Although researchers found no irreversible cognitive defects from a lifetime of marijuana consumption, pot users are not a happy lot. In a separate study, most heavy users admitted that the drug has a negative impact on all aspects of their lives from job performance and physical health to mental well being and satisfactory socializing.
Heavy smokers also have substantially smaller incomes and lower levels of education than nonusers or light users, despite the fact that the education and income levels of their families are the same. However, there's no way to determine if marijuana is the cause or if these people naturally have less ambition.
"It's a chicken and egg situation," Pope admits. "Probably the direction of causality goes both ways. In all likelihood, people who become frequent users are somewhat different at the outset; they may have lower cognitive abilities or less motivation. Once they start using the drug regularly, these differences become wider."
Asked if his conclusions would lead him to make any recommendations for or against legalizing marijuana, Pope answered "no, because so many other political and social factors are involved." He noted that alcohol, which is sold legally, causes cognitive deficits in long-term heavy users that do not disappear after 28 days and may be cumulative. However, he adds, "such toxicity is only one factor in the decision."
A number of investigations have linked marijuana to an increased risk of lung cancer. A recent Harvard study concluded that a middle-age person's chance of having a heart attack increases nearly five times during the first hour after smoking pot. That's especially meaningful for baby boomers who developed the habit in their teens and 20s and continue to use the drug in their 30s, 40s, and 50s. Other researchers have associated pot with impaired disease resistance and adverse effects on fetuses when mothers smoke the drug during pregnancy.