Students who smoke marijuana get lower grades and are less likely to graduate from high school, compared with their nonsmoking peers. A study of 129 college students found that, among those who smoked the drug at least 27 of the 30 days prior to being surveyed, critical skills related to attention, memory, and learning were significantly impaired, even after the students had not taken the drug for at least 24 hours.

These "heavy" marijuana abusers had more trouble sustaining and shifting their attention and in registering, organizing, and using information than did the study participants who had abused marijuana no more than 3 of the previous 30 days. As a result, someone who smokes marijuana every day may be functioning at a reduced intellectual level all of the time.

More recently, the same researchers showed that the ability of a group of long-term heavy marijuana abusers to recall words from a list remained impaired for a week after quitting, but returned to normal within 4 weeks. Thus, some cognitive abilities may be restored in individuals who quit smoking marijuana, even after long-term heavy use.

Workers who smoke marijuana are more likely than their coworkers to have problems on the job. Several studies associate workers' marijuana smoking with increased absences, tardiness, accidents, workers' compensation claims, and job turnover.

A study among postal workers found that employees who tested positive for marijuana on a pre-employment urine drug test had 55 percent more industrial accidents, 85 percent more injuries, and a 75-percent increase in absenteeism compared with those who tested negative for marijuana use. In another study, heavy marijuana abusers reported that the drug impaired several important measures of life achievement including cognitive abilities, career status, social life, and physical and mental health.

Research has shown that some babies born to women who abused marijuana during their pregnancies display altered responses to visual stimuli, increased tremulousness, and a high-pitched cry, which may indicate neurological problems in development.

During the preschool years, marijuana-exposed children have been observed to perform tasks involving sustained attention and memory more poorly than non-exposed children do. In the school years, these children are more likely to exhibit deficits in problem-solving skills, memory, and the ability to remain attentive. Long-term marijuana abuse can lead to addiction for some people. That is, they abuse the drug compulsively even though it interferes with family, school, work, and recreational activities. Drug craving and withdrawal symptoms can make it hard for long-term marijuana smokers to stop abusing the drug. People trying to quit report irritability, sleeplessness, and anxiety. They also display increased aggression on psychological tests, peaking approximately one week after the last use of the drug.