I'm not sure about that. I know a few people (n<10) that have used soft drugs over a longer time and I remember them as crazy sharp in their younger years and they are very wooly headed now. Concentration problems, simply seem less smart to me. Note that they are heavy users, but still I definitely see a difference there that does not correlate with other people that have gone through a similar stretch of time and that have simply gotten older, but that don't feel less smart, and those don't seem to have concentration issues either.

I'm sure there is a scientific story out there to either confirm or deny this, it's just a personal observation.

yes, i suppose if smoking weed is the focus of your day, that could be the end result. I'm very much a casual user.

I fully support legalization and find marijuana to be relatively harmless compared to other recreational drugs, but comparing it to coffee is ludicrous!

Is that because coffee is far more addictive and has a worse withdrawal?

You mean long term impact right? Because if not you're either very sensitive to coffee or not inhaling or something :)