term marijuana use may create changes in the brain that make a person more at risk of becoming addicted to other drugs, such as alcohol or cocaine. While not all young people who use marijuana go on to use other drugs, further research is needed to predict who will be at greatest risk. Marijuana has serious harmful effects on the skills required to drive safely: alertness, the ability to concentrate, coordination, and the ability to react quickly. These effects can last up to 24 hours after smoking marijuana. 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 have also shown 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. Doctors advise pregnant women not to use any drugs because they could harm the growing fetus. One animal study has linked marijuana use to loss of the fetus very early in pregnancy. Some scientific studies have found that babies born to marijuana users were shorter, weighed less, and had smaller head sizes than those born to mothers who did not use the drug. There are also research data showing nervous system problems in children of mothers who smoked marijuana. Researchers are not certain whether a newborn baby's health problems, if they are caused by marijuana, will continue as the child grows. Preliminary research shows that children born to mothers who used marijuana regularly during pregnancy may have trouble concentrating. Some studies show that when people have smoked large amounts of marijuana for years, the drug takes its toll on mental functions. Heavy or daily use of marijuana affects the parts of the brain that control memory, attention, and learning. A working short-term memory is needed to learn and perform tasks th...
