There are data showing that marijuana can play a role in motor vehicle crashes. Studies show that approximately 4-14 percent of drivers who sustained injury or died in traffic accidents tested positive for THC. In many of these cases, alcohol was detected as well.
There are some signs you might be able to see. If someone is high on marijuana, he or she might: seem dizzy and have trouble walking; seem silly and giggly for no reason; have very red, bloodshot eyes; and have a hard time remembering things that just happened. When the early effects fade, the user can become very sleepy.
There is no magic bullet for preventing teen drug use. But parents can be influential by talking to their children about the dangers of using marijuana and other drugs, and by remaining actively engaged in their children's lives.
Tolerance" means that the user needs increasingly larger doses of the drug to get the same desired results that he or she previously got from smaller amounts. Some frequent, heavy users of marijuana may develop tolerance for it.