Alcohol, Cannabis and Medications: How They Affect Your Driving

Most drivers know that drinking and driving is dangerous and illegal.

Fewer realize how broad the rules really are.

Impaired driving laws cover alcohol, cannabis, illegal drugs and many ordinary medications from the pharmacy.

A cold medicine or a new prescription can affect your driving as much as a drink.

This guide explains how impairment works, what the legal limits are and how to make a safe plan before you go out.

The legal details come from the California Driver Handbook.

Other states have similar rules, but check your own state driver handbook for the exact limits.

Impairment is about your ability, not the substance

The California Driver Handbook says the state's DUI laws apply to both alcohol and drugs.

It is illegal to drive under the influence of alcohol or any drug that affects your ability to drive safely.

The handbook makes an important point about medicine.

The law does not see a difference between illegal drugs and medications you get from a doctor or pharmacy.

They can all affect your ability to drive safely and react to what you see and hear.

According to the handbook, it is illegal at any age to drive after any of these:

  • Drinking excessive amounts of alcohol in any form, including medications like cough syrup.
  • Taking any drug that affects your ability to drive, including prescription or over-the-counter medications.
  • Using any combination of alcohol or drugs that decreases your ability to drive safely.

Medications: read the label every time

Many common medicines can make you drowsy, slow your reactions or blur your vision.

Allergy pills, sleep aids, muscle relaxers, strong pain relievers and some cold remedies are frequent examples.

The handbook says to read medication labels and know the effects of any drug you use.

Look for warnings such as may cause drowsiness or use care when operating a vehicle.

Pay special attention when you start a new medicine or change a dose.

That is when you know least about how it affects you.

If you are unsure, ask your pharmacist or doctor whether it is safe to drive.

Never stop or change a prescribed medicine on your own just to drive. Ask for advice first.

Mixing makes it worse

Combining substances multiplies the risk.

The National Institute on Alcohol Abuse and Alcoholism warns that drinking while taking some medications can be dangerous.

It names sleep aids, anti-anxiety medicines, opioid pain relievers and even over-the-counter antihistamines.

A small amount of alcohol on top of one of these can impair you far more than either one alone.

Blood alcohol limits

Blood alcohol concentration, or BAC, measures how much alcohol is in your bloodstream.

The California handbook lists these limits for driving:

  • 0.08% or higher if you are 21 or older.
  • 0.01% or higher if you are under 21.
  • 0.01% or higher at any age if you are on DUI probation.
  • 0.04% or higher if you drive a vehicle that requires a commercial license.
  • 0.04% or higher if you are driving a passenger for hire.

Under the limit does not mean safe

Many people treat the legal limit as a target. That is a mistake.

The handbook says almost everyone feels negative effects of alcohol, even below the legal limit.

It adds that even one drink can affect your ability to drive safely.

Depending on how impaired you are, you can be arrested and convicted of DUI without a BAC measurement.

The handbook also notes that tolerance to alcohol decreases as you age.

A drink that felt like nothing years ago may affect you more today.

Why coffee and cold air do not help

There is no quick way to sober up.

The NIAAA explains that BAC can keep rising even after a person stops drinking.

Alcohol still in the stomach and intestine continues to enter the bloodstream.

It also says that cold showers, hot coffee and walking do not reverse the effects of alcohol.

Coffee may make you feel more awake. It does not make you less impaired.

Only time lowers your BAC, and it takes longer than most people expect.

If you have been drinking, the safest choice is not to drive at all.

Alcohol and cannabis inside the car

The rules also cover what you carry in the vehicle.

The handbook says it is illegal to drink alcohol, or to smoke or eat a cannabis product, while driving.

That rule also applies to passengers in the vehicle.

Any alcohol or cannabis you carry must be in a sealed, unopened container.

If a container is open, keep it in the trunk or another place where passengers do not sit.

The glove box does not count. An open container of alcohol there is illegal.

The handbook notes an exception for passengers in a bus, taxi, camper or motorhome.

What happens after a DUI arrest

The consequences of impaired driving go far beyond a ticket.

The handbook explains that driving in California means you consent to a breath, blood or urine test if an officer suspects DUI.

Refusing a test leads the DMV to suspend or revoke your driving privilege.

After a DUI conviction, the handbook lists several requirements:

  • Completing a DUI program.
  • Filing proof of insurance with the state.
  • Paying license reissue or restriction fees.
  • Possibly installing an ignition interlock device on your vehicle.

Penalties can also include jail time, fines and having your vehicle impounded.

A DUI stays on your California driver record for 10 years.

If you cause serious injury or death, you may also face civil lawsuits.

Rules for drivers under 21

Young drivers face stricter rules in most states.

In California, drivers under 21 may not carry alcohol in a vehicle unless someone 21 or older is with them.

Even then, the container must be full, sealed and unopened, or kept in the trunk.

The handbook says a vehicle can be impounded for up to 30 days if alcohol is found.

The court may also fine the driver and suspend the license for one year.

How to plan a safe ride home

The best time to decide how you will get home is before the first drink.

  • Choose a designated driver who will not drink at all.
  • Plan to use a taxi, a rideshare or public transportation.
  • Arrange to stay over if you are at a friend's home.
  • Keep a little money or a ride app ready on your phone.
  • Eat before and while you drink, but do not count on food to keep you safe.

If a friend has been drinking, offer to call a ride or take the keys.

That conversation can feel awkward. It is far easier than the alternatives.

Fatigue adds to impairment

Alcohol and many medicines also make you sleepy.

Late nights out often mean driving at the hours when your body most wants to rest.

The combination makes slow reactions even slower.

Our guide to drowsy driving warning signs explains what to watch for.

A quick impaired driving checklist

  • Treat any drink as a reason not to drive.
  • Read every medication label for driving warnings.
  • Ask a pharmacist before driving on a new medicine.
  • Never mix alcohol with sleep, anxiety or pain medicines.
  • Keep any alcohol or cannabis sealed and out of the passenger area.
  • Plan your ride home before you go out.

The bottom line

Impaired driving is not only about alcohol, and it is not only about the legal limit.

Cannabis, illegal drugs and everyday medicines can all slow you down.

When in doubt, do not drive. Wait, call a ride or let someone else take the wheel.

Sources and Further Reading