Although some states have legalized the use of marijuana, it is still illegal to drive under the influence of marijuana in Texas and across the country. Despite the wording of the law, it is much more difficult to prove a marijuana DUI compared to one involving alcohol.

With alcohol intoxication, a breathalyzer is the most common tool used to determine if a person is under the influence. A breathalyzer works by measuring alcohol molecules in the breath and using that data to determine blood alcohol level. The technology works because researchers have a clear understanding of the relationship between blood alcohol and alcohol in the breath.

The same is not true about marijuana. It is still not clear what the relationship is between THC measured in the breath and the amount found in the blood. Researchers are focusing efforts on THC’s vapor pressure, which is vital to understanding the connection between breath and blood concentrations. While an actual workable machine is yet to be developed, the researchers hope to lay the technical groundwork for one.

Without a reliable roadside test of determining marijuana impairment, police may rely on less specific methods. These may be called into question in court. Examining how the officers determined a driver’s level of impairment and if the judgment was fair and valid according to the law could have a major impact on DWI defense related to marijuana. It may be possible that the results of a test are inadmissible if they are deemed too inaccurate. A criminal defense attorney may be able to answer a client’s questions regarding tests and how they affect the case.