I can remember seeing drastic changes in people's personalities throughout my smoking career (which is over)...
when I was in high school I was at this party and this really annoying overly-hyper try-to-hard-to-be-cool jocky football player kid asked to take a hit of my weed... and I let him hit it.
About a month later the kid was a full blown out hippy. Stopped playing football, wore tie die and hemp to school, and within a few months had dread locks in his hair.
But the most shocking thing I noticed was the change in his personality. Suddenly he was calm, cool, and pleasant to talk to. He was no longer annoying. It was a complete 180 degrees from what he used to be. And we became good friends.
That's one of only a couple times I've seen weed change someone so drastically.