I know that a lot of people are saying to drop it, but I would like to get in my two cents really quick.
The college I go to was just recently ranked #8 on the biggest pothead list in the country, so I have been around a lot of it. I have friends who smoke several times a day, and are great people. Intelligent, nice, and do very well in their classes. True, there are some people who are total screwoffs, but ANYTHING that is not done in moderation can cause negative affects physically or psychologically.
I have seen more negative effects come out of people who use alcohol regularly. Just last night a guy I know drank far too much, and had a total freakout, ran away. We spent hours trying to find him and were worried he would become suicidal. I have seen this same guy, along with many others smoke a ton in one night, and sit around really happy, really chill, and do nothing more than have a few laughs and gorge themselves on junkfood.