Apparently, according to New Scientist, smoking up lowers our IQ an average of 5 points, and having information overload lowers our IQ an average of 10 points. Not saying whether I buy into it entirely or not, but here are both the Wikipedia and the New Scientist article links:

Information overload - Wikipedia, the free encyclopedia

'Info-mania' dents IQ more than marijuana - info-tech - 22 April 2005 - New Scientist