How alcohol and drugs affect driving

Key points

1. By law, at least 25 percent of knowledge test questions cover drugs and alcohol.

   Source: Handbook p. 79

   “by law, at least 25 percent of the questions on the knowledge test must consist of questions dealing with this topic.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 79

2. Your liver can remove only about 1 drink per hour; coffee, exercise or a cold shower cannot speed it up.

   Source: Handbook p. 79

   “the liver can only oxidize about one drink per hour. Contrary to popular belief, this rate cannot be increased by drinking coffee, exercising, taking a cold shower or anything else. Only time can sober a person who’s been drinking.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 79

3. A 12 ounce beer has about the same alcohol as a 1 ounce shot of whiskey.

   Source: Handbook p. 83

   “The amount of alcohol in one (12 ounce) bottle of beer is about equal to that in a (1 ounce) shot of whiskey.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 83

4. At a BAC of 0.10 percent you are 7 times more likely to cause a crash.

   Source: Handbook p. 79

   “With a BAC of .10 percent, you are seven times more likely to cause a crash than if you were sober.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 79

5. At 0.17 percent BAC you are 50 times more likely to cause a crash.

   Source: Handbook p. 79

   “At .17 percent BAC, you are 50 times more likely to cause a crash.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 79

6. Side vision drops by about 30 percent at 0.05 percent BAC.

   Source: Handbook p. 80

   “Side vision is reduced by about 30 percent at .05 percent BAC.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 80

7. Reaction and coordination are impaired at a BAC as low as 0.02 percent.

   Source: Handbook p. 80

   “Reaction and coordination are impaired by alcohol consumption as low as .02 percent BAC.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 80

8. Alcohol is a depressant, not a stimulant.

   Source: Handbook p. 81

   “Alcohol, in any concentration, is a depressant, not a stimulant.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 81

9. A prescription is no defense for driving under the influence of a drug.

   Source: Handbook p. 81

   “Just because a drug is prescribed, by law, this is NO defense for driving under the influence of it.”
   Tennessee Comprehensive Driver License Manual, Handbook p. 81

10. DUI penalties are the same whether the driver used alcohol or drugs, even prescription or over the counter drugs.

    Source: Handbook p. 81

    “The penalties for a DUI arrest are the same whether the driver was drinking alcohol or taking drugs (even prescription or over-the-counter drugs).”
    Tennessee Comprehensive Driver License Manual, Handbook p. 81

Numbers to know

3 questions from the Tennessee practice test

1. 1. Which type of medication does Tennessee include in its warning about driving under the influence?

   1. Prescription drugs
   2. Only vitamins and mineral supplements
   3. Only medication taken in a hospital
   4. Prescription drugs are always safe for driving
   Show answer

   Prescription drugs. Tennessee's discussion of impaired driving expressly includes prescription drugs among substances that can affect a driver's ability. The warning is not limited to illegal substances, and a prescription does not guarantee that operating a vehicle is safe. The choices about vitamins, hospital-only medication, and automatic safety add limits that the passage does not state. Read the label and consider drowsiness, slowed reactions, or impaired judgment before starting the engine. If there is any doubt about the ability to drive, arrange another ride instead of testing the medication's effects on the road.

2. 2. What penalty applies when someone drives under the influence of drugs, including prescription drugs?

   1. A lesser penalty than for alcohol
   2. Only a warning for a first occurrence
   3. No penalty if the drug was prescribed
   4. The same penalties as for alcohol
   Show answer

   The same penalties as for alcohol. Tennessee treats driving under the influence of drugs, even prescription drugs, as carrying the same penalties as driving under the influence of alcohol. A prescription does not create a defense, and the absence of alcohol does not turn the conduct into a warning-only matter. The lesser-penalty choice reverses the manual’s comparison. When a medicine may affect alertness or control, read its warnings and do not drive if impairment is possible. The key study cue is equal DUI treatment for alcohol and drugs.

3. 3. Can Tennessee charge a driver who is impaired by an intoxicant even when the question is not limited to alcohol?

   1. Yes, driving under the influence of any intoxicant is unlawful
   2. No, only alcohol can support a charge
   3. Yes, but only on an interstate highway
   4. No, unless the driver is under 21
   Show answer

   Yes, driving under the influence of any intoxicant is unlawful. Tennessee's DUI rule covers driving or being in physical control while under the influence of an intoxicant, marijuana, narcotic drug, or drugs producing stimulating effects on the central nervous system. Alcohol is only one part of that rule. The interstate-only and under-21 limitations add restrictions that the manual does not impose. A driver should consider prescription and nonprescription substances as well as alcohol before driving. If a substance affects judgment, coordination, alertness, or other driving functions, choosing to drive can create both danger and criminal exposure.

Source: the Tennessee Comprehensive Driver License Manual, Section B-7: Alcohol, Other Drugs and Driving. This lesson is a plain English summary, not the law itself; where it differs, the manual and the statute govern. Last checked 2026-09-27.