"Taking deep tokes and holding in smoke for a long time is very harmful to the lungs. THC is actually absorbed quickly by the lungs, and the longer you hold it in the more tar will be absorbed. Although this behaviour - to get the biggest bang for your buck - is the product of the illegal and overpriced status of cannabis, it is the main reason that smoking one joint of cannabis is thought to be more harmful than one tobacco cigarette."

http://www.norml.org.nz/page26.html

5-7 isn't what i would call a "long time" .. 10 seconds? 15? yea.. that's getting a bit excessive.