Even on drink affects your nervous system, and impairs your judgement and motor skills. A teen can become addicted to alcohol quicker tha an adult because the body doesn't fully mature until aroub 21 years of age. Young smokers are more likely to use other drugs. Smoking alos hurts your performance in any sports activity. The most harmful effect is the strong likelihood of a lifelong addiction leading to many serious diseases.
All tobacco contains nicotine-which is very addictive.
Good reflexes and sound judgement are critical when driving, but drugs impare both.