Will Saliva Testing Lead to Accurate THC Readings in Future DWI Drugs Cases?

Posted by Doug Murphy | May 29, 2020 | 0 Comments

In Texas, law enforcement aggressively pursues charges of driving under the influence of marijuana. Despite this aggressive approach, there are major problems with establishing intoxication in a marijuana DWI case. There are substantial problems with obtaining an accurate reading of a driver's blood alcohol concentration, but those issues pale in comparison to the difficulty of testing a driver for marijuana intoxication. A saliva-testing system under development in a Texas lab the state hopes will be a viable form of testing for marijuana DWI cases.

The problem with the current system involves the length of time marijuana can remain in a person's system. Many tests can identify remnants of marijuana in your system, but these tests cannot identify if you are under the influence of the drug.  In fact, some tests cannot determine if you have imbibed marijuana recently.

THC Levels and Intoxication

Another problem with investigating a marijuana DWI case is that the science is not clear on what level of tetrahydrocannabinol (THC) constitutes impairment. Scientists disagree, with some suggesting as low as 1 nanogram of THC per millimeter of blood could lead to intoxication. Other researchers have found that 15 nanograms of THC should be the standard.  The leading researchers indicate that no per se drug level can be set based upon scientific research and that any per se level set is purely political, not scientific.

The saliva-testing system under development has had early success in identifying THC in human saliva. According to the creators of the device, it has accurately identified as little as 100 picograms of the substance.

The tests are unique in that they measure the level of THC in a person's saliva using an electrical current. The device requires sensor strips with the subject's saliva on it. The strips each have two electrodes coated with an antibody that will bind THC. This allows the strips to isolate the THC from the other substances within human saliva. The testing strips are then placed into the device, which sends an electrical current through the strip. Because the THC is isolated, the researchers can measure how the electricity interacts with the THC. This allows them to measure the amount of THC within the saliva in a way similar to how a diabetic person would measure their blood sugar level.

While allegedly accurate, there is an important detail that leaves these results in question. Because marijuana is illegal in Texas, the lab doing this testing has been unable to test the strips on a person that has used marijuana recently. Instead, the researchers have been limited to mixing THC into a saliva sample and then measuring it. This raises obvious questions on whether or not the tests will be as accurate on real samples.

The Impact on Your DWI Case

There is no guarantee this device will ever play an important role in DWI investigations. Even if it does, these cases will remain defensible. The state faces a high burden when it comes to proving their case, and a Board Certified expert in DWI defense lawyer can show all the holes in their case. By aggressively fighting back after an arrest, you could prevail at trial and avoid a conviction entirely.

About the Author

Doug Murphy

Doug Murphy is one of only two Texas lawyers Board Certified in Criminal Law by the Texas Board of Legal Specialization, and also in DWI Defense by the National College for DUI Defense, accredited by the American Bar Association and the Texas Board of Legal Specialization.


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