Combinations of Ethanol and Prescription Drugs While Driving: Factoring Out the Effects of Ethanol

Presented at the American Academy of Forensic Sciences February 19, 1999, Orlando, FL

The combined pharmacologic effects of prescription drugs with CNS depressant actions and their interactions with ethanol can cause impairment of an individual’s ability to safely operate a motor vehicle. Operators of motor vehicles may not have been fully informed of the effects of their prescription medications on driving by their physicians, which may predispose them towards operating a motor vehicle unsafely. When ethanol has also been consumed, impairment may be greater than one might predict from the additive effects of ethanol and medication alone. In the Commonwealth of Massachusetts (COM), OUI ethanol and OUI medications are two separate charges which may be brought against an operator stopped by law enforcement for apparent unsafe operation of a motor vehicle. In COM v. Stathopoulous, 401 Mass. 453 (1988) 517 N.E.2d 450, the MA Supreme Judicial Court (SJC) clearly annunciated that the standard required to “prove” OUI ethanol was that the “liquor diminished the defendant’s capacity to operate a motor vehicle safely”. Therefore, in the courtroom, separating the effects of ethanol from the effects of prescription medications is critical to helping the jury reach a correct verdict regarding the alleged charges. This author presents an approach to factor out the effects of ethanol from those of concomitant ingestion of prescription medications.

Facts of the case: CH was a 32 year old white female, 5’4”, 120 lbs., with an established history of a bi-polar psychiatric disorder. On the day she was stopped, her medication and ethanol-ingestion history was as follows: 11am – lithium, 300 mg, nortriptyline, 50 mg, (non-impairing beta-blocker and thyroid medication); 7:30 pm – one “Pete’s Wicked Ale”, 8:30 pm – one “Pete’s Wicked Ale”; 8:45 pm – lithium,600 mg and nortriptyline 50 mg. Based on CH’s height and weight and using the “EZ ALC” computer program, utilizing the Widmark formula, this author was able to calculate a reasonable estimate of CH’s BAC at 10:05 pm , the time she was stopped by local law enforcement. This estimate was based on the fact that according to the manufacturer, Pete’s Wicked Ale contains 4.2% ethanol (w/v), and that each container of Ale contained 12 oz. to yield a total volume of pure ethanol of 0.50 oz. per container.

CH had just begun taking nortriptyline three days prior to having been stopped.. All other medications had been taken for some time. The half-life of nortriptyline is greater than 12 hrs., indicating that blood levels would be increasing for at least 6 half-lives, or 3 days. CH testified that on the day she was stopped, at approximately 3:30 pm , she had experienced “dry mouth, ringing in the ears, and dilated pupils”, all side effects of nortriptyline or lithium. The manufacturer’s professional information for nortriptyline published in the 1998 Physicians Desk Reference (PDR) listed the following side effects: confusional states, disorientation, incoordination, ataxia, dry mouth, drowsiness, tinnitus (ringing in the ears), and mydriasis (dilated pupils). The labeling also warned that nortriptyline “…may impair the mental and/or physical abilities required for the performance of hazardous tasks, such as operating machinery or driving a car…” and that “Excessive consumption of alcohol in combination with nortriptyline may have a potentiating effect….” However, since a BAC of less than 0.03% was not sufficient to produce impairment, two beers were not “excessive”, and CH was experiencing side effects attributable to her prescription medication throughout the day, the jury found her Not Guilty.

Various authors (1, 2) have published reliable data indicating that ethanol has only slight or negligible effects on behavior at BACs below 0.04%. Therefore, this author recommends that in order to factor out the effects of ethanol from those of contemporaneously consumed CNS-active drugs, one must first estimate the subject’s BAC. Based on the instruction of the COM’s SJC, since a BAC of less than 0.04% is too low to diminish an individual’s capacity to operate a motor vehicle safely, when the subject’s behavior is consistent with impairment, then the contribution of adjunctive medications should be considered as an alternative to an effect from ethanol.

Lastly, physicians, pharmacists, and other health care professionals need to intensify their efforts to warn their patients receiving CNS depressant medications of the dangers associated with using machinery and/or driving, especially during initiation of medication therapy and following dosage increase. This type of warning, as well as a precaution about the concomitant ingestion of ethanol, can greatly decrease the likelihood that a patient will operate a motor vehicle unsafely and be subject to an inadvertent accident or arrest for OUI ethanol/drugs.


1. Alcohol and the Impaired Driver, Chapter II, Acute Alcohol Intoxication, American Medical Association, 1968.

2. Dubowski, KM: Alcohol Determinations in the Clinical Laboratory, Am. J. of Clin Pathology 1980;74:749.