.

Police officers must learn to recognize other signs that someone is high on cannabis, because, unlike with alcohol, there’s not yet an agreed-upon, reliable test like a breathalyzer for cannabis.

The Illinois supreme court decision referred to the smell of “burnt cannabis” specifically because Illinois also has a law requiring drivers to transport cannabis in odor-proof containers.

A variety of local laws around the country require cannabis consumers to keep their smells to themselves. Last year, for example, Minnesota passed a law banning cannabis consumption in multi-family housing.

Christopher Strunk, an attorney who specializes in cannabis and environmental regulation, says that these laws can be “problematic”.

“In my opinion, there’s not necessarily a rational basis for those laws,” says Strunk. “Unless you really get down to smell it, it’s not going to emanate this major odor.”

He added that these laws do “give police, or municipalities or jurisdictions that don’t like cannabis, an excuse to enforce it”.

Additionally, laws like these also tend to target more vulnerable populations, such as unhoused people and people of color.

Other odor-creating industries, such as wineries, breweries and landfill companies, face similar pressures, says Savchenko.

“Vermont has required air pollution control permits for hard cider facilities due to its large boilers, and for whiskey distilleries due to aging in wooden barrels,” she explained.

Related: Supreme court’s Chevron decision adds ambiguity to cannabis law: ‘It’s a mess’

While laws targeting individual consumers might be selectively enforced, environmental laws such as the Clean Air Act apply to all industries that might produce a stench, including the cannabis industry. Some states, Savchenko says, require cannabis manufacturing businesses to submit an odor control smell plan before they’ll provide them licenses.

Still, cannabis manufacturing odors can be a huge source of community tension. Strunk pointed to an ongoing battle in Santa Barbara county, which produces 40% of California’s cannabis.

Residents of the beachside town Carpinteria filed a class-action lawsuit claiming that a “sewer-like” smell from several cannabis plants was causing their property values to decline. Carpinteria residents are now fighting to require cannabis facilities to obtain carbon scrubbers, which cost more than $20,000 a piece, to get rid of odors.

“Any activity or business that produces an unpleasant odor may violate the law and trigger enforcement, though not every complaint leads to action,” says Garriot. “Lots of people end up living with odors they don’t like , or they tolerate them because they are produced by, say, a business that is the biggest employer in town.”