As of now, yes you can get a DUI or drugged driving charge for having any detectable amount of marijuana in your system. Keep in mind, this could mean you could be arrested for this days after you have smoked. Generally levels of thc can be observed, but the line of intoxication is iffy and pretty much up to the discretion of the [hopefully not] arresting officer. It is illegal to use any intoxicating substance and drive a car in the state of Illinois.
Yes, you can get a DUI if you are caught driving under the influence of marijuana in Illinois, just like any other controlled substance. If the officer believes you are under the influence of marijuana they will administer a field sobriety test which will check and monitor your behaviors. If you fail this test you will be arrested and charged with a DUI or some equivalent. Marijuana is treated roughly the same as alcohol.
Law enforcement officials would love to have a clear way to tell when a driver is too drugged to drive. But the decades of experience the country has in setting limits for alcohol have turned out to be rather useless so far because the mind-altering compound in cannabis, THC, dissolves in fat, whereas alcohol dissolves in water.
And that changes everything. “It’s really difficult to document drugged driving in a relevant way,” says Margaret Haney, a neurobiologist at Columbia University, “[because of] the simple fact that THC is fat soluble. That makes it absorbed in a very different way and much more difficult to relate behavior to, say, [blood] levels of THC or develop a breathalyzer.”