What You Need to Know about Substance Use and Driving – Including Marijuana

"Each December, we recognize National Impaired Driving Prevention Month to raise awareness about the dangers of impaired driving and how to prevent impaired driving and related crashes, injuries, and deaths.

Driving while impaired by any substance is dangerous and illegal. The following substances can impair driving:

• Alcohol
• Marijuana
• Other illicit drugs like heroin, cocaine, methamphetamine, or hallucinogens
• Some prescription medications like opioids and antidepressants
• Some over-the-counter medications like sleep aids and allergy medicines

Fast Facts

• 11,654 people in the United States were killed in alcohol-impaired driving crashes in 2020—a 14% increase from 2019. That’s about 32 people every day or one person every 45 minutes.^[i]
• 7 million Americans reported driving under the influence of marijuana or other illicit drugs in 2020.^[ii]
• Alcohol and marijuana were the two most commonly reported substances involved in impaired driving in 2018, with 8% and 4.7% of the U.S. population aged ≥16 years reporting alcohol and marijuana respectively.^[iii]
• 1 in 8 high school student drivers reported driving after using marijuana at least once during the past month in 2017.^[iv]

How Does Substance Use Affect Driving?

How Marijuana Use Affects Driving

Driving is a complex task that requires your full attention to stay safe and alert. Marijuana use affects areas of the brain that control your body’s movements, balance, coordination, memory, and judgment. Marijuana use can impair important skills required for safe driving by:

• Slowing your reaction time and ability to make decisions
• Making it difficult to multitask
• Impairing coordination
• Distorting perception^{[i],[ii],[iii]}

If you are impaired, you cannot drive safely. It is illegal and dangerous to drive if you are impaired after using marijuana.

How Alcohol Affects Driving

The amount of alcohol in a person’s system is called blood alcohol concentration (BAC). Most states have set the legal BAC limit for driving at 0.08 grams of alcohol per deciliter (g/dL); the limit is 0.05g/dL in Utah.^[i] However, impairment starts at lower BAC levels, with even small amounts of alcohol affecting the ability to drive. The effects of alcohol use on driving include:

• Difficulty steering
• Reduced ability to respond to emergency driving situations
• Reduced ability to maintain lane position and brake appropriately
• Reduced ability to process what is happening on the road.."
  Impaired driving