Here's a link that MaryJaneScott provided us with, and I think it really explains the different drugs and how they react with your brain. Very informative.
http://learn.genetics.utah.edu/units...rugs/mouse.cfm
Marijuana won't fuck up your life, nor will any other drug for that matter. It all comes down to an individual's decision to make the right, logical choices when it comes to those things. It's just that a bunch of ignorant people give certain drugs horrible reputations, weed included.
And really, who the hell cares about short-term memory? Think about it. In 20 years, will it really matter if you can't remember what you had for breakfast 20 years prior? Of course not. Most info that our short-term memory processes is useless anyway, so there's no point in preserving something like that. My long-term memory is as sharp as ever, and I've been a daily smoker for somewhere around 4 years.