Last verified: March 2026

How Maine's Cannabis DUI Law Works

Maine's cannabis DUI (called OUI — Operating Under the Influence) is governed by 29-A M.R.S. §2411. Unlike many legal states, Maine has no per se THC blood level for cannabis impairment. The legislature specifically rejected a proposed 5 ng/mL threshold, opting instead for a purely impairment-based standard.

This means prosecutors must prove that a driver was actually impaired by cannabis — not merely that THC was present in their system. This is a more scientifically sound approach, since THC can remain detectable in blood for days or weeks after use, long after any impairment has passed.

A person commits OUI if that person operates a motor vehicle while under the influence of intoxicants, meaning that person's mental or physical faculties are impaired however slightly or to any extent by the intoxicant.

29-A M.R.S. §2411 — Operating Under the Influence

No Per Se THC Limit: What This Means

Many states set a specific THC blood concentration (typically 5 ng/mL) above which a driver is automatically presumed impaired, regardless of actual driving behavior. Maine rejected this approach. Instead:

How Impairment Is Determined

Since there is no chemical threshold, Maine relies on observational evidence to establish cannabis impairment:

Standardized Field Sobriety Tests (SFSTs)

• Horizontal gaze nystagmus (eye tracking)
• Walk-and-turn test
• One-leg stand test

Drug Recognition Expert (DRE) Evaluations

Maine employs certified Drug Recognition Experts (DREs) — officers with specialized training in identifying drug impairment. A DRE evaluation includes:

• A 12-step protocol assessing vital signs, pupil size, muscle tone, and coordination
• Interview and behavioral observations
• Assessment of which drug category (if any) is consistent with the observed signs

DRE testimony is often a key piece of evidence in cannabis OUI cases.

The "However Slightly" Standard

While the impairment-based approach is fairer than a per se limit, the legal threshold is low. Maine law states that impairment "however slightly or to any extent" is sufficient. This means even mild effects from cannabis can technically constitute OUI. Prosecutors do not need to prove severe impairment — any degree of impairment is enough.

OUI Penalty Escalation

First Offense

Second and Third Offenses

Penalties escalate significantly with each subsequent OUI conviction, including longer mandatory jail time, higher fines, and extended license suspensions.

Fourth Offense: Felony

For the complete penalty breakdown, see Penalties.

Open Container Rules

Having an open cannabis container accessible in a vehicle is a civil violation. Best practices for transporting cannabis:

• Keep cannabis in its original sealed dispensary packaging
• Store it in the trunk or a locked compartment, not the glove box or center console
• Never consume in a parked vehicle — it is still considered "operating" in many circumstances

Practical Tips

• Do not drive after consuming. Wait at least 4 hours after smoking/vaping and 6–8 hours after edibles
• Maine's impairment standard protects sober regular users from the per se trap that exists in states like Colorado and Washington, where residual THC can trigger automatic DUI
• But "however slightly" is a low bar. If you feel any effects at all, do not drive
• Use rideshare or a designated driver. Uber and Lyft are available in Portland, Bangor, and other populated areas
• Store cannabis properly in your vehicle. A sealed container in the trunk avoids open container issues

For more on how cannabis affects driving ability, see Driving & Impairment on TryCannabis.org.

Official Sources

• Office of Cannabis Policy (OCP)
• 29-A M.R.S. §2411 — Operating Under the Influence