Paul ADEPOJU

A new study has shown that teenagers who smoke marijuana frequently are pre-disposing themselves to declines in intelligence and mental function that persist well into adulthood.

According to the results of a ten-year study conducted in New Zealand and involving more than 1,000 volunteers, researchers found that adolescents who smoked marijuana at least four days per week lost an average of eight IQ points between the ages of 13 and 38, a pattern not seen among people who began smoking heavily only in adulthood.

"Heavy pot smokers tend to show deficits in memory, concentration, and overall brainpower in relation to their peers, but these problems were more pronounced - and seemingly more lasting - among those who picked up the habit as teens," said the researchers in the study report.

According to the study, individuals who smoked heavily in adolescence had consistently lower IQs at age 38, even if they'd cut back in the previous year. By contrast, the IQ of the relative latecomers to marijuana was more closely linked with how much pot they'd smoked recently.

"The effect of persistent cannabis use on intellectual functioning is really confined to adolescents, (which) suggests that adolescents, in particular, are vulnerable to the effect of cannabis," says lead author Madeline H. Meier, a psychologist and postdoctoral researcher at Duke University in Durham, North Carolina.

An eight-point decline in IQ isn't negligible, the authors say. Previous research suggests a drop in intelligence of that magnitude could, for instance, affect a person's long-term career prospects, job performance and income.
It's reasonable to suspect that still-growing teen brains might be especially sensitive to the cumulative effects of marijuana, says Dr. Jeffrey Brosco, a professor of pediatrics at the University of Miami's Miller School of Medicine.

"In the developing brain, neurons are growing and changing, synapses are forming," says Brosco, who was not involved in the study. "When there's a lot of change in any part of the body, particularly the brain, that usually means it's more vulnerable to environmental influences."
(CNN)