I have spent a very long time scouring the internet trying to find some sort of information on this and come up with next to nothing. I know there are numerous studies out there that show that driving while under the influence of THC is not nearly as bad as alcohol, it still can impair your driving. All of my friends claim that you are fine to drive just a couple of hours after smoking. I would think that one would need at least 4 hours or so to be okay, but i don't really have any scientific evidence of how long marijuana affects someone. It's very easy to figure out how long you need to wait to drive after drinking...there are BAC calculators that can do an approximation calculation based on the amount of alcohol consumed, gender, and body weight...while certainly not precise, responsible people can use such calculators to make responsible decisions about whether or not to drive. How can the same responsible person make a decision about whether or not to drive after using marijuana? I can't seem to find any resource on the subject, and until I can find some sort of credible information I know that my friends will continue to believe that it's okay to drive say 2 hours after smoking. All of the studies I've read test driving impairment 30 minutes after smoking which of course you're still going to be impaired after half an hour. Yes, I have read the studies that all say that it's not as bad as having alcohol in your system, but I still think it's very important to be able to drive without a significant degree of impairment. What would be the equivalent of having a miniscule BAC (.01 or .02) for marijuana? How long after consumption would it take to go down to that? Anyone have any information on the subject? Would k9copper or niteshift like to respond? I think this is a very important issue, and I'm surprised I can't find information on it more easily. p.s. as a sidenote i'm not really sure where to post this, but this forum seems okay because the discussion is mostly about legal topics and this topic fits into that category in a very large way...at least insofar as when is it ethically okay to get behind the wheel.