I think the worst effect of marijuana is that it turns nice kids from good families into liberals.
When I was a lad in the late 60's and early 70's I received all sorts of anti-drug propaganda. I remember one video in particular featuring Sony Bono were he talked about LSD and tripping and showed some idiot looking in a mirror and seeing a monster face. Um... that didn't do much and all drugs were rolled together as is often done by anti-drug warriors. In fact when many of us did try marijuana the universal reaction was, this is it? This is what they make such a big deal over? This is nothing. For a young person, the refer madness talk was another example of big Government lying to us. If this was a lie, then what else? Suffice it to say that the "Just say no" campaign which came along later for my children, made the same mistake with that generation of young people. The Government did not tell the truth about marijuana. This and Vietnam was only my first examples of doubting the government's stated intentions and I'm sure as hell not a liberal now.