I came clean with my folks a little over a year ago but it was because I orginially come from a very small town where everyone knows EVERYTHING about everyone else, some might know what I mean by that comment, it had gotten out I was doing stronger stuff than I actually was, Mainly I'm just a pot head and occasionally tripper if it ever comes around, and enjoy a good drink every now and then, when I got wind from a ol high school buddy that he heard I was a junkie now, and being from a small town I know how country folk can take stuff and add on twist around and other stuff so when I went to visit my mom for a week-end, I live two hours away but in same state, I sat her down and told her what I have done besides what she might think I have done, after explaining to her I drink but not a big deal cause I am 24 and an adult, that I smoke and occasionaly trip, she is a child of the 60's and was ok with it but didn't like the fact I was doing it, I feel better about it, I never do it around them or anything that is mainly out of respect, but to answer your question, there is a slew of reasons you would or wouldn't tell your parents that you do what you do, personally it has worked for me but I know for some it wouldn't