Marijuana DUI: How Long Does Marijuana Stay in Your System

We’re seeing it more and more in King County—arrests for marijuana DUIs. The other day, there was another article about it in the Seattle Times. What caught my interest about this particular article was something that the driver said to the police officer. Apparently, the driver admitted he had smoked weed but also explained to the officer that it was no big deal because now that weed is legal, he could smoke as much as he wanted.

Perhaps that’s true, but he just can’t get behind the wheel of a car! It got me thinking and wondering about how many people are aware of the effects of marijuana and how long it stays in your system.

As a lawyer, I’ve had many people ask me questions in the last few months about marijuana and DUIs.

When recreational marijuana was legalized in our state in 2012, the provision came with very tough DUI standards. While you can legally possess up to an ounce of marijuana, it is illegal for you to drive if your THC blood content is over 5 ng/ml. Urine and blood tests are both used to determine the amount of marijuana in your system, but for DUIs, blood tests are specifically used. In general, the more visible effects of weed fade relatively quickly in a couple of hours.

Effect On Driving

Cannabis intoxication does mildly impair motor skills but those effects are not long-lasting or necessarily severe in most cases. In driving simulator tests, drivers have been shown to have longer reaction times in response to emergency situations, and also to have a tendency to drive much slower. Drivers seem to not only be aware of their impairment, they try to compensate for it by slowing down and focusing on the road more. Alcohol-impaired drivers have the opposite reaction; they tend to drive in a riskier fashion.

THC In Your Blood

Unfortunately, the THC metabolites that are left behind do linger in the body. There are over 80 metabolites that are stored in your fat cells. Some metabolites have a half-life of 20 hours, while some can stay in your system 2 weeks or longer. It’s important to know that it takes five-to-six half life cycles for THC to be completely eliminated from your system. Some research studies have shown that marijuana users have traces of THC metabolites for as much as 45-90 days afterward – so you can see that they can stay in your system for quite some time, and are gradually eliminated through feces and urine. This is why urine tests are very effective in testing for marijuana.

Additionally, there are so many other factors that affect how long marijuana stays in your bloodstream. The more body fat you have, the longer THC stays with you, and your eating habits and your activity levels are also factors. The frequency of ingestion and the method of delivery matter too. THC goes out of your system fairly quickly when you smoke, while other methods like ingesting edibles take longer to enter your blood, usually about a half hour.

Everyone’s different. People have different metabolic rates, and their bodies process THC at different rates. A study by the National Highway Safety Administration showed that marijuana can impair driving for up to three hours. Some effects can last up to 24 hours. In terms of a blood test, THC can be detected for a few hours afterward.

When it comes to knowing how long marijuana stays in your system, the bottom line is this: all that variability we just covered means it’s impossible to know or predict with any degree of certainty under what conditions or when someone would test positive. So, err on the side of caution and don’t drive. If you do get stopped for suspected DUI, your blood test is going to depend on all of these factors.