The Short Answer

Driving while impaired by cannabis is illegal in all 50 states, including states where recreational marijuana is legal. A medical marijuana card does not protect you from a DUI charge. Most states do not need a specific THC number to convict. They combine an officer's notes, field sobriety tests, and a blood or urine test. Some states go further with a per se THC limit or a zero tolerance rule.

Cannabis Impaired Driving Laws: A Guide for US Drivers

How States Define THC Impairment

Zero tolerance

In these states, any detectable amount of THC or its metabolites in the blood supports a charge. You do not have to look or act impaired. Metabolites can stay in the body for days or weeks after last use, so a test can show a positive result long after the high has passed.

cannabis driving laws in us

Per se limits

A small number of states set a number, most often 5 nanograms of THC per milliliter of blood. At or above that number, the law assumes impairment. Below it, an officer can still charge you based on observed behavior.

cannabis driving laws in us

Impairment based

These states have no set number. The prosecution must show that your driving was affected. Officer testimony, dash camera video, and field sobriety test results carry the case.

legal implications of cannabis and driving

Where CBD Fits

Federal law allows hemp CBD with no more than 0.3 percent THC. Full spectrum products can still contain trace THC, and daily use can push a person past a zero tolerance threshold. CBD itself is not known to impair driving, but a positive THC test is what starts the case. If you use CBD and you drive, choose isolate or broad spectrum products and read the certificate of analysis for the THC result.

If You Get Pulled Over

  1. Signal and pull over at the first safe spot.
  2. Stay in the car, keep your hands on the wheel, and turn on the interior light at night.
  3. Hand over your license, registration, and insurance when asked.
  4. Answer questions about your identity, then decline to discuss what you used or when.
  5. You can refuse roadside field sobriety tests in most states. Those tests are voluntary in many places, but a refusal can be used as evidence.
  6. Understand implied consent before you refuse a blood or urine test. A refusal often triggers an automatic license suspension, and the officer may seek a warrant.
  7. Ask for a lawyer before you sign anything or answer questions about your cannabis use.

Penalties You Can Expect

  • First offense fines that range from a few hundred to several thousand dollars
  • License suspension from 90 days to a year
  • Possible jail time, especially with a high THC reading or a crash
  • Ignition interlock or drug education classes in some states
  • Higher insurance rates for years
  • A commercial driver's license suspension, since federal rules bar any marijuana use for CDL holders

Reduce Your Risk

  1. Set a rule that you do not drive on any day you use THC.
  2. Store any cannabis product in a sealed container in the trunk, not in the cabin.
  3. Do not use cannabis in a parked car. Open container and consumption laws still apply.
  4. Keep your medical card or purchase receipt with you if your state asks for proof.
  5. Check the law in each state you plan to cross. A legal product at home may not be legal at your destination.
  6. Skip alcohol and sedating medication when you use cannabis. The mix raises impairment.