djcheezwhiz
TRIBE Member
TORONTO (CP) -- It seems Hollywood isn't wrong when it portrays stoners as, well, dumb.
Heavy marijuana use does seem to drive down the IQ, by an average of four points, researchers from Carleton University report in Tuesday's issue of the Canadian Medical Association Journal.
The good news? The decline appears to right itself if the dope smoker butts out.
"A negative effect was not observed among subjects who had previously been heavy users but were no longer using the substance," the researchers wrote.
"We conclude that marijuana does not have a long-term negative impact on global intelligence."
The issue of whether marijuana use has an impact on IQ is a contentious one.
"It's been very controversial," said lead author Peter Fried of Carleton's psychology department. "There have been about 50 studies that have looked at the issue of if there's a residual effect and it's pretty much 50-50."
Resolving the issue has been tough, he said, because of the difficulty of coming up with before and after pictures of each subject's IQ.
About half the studies compared subjects' IQs while under the influence to their IQ after several days of enforced abstinence. But is a few days enough time to ensure the drug has cleared the system and all its neurological effects have worn off?
Fried and his colleagues had a neat answer to the problem. Since 1978, they have been following a group of children whose mothers -- some marijuana users, some not -- enrolled in the Ottawa Prenatal Prospective Study. These children are now aged 17 to 20.
To study the effect of marijuana on IQ, they studied a subset of 70 young adults, comparing current IQ scores to those on file from the subjects' pre-teen days.
"We had the unique opportunity, because of our long-term study, to have IQ measures on these kids before they ever knew the word marijuana," Fried said from Ottawa.
Subjects were asked whether they used the drug and if they did whether their use was light or heavy. Urine samples were analysed to ensure the subjects were being honest about their marijuana use.
Nine of the subjects were light current users and another nine were former marijuana users who had smoked regularly in the past but hadn't used the drug for at least three months. Fifteen were heavy current users and 37 were non-users who had never used the drug on a regular basis.
Current heavy users showed a decline in IQ of 4.1 points, which is in the range of the decrease seen among children whose mothers drank three drinks of alcohol a day while pregnant or who used cocaine during their pregnancy.
But the decrease was not seen among former heavy users.
"This lack of a negative impact among the former heavy users is striking as they smoked, on average, an estimated 5,793 joints over 3.2 years (mean of 37 joints per week); in contrast, the current heavy users had smoked, on average, an estimated 2,386 joints over 3.1 years (mean of 14 joints per week)," the article said.
"Certainly in a low-risk sample -- that's another thing to emphasize -- which these young adults are, it does look like the deficit in IQ, if the people stay clean for three months or so is recoverable," Fried added.
While the results are positive news for recreational marijuana users, he cautioned the findings are preliminary. His team is still studying the subjects to see if there is any impact on attention, memory or other mental functions.
As well, it's not clear the findings can be generalized across the full spectrum of marijuana users. These subjects are middle class with above-average intelligence, kids who don't regularly use other drugs and who are well nourished. The drug's long-term impact might not be the same on someone with a riskier lifestyle, Fried said.
"In the real world out there of course the heavy users probably are poly-drug users, etc. And they may be at a greater risk and their IQ may not recover."
Furthermore, Fried said it would be a leap to conclude that because IQ recovers in young adults who have used marijuana for a few years, 40- and 50-year olds who've been smoking dope for decades can count on the same recovery.
Heavy marijuana use does seem to drive down the IQ, by an average of four points, researchers from Carleton University report in Tuesday's issue of the Canadian Medical Association Journal.
The good news? The decline appears to right itself if the dope smoker butts out.
"A negative effect was not observed among subjects who had previously been heavy users but were no longer using the substance," the researchers wrote.
"We conclude that marijuana does not have a long-term negative impact on global intelligence."
The issue of whether marijuana use has an impact on IQ is a contentious one.
"It's been very controversial," said lead author Peter Fried of Carleton's psychology department. "There have been about 50 studies that have looked at the issue of if there's a residual effect and it's pretty much 50-50."
Resolving the issue has been tough, he said, because of the difficulty of coming up with before and after pictures of each subject's IQ.
About half the studies compared subjects' IQs while under the influence to their IQ after several days of enforced abstinence. But is a few days enough time to ensure the drug has cleared the system and all its neurological effects have worn off?
Fried and his colleagues had a neat answer to the problem. Since 1978, they have been following a group of children whose mothers -- some marijuana users, some not -- enrolled in the Ottawa Prenatal Prospective Study. These children are now aged 17 to 20.
To study the effect of marijuana on IQ, they studied a subset of 70 young adults, comparing current IQ scores to those on file from the subjects' pre-teen days.
"We had the unique opportunity, because of our long-term study, to have IQ measures on these kids before they ever knew the word marijuana," Fried said from Ottawa.
Subjects were asked whether they used the drug and if they did whether their use was light or heavy. Urine samples were analysed to ensure the subjects were being honest about their marijuana use.
Nine of the subjects were light current users and another nine were former marijuana users who had smoked regularly in the past but hadn't used the drug for at least three months. Fifteen were heavy current users and 37 were non-users who had never used the drug on a regular basis.
Current heavy users showed a decline in IQ of 4.1 points, which is in the range of the decrease seen among children whose mothers drank three drinks of alcohol a day while pregnant or who used cocaine during their pregnancy.
But the decrease was not seen among former heavy users.
"This lack of a negative impact among the former heavy users is striking as they smoked, on average, an estimated 5,793 joints over 3.2 years (mean of 37 joints per week); in contrast, the current heavy users had smoked, on average, an estimated 2,386 joints over 3.1 years (mean of 14 joints per week)," the article said.
"Certainly in a low-risk sample -- that's another thing to emphasize -- which these young adults are, it does look like the deficit in IQ, if the people stay clean for three months or so is recoverable," Fried added.
While the results are positive news for recreational marijuana users, he cautioned the findings are preliminary. His team is still studying the subjects to see if there is any impact on attention, memory or other mental functions.
As well, it's not clear the findings can be generalized across the full spectrum of marijuana users. These subjects are middle class with above-average intelligence, kids who don't regularly use other drugs and who are well nourished. The drug's long-term impact might not be the same on someone with a riskier lifestyle, Fried said.
"In the real world out there of course the heavy users probably are poly-drug users, etc. And they may be at a greater risk and their IQ may not recover."
Furthermore, Fried said it would be a leap to conclude that because IQ recovers in young adults who have used marijuana for a few years, 40- and 50-year olds who've been smoking dope for decades can count on the same recovery.
