What is the half life of THC, how does it affect DUI laws in CO or WA

I can’t find info on the actual half life of THC for some reason, but I know the effects of marijuana tend to wear off after a few hours so I am assuming the half life is about 30-120 minutes. The info I’m seeing is saying stuff like 20+ hours. That can’t be accurate, if it were then whenever people smoke marijuana they’d be high for days instead of hours.

However I know the half life of metabolites in the body is 1-2 days, possibly longer. Since states like Co and Wa have legalized marijuana there are efforts to have more DUI enforcement. So how do they distinguish between actually being impaired vs just having metabolites from using drugs several days ago?

Blood tests seem pretty invasive and like a big hassle. A urine test could show that someone smoked marijuana 8 days ago despite the drug wearing off in hours after they originally used it. What exactly do they do to determine impairment? I’ve heard saliva tests, but have no idea.

The standard for a DUI in Colorado is 5 nanograms of THC per milliliter of blood, and it is done via a blood sample. They can’t really tell if you are still high or not, so unless the car is filled with smoke or you’re giggling like a madman, they aren’t going to take you in for a blood test.

Personally. I think this is one of the reasons more states haven’t legalized it.
They haven’t found a practical way to test if you’re high or you just have it in your bloodstream.
As soon as they find a good way to arrest you for using it, they’ll legalize it.

They need to come up with a saliva or breathalyzer test to detect blood thc levels. Someone’s probably working on it, but the field is probably still open.

There IS a saliva test. There are several, in fact. Most of them are modified urine tests, which test for the metabolites in the saliva, and therefore detect use in the past 20 days or so. But there is also at least one test that detects THC, not the metabolites. I have no idea why no one knows about it. I suspect it’s intentionally not talked about so that lawmakers can hide behind this myth that we can’t identify those driving under the influence of marijuana* to delay legalization.


*Just remember that it’s still pretty questionable as to whether having THC in your system is a good sign of impairment. “Driving under the influence of marijuana” is not so clearly dangerous as driving under the influence of alcohol. These tests may be valuable to law enforcement, but they are not generally endorsed by marijuana advocacy groups.

Of course, I presume that just because it’s legal, doesn’t mean that some employers won’t continue to fire people who test positive.

There is one, a saliva test. The police here (Queensland, Australia) use it, the results take about five minutes to come back. It’s not used as a routine thing the way Random Breath Tests are (pretty much any interaction you have with the police in your car will involve getting breathalysed here) but the Booze Bus (mobile RBT command centres) have the ability to to do it from what I understand.

My understanding is that in Colorado the tests primarially used to find the impaired are things like “walk a straight line” and “say the alphabet backward” types. If you lack physical mental coordination they can then ask for a blood test.

Keep in mind, determining DUI has never been just about a breathalyzer test. DUI is not and never has been restricted to alcohol, and if you’re found impaired due to, say, prescription drugs, even if legitimately taken, you can still be prosecuted.

Anecdotally, people subject to drug testing for employment purposes (especially in Australia’s mining industry) have replaced Marijuana (which, depending on the test, can show up positive weeks after taking/effects wearing off), with “harder” drugs like Methamphetamine. (“Party” in your time off. Pass the test the next day.)
I’m not sure anyone would think this is a desirable outcome.

Well, if I ever get pulled over, I guess I’m screwed, and I don’t even smoke…

Yeah, with urine tests marijuana can be detected for weeks (in some cases months if you are fat and a chronic user) while other hard drugs are out in 2-3 days.

But a hair test can detect the harder drugs for months while I dont’ think it detects MJ well. However I think most employers prefer the urine test, probably for price.