Missouri voters recently passed Amendment 3, legalizing the personal use of marijuana. Driving under the influence of marijuana is still illegal. Unfortunately, the procedures and criteria for identifying impairment are not perfectly established. This uncertainty puts users in a difficult position.

Missouri Alcohol Intoxication Law is Well Established

Missouri law holds that a blood alcohol content of .08% or above is sufficient proof of a driver's intoxication. It is rare to see someone charged with DWI absent a failed BAC test or a refusal to take the test. The field sobriety tests that officers have people perform during DWI traffic stops are done to assess whether or not a BAC test is warranted. 

In other words, a test to determine blood alcohol level, usually by breath, is the crux of a DWI case. 

Missouri Marijuana Intoxication Law is Not As Well Established

A “gold-standard” test for marijuana intoxication does not currently exist. Some states have attempted to establish a per se level of THC metabolites in a person's blood comparable to the .08% used in alcohol DWI. This level is most commonly 5 ng/mL of Delta-9 THC. Some states use 2 ng/mL. Missouri does not have a per se limit, but a blood test with a 5 ng/mL reading or higher will give law enforcement and prosecutors ample evidence to claim marijuana intoxication. 

The problem with that level, according to a study in Nature, is that approximately half of all regular users will have a reading of at least 5 ng/mL before smoking (12 hours of abstinence). Over 80% had a level over 2 ng/mL. 

In other words: the majority of habitual marijuana users will fail a marijuana intoxication blood test even when sober. All take to get a DWI is to get pulled over, make a few mistakes on field sobriety tests, and then fail the blood test. 

The reason marijuana blood testing for intoxication is so inefficient is that Delta-9 THC levels spike immediately after smoking and then fall rapidly. Typically, the concentration is above 50 ng/mL for 10 to 20 minutes, then drops below 20 ng/mL by 30 minutes. The level is usually about 10 ng/mL by around an hour and slowly wanes after that. 

The problem for law enforcement is that they rarely get a chance to test someone within an hour of smoking. Even if they catch someone in the act of driving and smoking, the field sobriety tests and transport to the hospital for blood testing will still take over an hour. From what I have seen, they are lucky to get a blood test within two hours of pulling someone over. By that time, levels have drifted down to baseline or slightly above. 

Field Sobriety Tests for Marijuana Intoxication

No problem, you think; I will not fail the roadside tests if I am sober. Unfortunately, it is not that easy. The idea for this blog post came after watching a Youtube video of a young man being falsely arrested for marijuana DWI. He was driving with one headlight out, so the police officer had a legitimate reason to pull him over. The young man had a very relaxed attitude that the officer clearly took to be a sign of marijuana use. 

The real problem occurred when the guy failed his field sobriety tests. The first test was for eye nystagmus. Nystagmus was not apparent in the video, but the officer saw it (even though the kid was sober). Make of that what you will. When the officer had the young man do a walking and a standing test, he was not able to follow instructions. By the well-established standards of those tests, they were absolutely failing efforts. Fortunately, he was a college athlete and showed a long streak of clean weekly drug tests.  

The efficacy of alcohol field sobriety tests in assessing marijuana impairment is a subject of much debate. As you can see, it is possible to fail them when sober. They are meant to be used as a tool to determine if further testing for BAC is necessary. Marijuana-specific roadside sobriety tests are probably even less effective. Most officers do a test to determine if you can estimate how long 30 seconds is and a test to see if you can cross your eyes. More than 10% of people will fail these tests even when sober. 

Some police officers are qualified as Drug Recognition Experts (DRE). They take 100 hours of training to be able to conduct a 12-step evaluation that lasts over an hour. Approximately 1% of officers have this qualification. If you get pulled over, it will not be by one of these officers. You will be pulled over by an officer who has training in DWI field sobriety tests and maybe knows the additional tests for marijuana intoxication evaluation. If you are too tired or nervous to follow instructions, have trouble estimating 30 seconds, or can't cross your eyes, you might be asked to take a blood test. If you are a regular user, you have a 50/50 chance of testing high. 

The Bottom Line

Regular marijuana use puts you in a position where you can fail a blood test, even if you have not used in days. Evaluating marijuana intoxication is not as straightforward or precise as measuring alcohol intoxication. Marijuana users will be in a vulnerable position until the science and law catch up.

If you find yourself in the unfortunate position of being accused of a marijuana DWI, please call Attorney Ruth Beerup at 636-940-1111. She has experience handling cases like yours and can fight for the best outcome possible.