Eli5 Why isn’t there a more accurate way to test for thc like there is for alcohol? Eli5
In: Biology
Figuring out what the number means is difficult.
Firstly, THC is only one component in cannabis. It’s really a chemical soup of related compounds that are there in varying quantities from strain to strain. THC is thought to be the most psychoactive component, but it’s not the only one.
Secondly, THC and related compounds impact different people in different ways. It has been difficult to find a single threshold number where most people will be impaired.
Thirdly, THC doesn’t get eliminated from the body the same way that alcohol does. It can stick around for weeks or months and dissolves into body fat. This means that when you measure a certain level of THC in the blood, you don’t know for sure how much is actually in the brain.
Lastly, the degree to which THC (and related compounds) impair driving isn’t consistent between people or in the same person over time with repeated use.
With alcohol, there is a specific and well understood rate of elimination in people. So if they take two timed measurements in a police station they can reliably extrapolate what a blood alcohol level would have been when a driver was on the road, and reliably infer that the alcohol got there because the person consumed it, and that they were impaired to a level that was unsafe.
This isn’t as easy with cannabis and THC.
To be fair, we don’t really have a reliable way to do alcohol tests in the field either. The test that’s getting used against you in court isn’t the breathalyzer, but the blood test performed back at the station. The handheld units aren’t quite as reliable as we’d like them to be.
A blood test will give an accurate reading of active THC at the time the sample is drawn and will differentiate between active and metabolites. The problem is they’re invasive, expensive, and the results are relatively slow in comparison.
I believe some less invasive active THC tests are being developed.
There isn’t much thc in your blood compared to alcohol. It’s like trying to look at atoms with a microscope built to see bacteria.
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