There are data showing that marijuana can play a role in crashes. When users combine marijuana with alcohol, as they often do, the hazards of driving can be more severe than with either drug alone.
A study of patients in a shock-trauma unit who had been in traffic accidents revealed that 15 percent of those who had been driving a car or motorcycle had been smoking marijuana, and another 17 percent had both THC and alcohol in their blood.
In one study conducted in Memphis, TN, researchers found that, of 150 reckless drivers who were tested for drugs at the arrest scene, 33 percent tested positive for marijuana, and 12 percent tested positive for both marijuana and cocaine. Data also show that while smoking marijuana, people show the same lack of coordination on standard "drunk driver" tests as do people who have had too much to drink.
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