Calgary police have launched their holiday checkstop campaign, but it’s not just alcohol they're detecting, officers say this year there’s a growing crackdown on drugs.

"We're trying to educate younger people and adults that you know, as well, don't take drugs and drive," said Cst. Len Stefaniuk, a drug recognition evaluator.

Police say marijuana in particular has been showing up at checkstops in recent years.

Up until 2008, officers would often handout an automatic 24-hour suspension if they thought someone was driving while high.

After 2008, a new bill called ‘C2’ was introduced that allowed officers to further investigate those suspicions. The bill included a new drug recognition program and specially trained officers.

"Perceptions of distance and time is actually affected and depending on how much they have consumed, just like alcohol, dependent on the level of impairment," Stefaniuk said.

When officers suspect a driver is under the influence of marijuana or other drugs a standard road side test is performed. If the driver passes they are free to go, and if they fail Stefaniuk says they will be arrested.

"Just like with an impaired driving a demand is read and then they're taken to an office and then the evaluation is completed. At the end of that evaluation if it's determined there is a drug or impaired by a drug we demand they provide urine to confirm what drug and drug category they may be impaired by."

Wayne Jeffrey, a toxicology consultant and former head of the Canadian Society for Forensic Science Drug and Driving Committee, says the public needs to be educated more on the impact drugs have while driving.

"With the decriminalization of marijuana in many states in the United States — Washington and Oregon — people may feel ... marijuana isn't an impaired drug.  Well it is an impairing drug especially when combined with a little bit of alcohol," Jeffrey said.

Some defence lawyers say once these type of cases get to the courts, the question usually will be about how police justified the arrest.

"What indicators are they looking for, what level of training do they have in order to furnish themselves with an objective basis to arrest," said defence lawyer David Chow.