Marijuana use can make it difficult to judge distances and react to signals and sounds on the road. Marijuana may play a role in car accidents. 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.
Smaller babies are more likely to develop health problems.
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. 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 that call for more than one or two steps.