In Texas, someone can be charged with driving while intoxicated whether they are intoxicated from alcohol, marijuana, or some other intoxicating drug. Most people know that the legal limit for alcohol is a blood alcohol content (BAC) of .08 or higher. What many people don’t know, is that there is no magic number for marijuana.
In some states, like Colorado, you are above the legal limit if you have .05 nanograms of active THC or higher. Thankfully, Texas has not taken this approach. The National Highway Traffic Safety Administration (NHTSA), which is the agency that has developed and trained officers on the Standardized Field Sobriety Tests for alcohol, has determined that there is no direct relationship between a person’s level of THC in their blood and the level of intoxication they are feeling. NHTSA’s report Marijuana-Impaired Driving, A Report to Congress states, “the poor correlation of THC level in the blood or oral fluid with impairment precludes using THC blood or oral fluids as an indicator of driver impairment.”
Just because Texas does not have a legal limit for marijuana, does not mean that it’s legal to drive after smoking. Under Texas law, there are two other ways to prove that you are intoxicated: 1) if you have lost the normal use of your mental faculties because of an intoxicant or 2) if you have lost the normal use of your physical faculties because of an intoxicant. In alcohol related cases, the standardized field sobriety tests are supposed to help with these two. I don’t think they are as effective at determining whether a person is intoxicated on alcohol as NHTSA says they are, but there is at least some research that supports them. What that research does not show is any relationship between performance on field sobriety tests and intoxication from marijuana use.
A separate test was developed that was supposed to determine when a person was intoxicated due to drugs and what type of drug was causing their intoxication. Some officers went through training to learn how to perform these tests and be certified as drug recognition experts. There are currently only a few officers qualified to perform them. So few that I have never had a client that has gone through these tests. Instead of three tests like the field sobriety tests, there are 12 tests to determine drug intoxication. Unlike the field sobriety tests, these tests cannot be performed at the roadside easily, there is no research that validates these tests, and they are so complicated for an officer to administer that there were often mistakes made by the officers.
Of the three ways that the state can prove intoxication, none of them is particularly easy for the state to prove that a person is high after smoking marijuana. Drivers that are arrested often help the state out by admitting to recently smoking to the officer, performing roadside tests, or having a combination of marijuana and alcohol in their system.
I always advise people, particularly if you have had anything to drink or smoke, once an officer starts asking about drinking or drug use, ask for an attorney and then remain silent. You have those Constitutional rights and you should use them. The officer is asking those questions because he believes that you may be intoxicated, and he is trying to get information that supports that belief. This frequently leads to arrest and could lead to a conviction.