Adults aged eighteen to twenty-five have the highest rate of cocaine use. Crack cocaine is powder cocaine that has been processed into a form that can be smoked. Crack and cocaine can cause heart attacks and brain hemorrhages and sometimes have fatal effects. During the 1980s, the low cost of crack and its ability to produce an almost immediate effect made it very popular. Although cocaine and crack use has declined since then, these drugs remain a serious problem. UNITED STATES. Smoking marijuana produces a general feeling of well-being, but also impairs a person's judgment and reaction time and decreases coordination. According to the 2009 Youth Risk Behavior Survey, 38 percent of students in ninth through twelfth grades in public and private schools in the United States had used marijuana one or more times during their schooling..