Mercer Island Reporter, 23 Oct 2012 – We all agree that sniffing glue is not a good idea. It affects cognition. Same with lead paint. We go to great lengths to prevent our kids from being around it since we know that ingestion causes decreased intelligence. A study published this month in "Proceedings of the National Academy of Sciences" shows that smoking marijuana four or more times per week in children under the age of 18 years causes a loss of up to eight IQ points.