Drugs, cannabis and medicines

By the end of this topic you can

• You can explain that driving impaired by any drug is illegal in every state.
• You can describe how cannabis and common medicines can affect driving.
• You can read a medicine label for warnings about driving or drowsiness.
• You can make a safe choice when you have taken something that may affect you.

What you need to know and understand

• Legal to use does not mean legal to drive: cannabis and prescription drugs can still lead to a DUI.
• Cannabis can slow reaction time, affect judgment of time and distance, and make it harder to stay in your lane.
• Many over-the-counter cold, allergy and sleep medicines cause drowsiness.
• Mixing alcohol with drugs, even a small amount of each, can make impairment much worse.
• Implied consent covers drug testing too: an officer may ask for a blood or urine test if drugs are suspected.
• How states test for drug impairment varies: some set specific THC limits, some have zero tolerance for certain drugs, and others rely on officer evidence. Check your state manual.
• In California, open container rules also apply to cannabis: it must be sealed or kept in the trunk.

Cannabis and driving

Cannabis affects people differently depending on the amount, the strength, how it is taken and the person. Edibles can take much longer to kick in and last longer than smoking, so people sometimes drive while still impaired without realizing it.

Even in states where adults may legally use cannabis, driving while impaired by it is a crime, and using it in a vehicle is banned. Combining cannabis with alcohol is especially dangerous. The safe rule is simple: if you have used cannabis, do not drive.

Checking your medicines

Do not stop taking a prescribed medicine on your own just so you can drive. Talk to your doctor: some conditions are more dangerous untreated.

1. Read the label and the leaflet for warnings such as 'may cause drowsiness' or 'use care when operating a vehicle'.
2. Ask your doctor or pharmacist whether it is safe to drive on a new medicine.
3. Try a new medicine at home first so you know how it affects you.
4. Never take more than the stated dose, and never mix with alcohol.
5. If you feel drowsy, dizzy or unfocused, do not drive. Arrange another ride.

Effects to watch for

• Depressants and sleep aids: drowsiness, slow reactions, poor coordination.
• Some allergy and cold medicines: drowsiness and blurred focus.
• Stimulants: overconfidence, risk-taking and a crash in alertness when they wear off.
• Opioid painkillers: drowsiness and slowed reactions.
• Combinations: effects can multiply and become unpredictable.

Common mistakes

• Thinking a doctor's prescription makes it legal to drive impaired: it does not.
• Driving soon after using an edible because you feel fine: effects may not have peaked.
• Ignoring drowsiness warnings on cold or allergy medicine: read every label.
• Having a drink while on medication: combinations can be far stronger.
• Keeping opened cannabis in the passenger area: store it sealed or in the trunk where required.

Test yourself: Drugs, cannabis and medicines

Answer each question, then read the explanation. Questions come in a random order each time.

Go deeper

• Drugged Driving and Cannabis