Scientists do not yet have all the answers about the health effects of marijuana, but those they know of--plus those they suspect--are cause for “serious national concern,” according to a National Academy of Sciences (nas) report released here last week.
The steep rise in marijuana use--now leveling off--among school-age Americans, and their use of the drug during school hours, suggests that the situation may pose a more serious problem for schools than does the use of alcohol, the report says.
Health Jeopardized
Countering claims that the drug--now the most widely used illicit drug in the U.S.--is safe and should be legalized, the panel of medical experts found evidence to support a variety of effects that could jeopardize the health of users.
Drawing their conclusions from a large body of published research, the panel reported that marijuana appears to do the following:
Impair motor coordination;
Affect “tracking” ability--the act of following a moving stimulus--and other functions related to perception;
Impair short-term memory;
Slow learning; and
Cause damage to the lungs and respiratory tract, much like the damage caused by tobacco smoke.
So far, the researchers say, there is no conclusive evidence that marijuana use affects fertility in either males or females, and studies to date have offered no definitive evidence that the drug causes birth-defects or genetic damage in humans.
‘Steep Rise’ in Use
The potential hazards--physiological and psychological--associated with the drug may be a particular threat to the school-age population, the panel of medical and scientific experts cautioned. “There has been a steep rise in its use during the past decade, particularly among adolescents and young adults,” write the authors of the report, Marijuana and Health.
And although a greater percentage of high-school students have tried alcohol than have tried marijuana, marijuana is favored by more high-school seniors for daily or near-daily use; 9 percent of all high-school seniors use marijuana almost every day, compared with 6 percent who use alcohol that regularly, according to the panel.
The drug’s effects on education may be more direct than those of alcohol, too, the report suggests.
Unlike alcohol, which is primarily consumed away from the schools, marijuana use is increasingly common during school hours. “Much of the heavy use of marijuana ... takes place in school, where effects on behavior, cognition, and psychomotor performance can be particularly disturbing,” according to the panel’s report.
Behavior Affected
Moreover, it asserts, the most well-documented effects of marijuana are those involving the mental and neurological processes--processes that also govern learning. “We can say with confidence,” the researchers write, “that marijuana produces acute effects on the brain, including chemical and electrophysiological changes. Its most clearly established acute [short-term] effects are on mental functions and behavior.”
Some of the effects noted by the panel have received little attention in anti-drug campaigns. For example, the drug has short-term effects on the heart and lungs; it raises the heart rate and, in some persons, the blood pressure.
These effects, according to the report, could be particularly hazardous to people with high-blood pressure, heart disease, or vascular disorders.
Marijuana also seems to affect the respiratory system in a way that is potentially as life-threatening as tobacco, according to the panel. Many of the chemical compounds found in the drug are similar to those found in tobacco--including “tar"--and the biological effects are similar to those of tobacco.
Impairment Possible
“This suggests the strong possibility that prolonged heavy smoking of marijuana, like tobacco, will lead to cancer of the respiratory tract and to serious impairment of lung function,” the panel writes.
But so far, the panel says, there is no conclusive evidence that prolonged use of marijuana causes permanent changes in the nervous system or sustained impairment of brain function and behavior in humans.
Neither is it possible to tell from the evidence available whether the mental disorders and behavioral dysfunctions that are associated with chronic, heavy marijuana use are a cause or an effect of the drug use.
‘Stepping Stone’
The cause-and-effect link between marijuana use and use of other drugs is similarly clouded. “Association does not prove a causal relation,” according to the panel, “and the use of marijuana may merely be symptomatic of an underlying disposition to use psychoactive drugs rather than a ‘stepping stone’ to involvement with more dangerous substances.”
The same argument precludes researchers from indicting marijuana as the cause of the lack of motivation frequently seen in users; “amotivational” persons may simply be more drawn to illicit drugs, according to the report.
