Operating Under the Influence of Drugs in Massachusetts: No THC Limit, Roadside Assessments, and Your Defenses

Operating under the influence is not only about alcohol. Massachusetts law makes it the same crime, with the same penalties, to drive while impaired by marijuana, narcotics, depressants, stimulants, or inhaled toxic fumes. But drug cases are proved very differently. There is no legal limit for THC, no breath test for drugs, and strict limits on what a police officer can say about whether you were “high.” Those differences are where many drug OUI defenses are built.

What the Law Covers

G.L. c. 90, § 24(1)(a)(1) punishes operating a motor vehicle on a public way, or in a place where the public has a right of access, “while under the influence of intoxicating liquor, or of marijuana, narcotic drugs, depressants or stimulant substances, all as defined in section one of chapter ninety-four C, or while under the influence from smelling or inhaling the fumes of any substance having the property of releasing toxic vapors.”

The toxic-vapors language took effect April 13, 2018 (St. 2018, c. 69, § 32). It replaced the old phrase “vapors of glue” and reaches fumes intentionally smelled or inhaled to get high, as defined in G.L. c. 270, § 18.

What the Commonwealth Must Prove

Under the District Court model jury instruction for OUI-drugs (Instruction 5.400, revised July 2024), the Commonwealth must prove three things beyond a reasonable doubt:

• You operated a motor vehicle.
• You did so on a public way, in a place where the public has a right of access, or in a place where the public has access as invitees or licensees.
• While operating, you were under the influence of marijuana, a narcotic drug, a depressant, a stimulant substance, or toxic fumes.

“Under the influence” means you had consumed enough of the substance to reduce your ability to drive safely by diminishing your alertness, judgment, and ability to respond promptly. The Commonwealth does not have to prove you actually drove badly, but it must prove a diminished capacity to drive safely.

The drug has to fit a listed category

It is not enough to prove you took “a drug.” The substance must be marijuana or fall within the definitions of narcotic drug, depressant, or stimulant substance in G.L. c. 94C, § 1. That can matter. The statutory definition of “narcotic drug” covers opium, opiates, and coca leaves and their derivatives, but does not name heroin, codeine, or cocaine. The Commonwealth must prove the link by expert testimony or ask the judge to take judicial notice of it; if it does neither, the defendant must be acquitted (Commonwealth v. Green, 408 Mass. 48 (1990), codeine). Some other depressants and stimulants require proof that the substance has been designated under federal regulations.

Marijuana: No Legal Limit and No Breath Test

For alcohol, the statute sets a per se limit: a blood alcohol level of .08 or more is a crime by itself. There is no equivalent for marijuana or any other drug. The statute sets no THC level, so the Commonwealth must prove actual impairment every time.

There is also no breath test for drugs. The Supreme Judicial Court has noted that marijuana, unlike alcohol, does not act as a general depressant across the body, and that its effects “vary greatly amongst individuals” (Commonwealth v. Gerhardt, 477 Mass. 775 (2017)). A test showing THC in your system is not the same as proof that you were impaired while driving.

Field Sobriety Tests in a Drug Case

In Gerhardt, the SJC found no scientific consensus that standard field sobriety tests measure marijuana impairment. It set firm rules for marijuana cases:

• The tests may be described only as “roadside assessments,” not field sobriety tests.
• The officer may describe what you did, as evidence of balance, coordination, mental clarity, following directions, and dividing attention.
• The officer may not say you “passed” or “failed,” or that your performance showed you were under the influence.
• The jury is told the assessments are not scientific tests of drug impairment, that a person can struggle with them for reasons unrelated to drugs, and that performance on them, standing alone, is never enough to convict.

The current model instruction applies the same roadside-assessment rules to every OUI-drugs charge, not only marijuana, and calls for the term “roadside assessments” when alcohol and drug charges are tried together.

What a Police Officer Can and Cannot Say

In an alcohol case, a police officer or other lay witness may give an opinion that a driver appeared intoxicated. In a marijuana case, Gerhardt holds that neither a police officer nor any other lay witness may offer an opinion that the driver was “high” or under the influence of marijuana. The officer may testify to observable facts such as bloodshot eyes, drowsiness, and lack of coordination, but may not say what those signs mean. Jurors may then use their own common sense about the effects of marijuana.

Drug Recognition Experts

Some police officers are trained as drug recognition experts (DREs), who run a structured evaluation and assign a suspected drug category. Training alone does not make that conclusion admissible. Under Gerhardt, only a witness qualified as an expert may offer an opinion that a driver was impaired by marijuana, and expert testimony must meet the Massachusetts reliability standard (Mass. G. Evid. § 702; Commonwealth v. Lanigan, 419 Mass. 15 (1994)). The SJC has not ruled that DRE opinions meet that standard, and the defense can ask the court for a hearing to test their reliability before trial. See Do I Need an Expert Witness?

Lab Results and Drug Evidence

A certificate of drug analysis is admissible only with live testimony from the analyst who did the work (Melendez-Diaz v. Massachusetts, 557 U.S. 305 (2009)). Proof of what a substance was, and that it impaired the driver, can also come from circumstantial evidence, but a witness’s statement that something “looked like” a drug will rarely be enough on its own.

Prescription Drugs

A valid prescription is not a defense by itself. But the statute punishes only voluntary intoxication by drugs whose effects you knew or should have known. If the evidence suggests a prescribed medication caused the impairment, the Commonwealth must prove beyond a reasonable doubt that you either received warnings about the medication or had reason to anticipate its intoxicating effects. If it cannot, you must be found not guilty (Commonwealth v. Wallace, 14 Mass. App. Ct. 358 (1982)). The jury may consider whether a reasonable person would have asked a doctor about the effects, and the judge may take notice that pharmacists must label prescriptions with required warnings (G.L. c. 94C, § 21).

If a drug was one cause of the impairment, it is no defense that something else, such as alcohol, made it worse.

Penalties

OUI-drugs is charged under the same statute as alcohol OUI and carries the same penalties. A first offense is punishable by a fine of $500 to $5,000, up to 2½ years in the house of correction, or both. Repeat offenses carry mandatory jail and higher fines, and a third offense is a felony. See our OUI guide for penalties by offense number.

License Consequences

• Conviction: the same license losses as alcohol OUI apply, starting at 1 year for a first conviction (G.L. c. 90, § 24(1)(c)).
• 24D disposition: the first-offender program is available for controlled-substance OUI. It carries a 45 to 90 day license loss and a chance to apply for a hardship license (G.L. c. 90, § 24D).

Defenses

• No proof of impairment: without a legal limit, the case rests on observations. Fatigue, nerves, medical conditions, and the conditions of the stop can explain them.
• Roadside assessments: they are not scientific tests of drug impairment and can never convict on their own.
• Improper opinion testimony: the officer cannot say you were high, and a DRE’s opinion must pass a reliability challenge.
• The substance: the Commonwealth must prove the drug falls within a listed category, with proper lab testimony.
• Prescription medication: if you had no warning and no reason to expect the effect, the intoxication was not voluntary.
• Operation and public way: the same elements as any OUI must still be proved.

Why a Lawyer Matters

Drug OUI cases turn on evidence rules that do not apply the same way in alcohol cases: what an officer may say, whether an expert is reliable, and whether the substance is proved. A lawyer who knows those rules can keep improper evidence out and hold the Commonwealth to its proof. Attorney William J. Barabino has defended OUI cases for 23 years. Call 781-393-5900.

Related Charges

• OUI-alcohol (G.L. c. 90, § 24): the same statute, with alcohol and a .08 per se limit.
• OUI child endangerment (G.L. c. 90, § 24V): an added charge when a child 14 or younger is in the vehicle.
• Negligent operation (G.L. c. 90, § 24(2)(a)): driving so as to endanger, with no proof of impairment required.
• Drug possession (G.L. c. 94C, § 34): a separate charge when drugs are found in the car.
• Motor vehicle homicide (G.L. c. 90, § 24G): impaired or negligent operation that causes a death.

Disclaimer

This article is for general educational information about Massachusetts criminal law. It is not legal advice for your situation, and reading it does not create an attorney-client relationship. Laws change. For advice about a specific case, speak with a licensed Massachusetts attorney.