Cannabis DUI in Montana: The Limits and Risks
Montana’s 5 ng/mL THC limit, why “feeling fine” isn’t a defense, and why a medical card doesn’t exempt you.
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Cannabis is legal for adults in Montana, but driving under its influence is not, and the rules are stricter than many people realize. (General information, not legal advice.)
Montana’s THC limit
Montana law makes it a DUI to drive with 5 ng/mL or more of THC (excluding inactive metabolites) in your blood, regardless of how you feel, similar to the 0.08 alcohol limit. You can also be charged at lower levels if you’re under the influence, based on driving behavior and other evidence.
Drivers under 21
For drivers under 21, any amount of THC (excluding inactive metabolites) in the blood counts as a DUI under Montana law.
A medical card doesn’t exempt you
Having a medical card doesn’t protect you from a cannabis DUI. Montana’s cannabis law doesn’t permit driving under the influence, and the same limits apply.
The practical reality
THC doesn’t clear the system the way alcohol does, so regular consumers can have detectable levels longer than occasional users. Feeling fine doesn’t guarantee you’re under the limit. Around here, where people drive real distances between Bigfork, Kalispell, Whitefish, and the lake, the risk is genuine. The simple rule: if you’ve consumed, don’t drive.
Sources checked Nov 6, 2026: MCA 61-8-1002; MCA 16-12-108. General information only; not legal or medical advice.
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