Marijuana and substance use — Missouri Permit Test

Marijuana and substance use on the Missouri permit test — 6 rules, each with the reason behind it and a question on it while it is fresh.

The rules

Marijuana is the second most cited drug in car crashes, after alcohol.

Second on a list nobody wants to be on, and the gap between first and second is not as wide as people assume.

Marijuana is the second most cited drug in car crashes, after alcohol.

Missouri Driver Guide, p.72

Even though medical marijuana was approved by Missouri voters, it is never legal or safe to drive while under the influence of marijuana.

Legal to possess and legal to drive on are different questions, and the guide answers the second one plainly.

it is never legal or safe to drive while under the influence of marijuana

Missouri Driver Guide, p.72

Marijuana can impair cognitive function, impair judgment of time and distance, and decrease coordination.

Judging time and distance is what a driver does at every intersection.

Marijuana can impair cognitive function, impair judgment of time and distance, and decrease coordination.

Missouri Driver Guide, p.72

Research shows marijuana increases lane weaving, slows reaction time, and alters attention to the road, and using alcohol with it makes drivers even more impaired.

The combination is worse than either alone, which is the finding the guide singles out.

Use of alcohol with marijuana made drivers even more impaired, causing even more lane weaving.

Missouri Driver Guide, p.72

One of the greatest predictors of developing an addiction is early use, because a young person's under-developed brain can be damaged faster and more severely than an adult's.

The same substance does more harm to a brain that has not finished growing.

A young person’s under-developed brain can become damaged quicker and more severely than an adult brain using the same substances.

Missouri Driver Guide, p.72

A substance use disorder occurs when recurrent use of alcohol or drugs causes significant impairment, such as health problems, disability, or failure to meet responsibilities at work, school, or home.

It is defined by what it costs a person's life rather than by how much they use.

Substance use disorders occur when the recurrent use of alcohol and/or drugs causes clinically and functionally significant impairment

Missouri Driver Guide, p.72

On the test

Where does marijuana rank among drugs cited in car crashes?

Second, after alcohol. Second on a list nobody wants to be on, and the gap between first and second is not as wide as people assume. Missouri Driver Guide, p.72: “Marijuana is the second most cited drug in car crashes, after alcohol.”

How this works

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Where these come from

Every rule here is checked against Missouri Driver Guide, published by the Missouri Department of Revenue, and against the state code itself. Last checked 2026-09-16.