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
micko Reviewed by micko on . Information overload vs effect of mj This is kind of interesting (from Wikipedia). I've got a lot of things, stressful things, going on, and my brain definitely shuts down at times... then I have the thinking capacity of Homer Simpson:o . Anyone else get this? "Information overload is a term that refers to the state of having too much information to make a decision or remain informed about a topic. Large amounts of information to dig through, a high rate of new information being added, contradictions in available information, Rating: 5