The 2025 Montana Legislature changed DUI law in several ways, all effective October 1, 2025: a new offense based on blood levels of specific drugs, a zero-THC rule for drivers under 21, oral fluid testing for alcohol, a broader definition of a prior conviction, and a new homicide offense. This page lists each change with the bill and the current statute. It is part of our Montana DUI Guide.
The Bills at a Glance
| Bill (2025 session law) | What it did | Current MCA |
|---|---|---|
| HB 344 (Ch. 264) | Created a new DUI offense for having a listed drug at or above a set blood level without a valid prescription. | § 61-8-1002(1)(f) |
| SB 508 (Ch. 412) | Made any amount of active THC a DUI for a driver under 21. | § 61-8-1002(1)(e)(ii) |
| HB 467 (Ch. 298) | Added oral fluid as a sample for alcohol testing and for showing alcohol concentration. | §§ 61-8-1002(1), 61-8-1016(1)(a) |
| HB 626 (Ch. 702) | Lets a pending or later offense count as a prior if it becomes a conviction before sentencing. | § 61-8-1011(1)(a)(iii) |
| HB 267 (Ch. 226) | Created aggravated vehicular homicide while under the influence. | § 45-5-107 |
| HB 712 (Ch. 509) | Requires restitution for a victim's surviving minor child after vehicular homicide while under the influence. | § 45-5-106(4) |
| SB 380 (Ch. 395) | A broad motor vehicle bill that also edited the test refusal sections. | §§ 61-8-1016, 61-8-1017, 61-8-1032 |
We traced these from the history lines of each section in Title 61, chapter 8, part 10 and from the enrolled bills. Two code-cleanup bills (HB 99 and HB 112) also touched the part. A change made somewhere else in the code that affects DUI cases indirectly may not appear here.
1. Blood Limits for Specific Drugs
Before 2025, Montana had numeric limits only for alcohol and THC. Any other drug case had to be proved as impairment. HB 344 added MCA § 61-8-1002(1)(f): a person commits DUI by driving or being in actual physical control of a vehicle on the ways of this state open to the public "while, without a valid prescription," the person has one of these substances in the blood at or above the listed amount.
| Substance | Blood level (ng/mL) |
|---|---|
| Amphetamine | 20 |
| Cocaine | 20 |
| Cocaine metabolite | 20 |
| Heroin | 1 |
| Morphine (as a heroin metabolite) | 20 |
| 6-monoacetyl morphine (a heroin metabolite) | 1 |
| Lysergic acid diethylamide (LSD) | 0.1 |
| Methamphetamine | 20 |
| Phencyclidine (PCP) | 5 |
| Fentanyl | 0.5 |
Three points. The offense requires a blood analysis. It applies only "without a valid prescription," so a patient lawfully prescribed one of these drugs is outside (1)(f), though still subject to the impairment offense. And a conviction is sentenced on the same schedule as a 0.08 offense and can be the basis for an aggravated DUI (MCA §§ 61-8-1007(2), 61-8-1001(1)). See Montana's drug per se limits.
2. Any THC for Drivers Under 21
SB 508 added a second way to commit the under-21 offense. It was already a violation for a driver under 21 to have an alcohol concentration of 0.02 or more. Now it is also a violation to drive with "any amount of tetrahydrocannabinol, excluding inactive metabolites," in the body, as shown by analysis of blood or another bodily substance (MCA § 61-8-1002(1)(e)(ii)). Adults remain subject to the 5 ng/mL limit in (1)(d). See under-21 DUI and THC DUI.
3. Oral Fluid Testing for Alcohol
Oral fluid was already in the implied consent statute for drug testing. HB 467 extended it to alcohol. The consent provision now covers "a test or tests of the person's blood, breath, or oral fluid" for alcohol (MCA § 61-8-1016(1)(a)), and the alcohol offenses now refer to analysis of "blood, breath, oral fluid, or other bodily substance" (MCA § 61-8-1002(1)(b), (c)). The same bill made a matching change for commercial drivers.
The definition of alcohol concentration was not changed. It still speaks only of grams per 100 milliliters of blood or per 210 liters of breath (MCA § 61-8-1001(3)), which leaves a real question about how an oral fluid result is expressed as an alcohol concentration. We are not aware of a court decision on it.
4. Pending Charges Can Become Priors
HB 626 changed the definition of a conviction used to count prior offenses. It now includes "a pending or subsequent offense if the pending or subsequent offense results in a conviction prior to sentencing for the present offense" (MCA § 61-8-1011(1)(a)(iii)).
In plain terms, the order of arrests no longer controls. If a person has two open DUI cases and one becomes a conviction first, the other can be sentenced as a second offense, with the higher minimums that brings. See a second DUI while the first is pending.
5. A New Homicide Offense, and Child Restitution
HB 267 created aggravated vehicular homicide while under the influence (MCA § 45-5-107). It applies when a person causes a death while violating § 61-8-1002(1)(a), (b), (c), or (d) and the facts also meet the definition of aggravated DUI, such as an alcohol concentration of 0.16 or more. The penalty is 3 to 30 years in prison, a fine of $10,000 to $50,000, or both. Sentence may not be deferred, and the first 3 years may not be suspended except under the exceptions in § 46-18-222. A person with a prior conviction under this section, like one under § 45-5-106, is punished for any later DUI under the felony statute, § 61-8-1008 (MCA § 61-8-1007(1)(b)).
HB 712 amended the existing vehicular homicide statute so that, if the victim has a surviving minor child, the convicted person "must be ordered to pay restitution" for the child's support (MCA § 45-5-106(4)). See DUI with a crash or a child in the car.
6. Refusal Statute Edits, and What Stayed the Same
SB 380 was a long motor vehicle bill, and three of its sections amended the refusal statutes. Comparing the enrolled bill with the current code, the edits removed language about an officer seizing the physical license. The parts most people ask about read the same as before: a 6-month suspension for a first refusal and 1 year for a second within 5 years, no probationary license, a $300 administrative fee, and 30 days to petition the district court (MCA §§ 61-8-1032, 61-8-1017). See test refusal in Montana.
Several other things people ask about were left alone:
- The 0.08, 0.04 (commercial), and 0.02 (under 21) alcohol limits.
- The 5 ng/mL THC limit for adults.
- The jail and fine ranges for first through third offenses in MCA § 61-8-1007.
- The rule that a DUI sentence cannot be deferred (MCA § 61-8-1011(4)).
For how today's section numbers relate to the ones used before 2022, see old and new DUI statute numbers.
This page summarizes 2025 Montana session laws as reflected in the 2025 Montana Code Annotated. New statutes have little case law, and how courts will apply them is not settled. It is not legal advice about your specific case.