In a study published last week in the Proceedings of the National Academy of Sciences, researchers followed the IQ scores of 1,000 participants from New Zealand, ages 13-38. They were tested starting at 13, then again at 18 and finally at 38.
When participants were asked if they smoked marijuana frequently, 52 indicated they did by age 18, and 92 others said they started after they were 18. As researchers compared scores, they noticed about an 8-point drop in IQ points by participants who started smoking by 18.
Dr. Eric Houchin, a primary care physician for North Ottawa Family Practice, said heavy pot use is considered smoking more than five joints a week during a three-month period. Although the person is impaired while smoking marijuana, Houchin said there are long-term effects including memory problems, trouble with time perception and slowed information processing.
In addition, Houchin said they’ve seen brain scans where the executive decision portion of the brain actually shrinks. Even if the patient stops smoking, that portion of the brain doesn’t appear to grow, which leads doctors to believe neurocognitive change is permanent, he said.
The 2011 Ottawa County Youth Assessment Survey, administered to students in grades 8-12, indicated that 26.1 percent "perceived no or (a) slight risk to smoking marijuana regularly.” That number is up from 19.1 percent in 2009, 16.6 percent in 2007 and 11.6 percent in 2005.
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