There is no reliable way to chemically measure intoxication from marijuana. All the tests show is the presence of THC in the system. Hair tests can detect use as far back as 6 months, urine tests for 3 weeks, blood tests for 72 hours (typically used in accident investigations). Saliva tests, having a shorter duration of ~12 hours would be more ideal, but have an effectiveness cutoff of 50ng. The current legal limit in CO and WA is 5ng.
All that said, there's little correlation between the amount of THC in one's system and the level of intoxication. A chronic user (no pun intended) will have a much higher concentration of THC in their system and be affected less by it as compared to say, a tourist coming in and trying it for the first time in 20 years.
All that said, there's little correlation between the amount of THC in one's system and the level of intoxication. A chronic user (no pun intended) will have a much higher concentration of THC in their system and be affected less by it as compared to say, a tourist coming in and trying it for the first time in 20 years.