Which of the following can impair driving but is not an alcohol?

Marijuana is known to have several psychoactive effects that can impair cognitive functions and motor skills, which significantly impact the ability to drive safely. It can alter perception, reaction times, and overall coordination, making it dangerous to operate a vehicle under its influence. The effects of marijuana can linger well beyond the initial high, affecting a driver's ability to focus on the road, make quick decisions, and react to unexpected situations.

Other options, like alcohol, are alcohol and obviously impair driving capabilities. Caffeine, while it may affect alertness, typically does not impair driving in the same way that marijuana does. Nicotine may cause temporary increases in alertness, but it is not considered to impair driving in the way that psychoactive substances like marijuana do. Therefore, the identification of marijuana as a substance that can impair driving but is not classified as alcohol is accurate and critical for understanding the broader spectrum of substances that affect driving safety.