As Illinois prepares for the legalization of marijuana, police officers still don’t have a clear answer about how they will test for impaired driving. As of now, there is no reliable test to determine intoxication levels for marijuana. That’s because the standard tests that are used to measure alcohol intoxication don’t work in the same way for marijuana intoxication.

Police are admitting that marijuana-related DUI charges will have to rely heavily on what officers observe at the scene. Though officers may observe the smell of marijuana on a driver, they will be unable to use a breath test to measure the driver’s exact THC levels. A 2004 study showed that the field sobriety test commonly used for drunk drivers does not translate to high drivers, though standing on one leg did prove difficult for marijuana smokers.

Some of the behaviors that police officers may look for in marijuana-impaired drivers may be memory problems, inappropriate laughter and delayed reaction time. Driving without headlights on at night is another possible sign of marijuana intoxication as the drug causes pupils to dilate in light. Though a blood draw may be an effective test for marijuana, the results take several weeks to come back.

Illinois does not have a legal limit for what is considered marijuana intoxication. Since there is no legal standard for how much marijuana gets a person high, someone who is accused of being impaired by marijuana may argue that the charge is based on an opinion. A criminal defense attorney may be able to help an individual who is facing drug charges related to marijuana to defend his or her case in the new legal climate.