SPOKANE, Wash. — Just like with alcohol, there is a legal limit for driving under the influence of marijuana.

That legal limit is 5 nanograms or less. However, there is no standard of reference that compares ratio of marijuana usage to levels of impairment.

Washington State Patrol trooper Jeff Sevigney said there is no standard of reference because marijuana affects people differently, varying from person to person.

“One person’s 2 nanograms could be another person’s 180 nanograms and there are a lot of factors that go into that," Trooper Sevigney said.

Factors like how often someone uses marijuana. Just like with alcohol and prescription drugs, if someone uses them frequently, they can develop a tolerance.

WSP Troopers said higher amounts of these substances in your system can correlate with higher impairment.

“There's a whole bunch of factors that go into arresting someone for being impaired and I have no idea how many nanograms of whatever you have in your body,” Trooper Sevigney said.

Troopers will not know how much marijuana is in your system until after a blood draw, which can take weeks to test. Field sobriety tests are used to determine whether or not troopers get a warrant to draw blood.

"We see that a lot with drivers who area heavily impaired by alcohol and they may walk and talk just like you and me, but when you do those impairment tests, that’s when you can see the level of impairment,” Trooper Sevigney said.

Troopers said it is illegal to drive impaired, no matter what tests show. Trooper Sevigney said he has arrested people for impairment who are found to be under the legal level.

“So if you feel you’re impaired, don’t get behind the wheel,” Trooper Sevigney said. “It’s not worth it.”