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What Marijuana Users Need to Know to Avoid DUI

Posted on in DUI Drugs

Illinois defense lawyerAlcoholic beverage drinkers can easily determine when they have drunk too much to drive. They can consult a simple chart that estimates blood alcohol concentration (BAC) based on gender, weight, and how many standard drinks they’ve had. Unfortunately, such simple charts do not exist for marijuana. So how can medical cannabis users know when they are safe to drive in Illinois and not get charged with driving under the influence?

Under current Illinois law, a THC level over 5 nanograms per milliliter of whole blood is per se (sufficient by itself) proof of marijuana DUI for most drivers. Illinois medical cannabis cardholders are exempt from the THC limit, but they can still be charged with DUI based on other evidence of impairment, primarily failure on the standardized field sobriety tests (walk-and-turn, one-leg stand, and follow-the-object eye test).

This article provides a basic explanation of how the body processes THC, the psychoactive compound in marijuana associated with driver impairment, to help users understand how marijuana may affect their ability to drive.

How Marijuana Consumption Affects Blood THC Levels

The first thing cannabis users need to understand is how marijuana consumption is reflected in blood THC levels, to avoid testing over the legal limit (for drivers without Illinois medical cannabis cards).

When marijuana is inhaled via smoking or vaping, THC blood levels peak in about 10 minutes, often reaching levels over 50 or even 100 ng/ml, which would make a driver very impaired. Post consumption, blood THC levels quickly drop to single digits within one hour. Most experts say that infrequent users should allow at least four hours after a low dose for blood-THC to drop to a safe level and up to 24 hours for high doses. Frequent marijuana users will likely be over the legal limit at all times, unless they stop using for at least a week or more.

Cannabis edibles and topicals have a much different effect than inhalation. With edibles, THC blood levels peak about four hours after eating and decline to near zero about four hours after that. Topical use of cannabis oil has no psychoactive effect and thus poses no risk for DUI.

How Blood THC Levels Correlate with Driver Impairment

The second thing marijuana users need to understand is how blood-THC levels correspond with driver impairment. With alcohol, higher your blood-alcohol level, the more impaired you are. With marijuana, the correlation between blood-THC and impairment is not that simple.

There is no question that a high level of THC in the blood does affect brain functioning and motor skills, and therefore impairs driving. But how high is high? And how long does a driver remain impaired, even after their blood-THC falls below the Illinois legal limit of 5 ng/ml?

On one hand, scientists have shown that, when marijuana is inhaled, impairment of brain functioning lasts longer and declines more slowly than the THC level in the blood. Thus, an infrequent marijuana user can remain impaired for several hours after their blood THC level is below the legal limit.

On the other hand, a regular cannabis user may continuously have blood-THC over 5 ng/ml, yet demonstrate no mental or physical impairment. One reason for this is that THC can be stored in body fat and released back into the bloodstream at a later time, with no psychoactive effect. This is why Illinois does not hold its medical cannabis cardholders to a blood-test standard, but rather requires them to pass standardized field sobriety tests.

In the end, what can marijuana users do to avoid DUI? Medical cannabis cardholders must be primarily concerned with their ability to pass field sobriety tests. Other marijuana users must also consider the THC content of the product they use, frequency of use, and how long it has been since their last consumption, to avoid testing over the legal blood-THC limit.

Cannabis DUI Defense Attorney in Oak Brook

If you are charged with driving under the influence of marijuana in the Oak Brook area, you need to consult an experienced DuPage County marijuana DUI defense lawyer before making any decisions. The attorneys at McMahon Law Office will diligently investigate all the circumstances of your case and work aggressively to get you the best possible outcome. For a free consultation, call 630-953-4400.







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