Drugged Driving (DUID): Marijuana, Prescriptions, and Other Drugs
How impaired-by-drugs charges work, why a valid prescription or legal cannabis is not a free pass, and how states differ.
Quick Answer
Driving while impaired by drugs is against the law in every state, whether the drug is illegal, a prescription, or bought over the counter. Cannabis being legal in a state does not make impaired driving legal. How states prove it differs: some require proof of impairment, and some also set per se limits or ban driving with any amount of certain drugs in your system.
Educational information, not legal advice. This is a general national overview. DUI and DWI laws are set by each state and change often, so details differ where you are. Use the state guides linked below and speak with a licensed attorney in the state where you were stopped or charged.
What counts as drugged driving
NHTSA describes drug-impaired driving as driving after taking illegal drugs, prescription medications, or over-the-counter medicines that affect your ability to drive safely. States use different names, including DUID (driving under the influence of drugs), DWI, OWI, or the same DUI statute that covers alcohol, which often prohibits impairment by alcohol, drugs, or a combination.
A valid prescription is generally not a defense to a charge of driving while impaired. What matters is whether the substance impaired your ability to drive, or in some states whether it is present at all.
Sources: NHTSA: Drug-impaired driving
Marijuana
Many states have legalized cannabis for medical or adult use, but driving while impaired by it remains an offense. NHTSA's report to Congress on marijuana-impaired driving reviewed the research and described the difficulty of tying a specific THC level in blood to a specific degree of impairment, which is one reason states have taken different approaches.
Some states require the prosecution to prove actual impairment. Others have per se laws that make it an offense to drive with a set amount of THC in the blood, and a few prohibit driving with any detectable amount of certain drugs. Which approach applies depends on the state.
Where laws vary: whether a state uses an impairment standard, a per se limit, or a zero-tolerance rule for drugs, and how it treats medical marijuana patients, is set by state statute. Check your state guide and the statute it links.
Sources: NHTSA: Marijuana-Impaired Driving, a Report to Congress (DOT HS 812 440) · NHTSA: Drug-impaired driving
Prescription and over-the-counter drugs
Medications such as some sleep aids, pain medicines, anti-anxiety drugs, and even some cold and allergy products can cause drowsiness or slow reaction time. NHTSA lists prescription and over-the-counter medicines among the drugs that can impair driving and recommends reading labels and talking to a doctor or pharmacist about driving.
Taking a drug exactly as prescribed does not necessarily protect you if it impairs your driving. Taking it as a combination with alcohol can also lead to a charge, and the same DUI statutes usually cover combined impairment.
Sources: NHTSA: Dangers of driving after taking prescription drugs or over-the-counter medicines · NHTSA: Drug-impaired driving
How drug impairment is investigated
- An officer observes driving and roadside behavior and may use field sobriety tests; see our guide on those tests.
- A specially trained Drug Recognition Expert (DRE) may perform a structured evaluation. NHTSA and the International Association of Chiefs of Police run the Drug Evaluation and Classification program that trains DREs.
- A blood or urine test may be requested, and officers often seek a warrant. Birchfield limits warrantless blood draws and the penalties a state may impose for refusing them.
- Unlike a breath test for alcohol, there is no single roadside device for drug impairment that every state accepts, although some states are using oral-fluid screening devices. These cases often rely on the officer's observations and later lab results. Ask what your state uses.
Sources: NHTSA: Drug Evaluation and Classification program · Birchfield v. North Dakota (U.S. Supreme Court, 2016)
Consequences
A drugged driving conviction can carry penalties comparable to an alcohol DUI, including a license suspension, fines, and possibly jail. A refusal of a required chemical test can carry its own administrative penalties under implied consent. Drug charges can also be filed separately from the driving charge, for example for possession.
Commercial drivers and those with professional licenses can face additional consequences. See the career guides for those situations.
Sources: NHTSA: Drug-impaired driving