THC and DUI: How Illinois Measures THC as an Intoxicating Substance in DUI Cases

With the legalization of recreational cannabis in Illinois, the landscape of DUI cases has changed, introducing new challenges in identifying and prosecuting drivers impaired by THC, the psychoactive compound in cannabis. As personal injury lawyers at John J. Malm & Associates, we’ve seen firsthand how dangerous impaired driving can be—not only for the drivers involved but also for the innocent victims of these accidents. When a driver under the influence of weed causes an accident, it can have devastating consequences, often leaving victims with severe injuries, emotional trauma, and financial burdens.

Understanding how THC is measured and handled in Illinois DUI cases is critical for victims seeking compensation. In this blog, we’ll explore the methods Illinois law enforcement uses to assess THC intoxication, how it affects DUI car accident cases, and the impact of cannabis-impaired driving on personal injury claims.

Illinois DUI Laws and Cannabis Legalization

Since January 2020, Illinois has legalized the recreational use of cannabis for adults 21 and over. With this change, the state also had to update its DUI laws to include cannabis-related impairment. Just like with alcohol, it is illegal to drive under the influence of pot if it impairs your ability to operate a vehicle safely. The Illinois Vehicle Code now includes provisions for driving under the influence of cannabis (DUI-cannabis) and other intoxicating substances, such as gummies, making it clear that drivers who are impaired by THC can be held accountable for the accidents they cause.

For victims of THC-impaired driving accidents, these laws provide a basis for pursuing personal injury claims. However, the complexities of measuring cannabis impairment present unique challenges in proving negligence in DUI-related injury cases.

How THC Impairment Is Measured in Illinois DUI Cases

Unlike alcohol, which is easily measured through a blood alcohol concentration (BAC) test, THC impairment is much more difficult to quantify. THC affects individuals differently based on various factors, and it can remain in the body long after its intoxicating effects have worn off. Despite these challenges, Illinois has established several methods for measuring THC impairment in DUI cases.

1. Per Se THC Limit

In Illinois, a driver is considered impaired by cannabis if their THC concentration is 5 nanograms or more per milliliter of whole blood or 10 nanograms or more per milliliter of another bodily substance, such as saliva or urine. This per se THC limit functions similarly to the 0.08% BAC limit for alcohol and provides a legal threshold for intoxication.

However, this standard is not without controversy. The presence of THC in a driver’s system does not necessarily indicate impairment at the time of the accident. THC can remain in the bloodstream for days or even weeks after consumption, particularly in regular users, which means that a driver could exceed the per se limit without actually being impaired. For victims of accidents caused by drivers with elevated THC levels, this legal gray area can complicate personal injury claims.

2. Field Sobriety Tests (FSTs)

Law enforcement officers often use field sobriety tests (FSTs) to evaluate a driver’s level of impairment at the scene. These tests include activities like walking in a straight line, balancing on one leg, or following an object with the eyes, which are designed to detect impairments in coordination, balance, and focus.

While FSTs are useful for detecting alcohol impairment, their effectiveness in identifying cannabis impairment is limited. THC affects the body differently than alcohol, often impairing judgment or reaction times without visibly affecting physical coordination. This can make it difficult for officers to determine whether a driver is truly impaired by cannabis using FSTs alone.

3. Chemical Testing (Blood, Saliva, Urine)

After an arrest for suspected DUI-cannabis, law enforcement may request a blood, saliva, or urine test to measure THC levels in the driver’s system. Blood tests are considered the most accurate, but they are invasive and time-sensitive, as THC levels drop rapidly after cannabis consumption. Urine and saliva tests are less invasive, but they often detect THC metabolites, which can indicate past use without proving current impairment.

For victims of THC-related accidents, the timing and type of chemical testing can significantly impact the personal injury case. If the driver’s THC levels are high, it provides critical evidence of impairment. However, if there’s a delay in testing or if the driver is a regular cannabis user with residual THC in their system, proving intoxication at the time of the accident may be more challenging.

The Challenges of Proving THC Impairment in Personal Injury Cases

From a personal injury perspective, THC impairment presents a unique set of challenges when pursuing compensation for victims. Unlike alcohol, where impairment can be more easily established through BAC tests, THC’s effects vary widely from person to person, especially with how it is consumed, i.e., edibles, gummies, smoked, etc. Some of the key challenges include:

1. Individual Tolerance and Usage Patterns

Cannabis affects people differently based on their tolerance, frequency of use, and method of consumption (smoking, edibles, vaping). A regular user may have a higher baseline level of THC in their system, but this doesn’t necessarily mean they are impaired at the time of the accident. As a result, proving that the driver’s THC levels caused their impairment can be difficult.

2. Delayed Testing and THC Metabolites

The timing of chemical testing can also complicate personal injury claims. THC levels drop rapidly after use, so if there is a significant delay in administering a blood test, the results may not accurately reflect the driver’s level of impairment at the time of the crash. Urine and saliva tests, which detect THC metabolites, can only prove past cannabis use, not current intoxication.

3. Field Sobriety Tests and THC Impairment

As mentioned earlier, FSTs are not as reliable for detecting cannabis impairment as they are for alcohol. In personal injury cases, the results of these tests may not be sufficient to prove that the driver was impaired by THC at the time of the accident. This lack of clear evidence can make it harder to establish fault and hold the at-fault driver accountable.

Relying on Law Enforcement Evidence in THC-Impaired Driving Cases

In Illinois, when pursuing a personal injury claim against a driver impaired by THC, plaintiffs and their attorneys must rely heavily on evidence collected by law enforcement. Unlike alcohol-related DUI cases, where roadside breathalyzers or private BAC testing might be possible, there is no practical legal way for personal injury attorneys to independently obtain the critical evidence needed to prove THC impairment at the time of the accident. This makes the collection, testing, and documentation of evidence by law enforcement a crucial component in building a strong case.

1. Chemical Test Results

One of the most important pieces of evidence in a THC-related DUI case is the result of chemical tests, such as blood, saliva, or urine tests, administered by law enforcement. These tests measure the concentration of THC in the driver’s system and are key to establishing whether the driver exceeded Illinois’ per se legal limit of 5 nanograms per milliliter of THC in the blood.

As attorneys representing injured plaintiffs, we cannot conduct these tests ourselves. Instead, we rely on law enforcement officers to properly administer the tests in a timely manner and to preserve the results as part of the official record. If there are issues with the timing, method, or accuracy of the testing, it can weaken the case and complicate efforts to prove the driver’s impairment.

2. Field Sobriety Test Documentation

While field sobriety tests (FSTs) are not as reliable for detecting THC impairment as they are for alcohol, they still serve as important evidence in a personal injury case. Law enforcement officers trained to recognize the signs of impairment document their observations during the FSTs, including the driver’s coordination, balance, and focus. These observations can help bolster the claim that the driver was impaired at the time of the crash.

As attorneys for the injured party, we depend on the thoroughness of the police report and the officer’s documentation of any signs of impairment. Without this evidence, it becomes more difficult to demonstrate that the driver’s behavior was affected by THC, potentially undermining the strength of the case.

Attorney John J. Malm on the Dangers of Driving High

“Driving high can be just as dangerous as driving drunk. THC impairs judgment, reaction time, and motor coordination—critical functions necessary for safe driving. We’ve seen far too many cases where victims suffer life-changing injuries because a driver made the reckless decision to drive under the influence of cannabis. One of our clients, a young mother, was involved in a devastating head-on collision when a driver under the influence of THC veered into her lane. The crash took the life of her four-year-old daughter and left her with life-altering injuries. The emotional and physical toll is unimaginable, and this tragic case serves as a reminder of just how dangerous driving high can be.” – John J. Malm

Building an Injury Case Against a Negligent High Driver

As THC becomes more widely used in Illinois, the risks associated with driving under the influence of cannabis are increasingly recognized. While Illinois law provides clear guidelines for prosecuting DUI-cannabis cases, proving impairment remains challenging due to the complexities of measuring THC intoxication. For victims of THC-impaired driving accidents, these challenges can make it difficult to pursue personal injury claims.

We know that THC related claims are at the center of many car accident, truck accident, and wrongful death cases we handle. At John J. Malm & Associates, we have the experience and resources needed to navigate the complexities of THC-related DUI cases and advocate for injured victims. If you or a loved one has been injured in a DUI accident involving cannabis, contact the experienced Illinois car accident attorneys at John J. Malm & Associates for a free consultation.