I have been smoking weed on a daily basis for two years now, and looking back I wanna fucking kill myself 'cause it is so fucking stupid. Weed, just like any other drug, can be abused and when you smoke as much of it as I have you realize its a waste of money, time- pretty much just a waste. I'm 3 days sober atm and the nights suck but I can not wait till my body stops feelings the effects of not smoking. Smoking weed every one in a while is no big deal, and I still plan on smoking just not nearly as much as I used to. My advice is if you haven't started smoking weed, don't. I'm at the point where when I'm high I just feel disgusted with myself and depressed. I used to be the biggest pothead and I can't believe im saying this, but fuck weed.
I think a lot of the times it depends on what age you start smoking weed. I believe if you start smoking in your mid 20's and do it consistently than you are more than likely going to be fine. If you start when you are in your early teens like 12 or 13 years old you have a possibility of being mentally fucked. I know a guy who started when he was 12 and he's 20 now and weed has totally ruined his personality. Just no energy and not much passion for anything when he talks. That's one of the main bad effects I would say it could have especially if you start out a dumbass you are going to be a bigger dumbass.