DWI by Alcohol and its Synergistic Effect with Another Substance

Last week I wrote a post on the kind of evidence needed in a DWI by drug case. There's another related situation worth mentioning-when the driver consumes a substance (be it an over-the-counter medication or a controlled substance) that makes him more susceptible to the effects of alcohol. This is referred to as the "synergistic effect" of alcohol and a consumed substance or drug. In such a case, the prosecutor can argue that despite a breath test result below the legal limit, the driver was nevertheless intoxicated because a consumed substance made him more prone to the effects of alcohol.

Many clients find this a startling revelation-the idea that you can blow under the legal limit and yet still be convicted of DWI by alcohol. The reason of course, lies in the fact that along with a .08 breath test score, Texas law defines intoxication as the loss of normal use of physical or mental faculties. Alcohol and some other substance, the argument goes, has enhanced the effect of the alcohol resulting in intoxication. Texas courts consider a person found guilty of DWI by reason of the "synergistic effect" to be intoxicated exclusively as a result of alcohol. 

The "synergistic effect" theory differs, however, from a claim that alcohol combined with a drug or substance caused intoxication. This fine distinction used to matter before the Texas Court of Criminal Appeals changed its mind about what constitutes the "elements of the offense" of DWI. That's getting pretty technical and I mention it simply to make you aware of the "synergistic effect" theory of prosecution.

Can the prosecutor make the same type of argument about a bodily condition that has weakened you and increased the effects of the alcohol-say for example, fatigue? The "synergistic effect" theory does not apply to fatigue, or any other purely natural deterioration of the body. "Synergistic effect" applies to alcohol and its interaction solely with substances.

As is the case with DWI "by drugs", the prosecutor needs expert testimony to establish the synergistic effect of alcohol and a substance, though no Texas case explicitly says so. The logic of the Smithart decision (discussed in last week's post) readily applies.

So if alcohol and some other substance are involved in your case, watch out-just because you've got a breath test result under the legal limit doesn't get you off the hook if an argument can be made that something you took-an antihistamine, a prescribed muscle relaxant, etc. made you more susceptible to the effects of alcohol.