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Medical Marijuana & DUI Law


When the Illinois medical marijuana law went into effect on January 1, 2014, it resulted in necessary changes to Illinois DUI law to account for the fact that certain persons could now legally use marijuana for medical purposes. It is important to understand the impact of these changes.

Under the law, Illinois allows persons with certain medical conditions to use medically prescribed marijuana to alleviate the symptoms associated with those conditions. These include such medical conditions as cancer, arthritis, glaucoma, multiple sclerosis, Parkinson’s, spinal cord injuries and brain injuries, limb pain and post-concussion syndrome.

A person who is granted a registration card (known as a registered user) allowing him or her to use medical cannabis is granted immunity from local or state laws prohibiting the possession or use of marijuana in prescribed amounts.

Illinois prohibits a driver from operating a motor vehicle while under the influence of a drug or combination of drugs (including marijuana). The fact that a person is a registered user and therefore permitted to use medical marijuana is not a defense to a charge of DUI if impaired at the time of driving. The law also prohibits having a person from having a concentration of 5 nanograms of the active metabolite of marijuana in his or her bloodstream or 10 nanograms in any other bodily substance (e.g., urine, saliva) within 2 hours of driving or being in physical control of a vehicle.

However, if the person is a registered user who can legally use medical cannabis, these limits do not apply to that person, again unless impaired and under the influence.

However, the registered user gives up certain rights in exchange for receiving immunity under the law. Currently, under Illinois law, a person under investigation for DUI is not required to submit to what are known as standard field sobriety tests when asked by a police officer. These are also known as physical performance tests and include the walk and turn test, one-leg stand test and horizontal gaze nystagmus test. Under the law, there is no driver’s license or other penalty for refusing field performance tests or taking and failing the tests.

However, in exchange for permitting the medical use of marijuana, a registered marijuana user must submit to these tests if the officer has a reasonable suspicion that the person is driving under the influence of cannabis. A person who fails testing or refuses testing is subject to the summary suspension or revocation (in the case of an accident involving serious injury or death if testing is refused) of their driving privileges. Persons who are not registered users continue to have no obligation to submit to testing and there is no license penalty for refusing or failing testing.

Registered users who submit to field sobriety testing and fail or refuse testing are prohibited under the law from applying for a monitored device driving permit (MDDP). Non-registered users who fail or refuse testing continue to be eligible for such permits.

If a registered user submits to and fails testing then he or she is subject to a 6-month summary suspension of their driver’s license. Those who refuse testing are subject to a 12-month summary suspension.

Registered users who hold Commercial Driver’s License (CDL) holders are subject to a 12-month disqualification (or lifetime disqualification in the case of a second offense) if he or she submits to and fails field sobriety testing or refuses testing. Just as with regular driver’s license holders, there is no disqualification penalty for CDL holders who are not also registered users if field sobriety testing is refused or failed. CDL holders should remember that this law applies whether he or she is operating a commercial or non-commercial motor vehicle.

The law also provides that a registered user may not use marijuana while in a vehicle upon a public highway (whether as a driver or a passenger). It also provides that marijuana may not be transported within the vehicle unless it is in an approved tamper-evident container.


Anyone who plans on becoming a registered user must remember that being granted legal permission to use marijuana to alleviate the symptoms associated with a serious medical condition is not a license to drive while under the influence. Furthermore, for those who attempt to do so, the consequences are potentially even more severe than for those who are not registered users.

The attorneys at The Davis Law Group, P.C. have extensively studied and identified many issues under the new law. We anticipate that there will be further revisions in the law in the near future. Attorney Larry A. Davis of The Davis Law Group, P.C. is not only a co-author of the law, but has also written and lectured on it. Let us put our knowledge and experience to work for you.

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