Ambien, Sleep-Driving, and DUI in Montana

Sleep medication leads to DUI charges in two very different ways. In one, a person is awake and driving while the drug is still working, often the next morning. In the other, a person takes the medication, goes to bed, and is later found behind the wheel with no memory of getting there. Montana law treats the first as an ordinary impairment case. The second raises a real question about whether the person acted voluntarily. This page explains both. It is part of our Montana DUI Guide.

Sleep Medication Under Montana's DUI Statute

Montana's impairment offense covers alcohol, "any drug," or a combination (MCA § 61-8-1002(1)(a)). A drug is any substance that when taken into the body can impair a person's ability to operate a vehicle safely (MCA § 61-8-1001(7)). Prescription sleep aids fit that definition, and so do over-the-counter sleep products.

Zolpidem, eszopiclone, and zaleplon do not appear on the per se drug list, so no blood level is an offense in itself. The State has to prove impairment, and the evidence statute says a positive test "does not, in itself, prove that the person was under the influence" (MCA § 61-8-1018(1)(a)). There must be other competent evidence, such as the driving, the officer's observations, and roadside tests.

What the FDA and NHTSA Say About These Drugs

Two federal warnings shape these cases.

Next-morning impairment.In 2013 the FDA required lower recommended doses for zolpidem products. Its announcement stated that patients who take insomnia drugs can experience impaired mental alertness the morning after use, that this can happen even when a person feels fully awake, and that the risk is highest with extended-release forms. The FDA also advised against taking a bedtime insomnia medicine when less than a full night's sleep (7 to 8 hours) remains.

Complex sleep behaviors. On April 30, 2019, the FDA announced a boxed warning for eszopiclone (Lunesta), zaleplon (Sonata), and zolpidem (Ambien, Ambien CR, Edluar, Intermezzo, Zolpimist). It covers sleepwalking, sleep-driving, and other activities carried out while not fully awake, and says these behaviors have resulted in serious injuries and deaths. The FDA told prescribers not to give these drugs to patients who have previously had such an episode.

NHTSA's Drugs and Human Performance Fact Sheets: 2024 classify zolpidem as a central nervous system depressant. The case reports they summarize describe erratic driving, slow and slurred speech, confusion, disorientation, and poor performance on field sobriety tests. To an officer, that picture can look like alcohol.

Four Common Fact Patterns

The table is a general map, not a prediction. Which row a case belongs in is often the disputed question.

Sleep-Driving and the Voluntary Act Rule

DUI is an absolute liability offense (MCA § 61-8-1002(5)), so the State never has to prove you intended to drive impaired. But Montana's criminal code makes a voluntary act a material element of every offense (MCA § 45-2-202), and it defines an involuntary act to include "a bodily movement during unconsciousness or sleep" (MCA § 45-2-101).

In City of Missoula v. Paffhausen, 2012 MT 265, the Montana Supreme Court held that a DUI defendant could raise automatism as an affirmative defense, because the voluntary act requirement applies even to absolute liability offenses. The Court noted its earlier statement that the defense may apply where a person "acts during convulsions, sleep, unconsciousness, hypnosis or seizures" (¶ 24, quoting State v. Korell).

That is the legal foundation for a sleep-driving defense. Its limits matter just as much:

• Paffhausen involved a claim that a third party drugged the driver. It did not decide a case in which the person knowingly took a prescribed sleep aid.
• The State can be expected to argue that taking the medication was itself a voluntary act, particularly if the person ignored label directions, mixed it with alcohol, or had a previous episode.
• The defendant must give written notice of the defense at or before the omnibus hearing and present admissible evidence, usually medical or pharmacological, at a pretrial hearing (Paffhausen, ¶¶ 37 to 38).

Our page on involuntary intoxication explains the Paffhausen procedure in detail.

Evidence That Matters in a Sleep Medication Case

• The prescription record: the drug, the dose, how long you have taken it, and what the label and pharmacy handout said.
• The timeline: when you took it, when you went to bed, and when you were found driving.
• Memory and behavior: what you recall, what you were wearing, where you were going, and what the officer's video shows.
• Other substances: any alcohol or other sedating medication. NHTSA reports that alcohol produced additive effects with a 10 mg dose of zolpidem in one controlled study.
• History: whether you have had sleepwalking or similar episodes before, and whether you told your prescriber.
• The blood test: what the laboratory looked for and how the sample was drawn and handled.

Sleeping in the Car After Taking a Sleep Aid

Some people take a sleep aid and then rest in a parked vehicle. Montana's DUI law reaches a person in actual physical controlof a vehicle, not only a person who is driving, so being asleep in the driver's seat does not by itself rule out a charge.

If You Are Charged

Do not stop a prescribed medication on your own because of a charge; talk to your prescriber. Do tell your lawyer about every medication and when you took it, and gather the pharmacy records early. The broader rules for medication cases are in our guide to prescription and drug DUI.

This page explains Montana law in general as of the 2025 Montana Code Annotated. It is not legal or medical advice. Do not stop or change a prescribed medication without talking to your prescriber.