The main hassle in Medellin can come from the guys in uniforms, (police/army/whatever), keep contact with them to a minimum, avoid eye contact, don't dress flash, hunker down if you're tall. There are most certainly parts of the city that you do not want to visit after dark - and it gets dark early. I found it best to look poor, shabby clothes, no wristwatch, no camera,and always at least try to appear as though you know exactly where you are and where you are going, with a look on your face that says "Don't even think of mugging me". During daylight life goes along fairly normally. Scoring weed is no problem, any market, but of course don't let anyone see more than they have to, no money up front. Charlie can vary greatly but will probably be the best you'll ever have. It cost about 1/50th of the price back home making it almost value for money. Larger amounts can be safely aquired but truly be careful as there are people willing to kill for $200.