For some people, marijuana raises blood pressure slightly and can double the normal heart rate. This effect can be greater when other drugs are mixed with marijuana, but users do not always know when that happens. As the immediate effects fade, usually after 2 to 3 hours, the user may become sleepy.
In 2004, more than 298,317 people entering drug treatment programs reported marijuana as their primary drug of abuse, showing they needed help to stop using.
In one study conducted in Memphis, Tennessee, 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 display the same lack of coordination on standard "drunk driver" tests as do people who have had too much to drink.
It is common for marijuana users to become engrossed with ordinary sights, sounds, or tastes, and trivial events may seem extremely interesting or funny.