Synergistic Effects of Drugs and Alcohol

What happens when the prosecutor has evidence that the driver is under the influence of several different drugs or a combination of a drug and alcohol even when any one of those substances would not necessarily be enough to prove impairment?

When two or more drugs are taken in combination, the prosecution will often argue that the effects are multiplied or enhanced. Alcohol can also increase the negative side effects of a drug or drugs in the system.

The state will often present testimony about the "synergistic effects" of taking drugs and alcohol on a person's physical and mental faculties, especially when the blood or breath alcohol concentration (BAC) at the time of testing is at or below .08.

Attorneys for the Synergistic Effects in DWI in Fort Worth

The attorneys at Law Offices of Richard C. McConathy are experienced in dealing with cases involving allegations of impairment by the combination of alcohol and drugs. Call a Fort Worth DWI attorney to discuss the facts of your case, the penalties that can apply, and the best ways to fight the case for the best possible result.

Call (817) 422-5350 today.


Factors for DWI Impairment by Drugs and Alcohol

In determining whether there is sufficient “other evidence” in the record to support a finding of intoxication, the court will look at a variety of factors including:

  • whether the defendant admitted to consuming alcohol or other intoxicating substances prior to driving;
  • whether the defendant appeared intoxicated at the time of his arrest; and
  • whether the nature of the accident suggested that the defendant was intoxicated.

In Crenshaw v. State, 378 S.W.3d 460, 467-68 (Tex.Crim.App. 2012), the court found that the evidence was sufficient to support a finding of intoxication under an impairment theory where the defendant's BAC level was 0.07% at time of blood draw, which together with other evidence of the defendant's intoxication, including his appearance at the time of his arrest and his admission that he drank and smoked marijuana prior to driving, made it “more probable that Appellant was subjectively impaired at the time he was driving, thereby supporting the theory alleged in the information and applied to the facts in the charging instrument."

In many of these cases, the prosecutor will ask the court to instruct the jury on the synergistic effects of narcotics and alcohol. Such instructions are deemed a proper application of the law to the facts of the case when the evidence demonstrates the defendant ingested multiple substances prior to driving. See Gray v. State, 152 S.W.3d 125, 128, 133-34 (Tex.Crim.App. 2004).


DWI with a Combination of Alcohol and Other Drugs

According to the Breath Test Operator Intoxilyzer 5000 Manual, when ethyl alcohol is consumed in combination with other chemical agents, illicit, prescribed, or over-the-counter, the symptoms of alcohol intoxication may be altered. This may explain the situation where an individual appears very intoxicated, but the alcohol test results are low.

Combining ethanol with other drugs can produce two types of effects: additive or synergistic. When one dose of a drug is combined with one dose of ethanol and the effect is equal to no more than the sum of the effects of the two drugs, the effect is said to be additive. 

A synergistic situation occurs when a drug is combined with ethanol and the end result is greater than the sum of the individual effects. There is no known drug that can lessen the effects of ethanol on a person’s driving performance.


This article was last updated on Monday, April 24, 2017.