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Driving While High Law Starts Up

As of October 1st, anyone caught driving with more than five nanograms per milliliter of THC in their blood stream can be charged with a DUI in Montana. This mirrors laws already on the books for alcohol levels in the blood as an indication of intoxication. There’s one serious problem though – there isn’t a recognized scientific consensus as to the numerical relationship between THC (the active ingredient in marijuana) levels and intoxication.

According to a story in the Missoula Independent, the National Highway Transportation Safety Administration says, “It is inadvisable to try and predict effects based on blood THC concentrations alone, and currently impossible to predict specific effects based on THC-COOH concentrations.”

Still, our law at least attempts to set a level. Other states have opted for a zero tolerance policy, where any detectable level, along with police observations of erratic driving, can mean an arrest. Problems arise when a driver has a state-issued medical marijuana card. They are allowed to use the drug legally based on a doctor’s recommendation, but must still be sober enough to operate a motor vehicle safely.

As of this writing, the law hadn’t yet been tested in court, but actually proving a certain blood level of THC may not be needed to prosecute a case. For example, if a driver refuses testing for alcohol, they can still be charged. The default is to rely on police dash camera footage and the observations of the officer at the scene. Drivers can already be found guilty without chemical testing as evidence.

Setting a standard blood level will make some prosecutions easier, but also help clear other defendants who do not have high blood levels of THC. A blood test is considered a better measure than a urine test for marijuana use because it gives a “real time” reading, whereas urine can accumulate over many hours in the bladder.


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