That link doesn't appear to say that blood tests are reliable

Literally in the summary

> While blood alcohol content (BAC) level represents an accurate measurement of alcohol impairment, the presence of THC in a driver’s body has not been shown to be a predictable measure of cannabis impairment.

But further on

> Because THC in the blood can result from both recent as well as past use, impairment cannot be inferred from blood levels.

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nobodyandproud a day ago | parent [-]

That’s not the relevant bit. A blood test detects recent use of THC.

Which other, less invasive methods cannot. Like alcohol, impairment is highly individual and so we set a threshold.

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squigz a day ago | parent [-]

It is not a reliable indicator of recent use though, since it can also indicate past use.

I agree we need to set a threshold for impairment. I just want that to be measured reliably so that people who had a brownie last weekend aren't getting in trouble.

	▲	nobodyandproud a day ago \| parent \| next [-]
		Driving isn’t a right. No matter how steeped the US is in car culture, it’s important not to lose sight of this. Now blood tests show a 12-24 hour window of usage. Much tighter than the 2 to 30 days of other tests. In terms of window of time, that’s essentially good-enough. Of course anyone who consumes cannabis has a strong desire for a tighter and more accurate test, but you’re really fighting against growing masses of irresponsible users. If the problem is truly wide-spread like alcohol was (and still is), it’s just a matter of time before states or feds push for a good-enough (for the rest of us) solution.
	▲	reactordev a day ago \| parent \| prev [-]
		THC leaves the bloodstream within 24 hours just to be clear. I know this is a giant hairball and the downvotes and passionate discussion is why I said what I said but in the end, until we have a breathalyzer for THC, it is what it is.