Smoke up and your attention span will go up in smoke, found a study released in yesterday's Journal of the American Medical Association.

The study, conducted by a team of researchers at Harvard McLean's Hospital, surveyed a group of college students and found that heavy marijuana smokers (those smoking an average of 29 days per month) suffer from reduced cognitive abilities and attention impairment even after a full day of not using the drug.

One of the study's coordinators, Harrison G. Pope Jr. '69, chief of the Biological Psychiatry Laboratory, said the study was conducted to determine whether marijuana use has long-term effects.

Pope said the study controlled for flaws found in similar, earlier studies, such as the possibility that subjects might have been previously impaired, or that marijuana users might also use other drugs.

Pope added that subjects were continuously supervised to prevent them from smoking overnight.

The money to pay for people to conduct the supervision came from a National Institute of Mental Health grant, according to Pope.

But he noted that there is still work to be done in this area.

Pope said he hopes to make sure that the short period of exposure and the young age of the subjects (most were undergraduates) did not influence the study's findings.

"We may have underestimated the effect of marijuana, because we were looking at young college students who had only been smoking for a few years," Pope said.

According to Pope, subjects for his next study will be "people who have smoked 5,000 separate times in their lives--once a day for 13 years or more--and...look at these people not just one day after they stop smoking, but again seven days and 28 days after they stop smoking."