First off, I've smoked a LOT of weed.
I started just like every kid with the attitude that ALL illegal drugs are bad. That attitude slowly wore away to I'll give weed a go, after doing quite a bit of research. My attitude then transformed into
"OMG OMG OMG, weeds so good for you, it's not even bad for your health, there's no negative effects, no mental health issues, no motivation loss, nothing OMG OMG OMG"
That was after reading all the pro cannabis "research" papers. After buying an ounce and smoking everyday for about a month, I decided I seriously needed to re-consider my (ab)use. It lead to me being very depressed, unmotivated, slow, and I lost all of my self esteem. I couldn't look people in the eye for some reason. My university course work was suffering and I wasn't going to sweet FA classes. I lost my spark and quick wit. I was in a constant haze and I was sleeping like 12 hours a day. After that 1 month period, I WAS a fucking dumb ass.
All I did was mope around, smoke dope and eat food.
I have since done MDMA, acid, amphetamine, salvia, mushrooms and mephedrone, as my attitude toward drugs has changed.
Now I'm not saying weed is bad, quite the contrary. I still smoke now and then, and plan to do it quite a bit over summer. But it affects everyone differently. I'm one of those people who either want to go in bed and watch movies or just fall asleep. I cannot socialise when I'm high. At all. Talking to me high is like talking to a zombie.
I have friends who smoke every day and they are almost better people because of it. They get shit done, they are still just as intelligent and social. Weed for me is something I do in my own time to relax (very rarely), never if I have to be around people.
For the record I was valedictorian of my high school. Not claiming, my high school was pretty small and I'm not particularly intelligent.
I'm certain that if I hadn't of slowed down my weed use, I would suffer mental illness later in life. The early signs were there, I was not in a good head space after smoking too much.
What I'm trying to say is it has different effects for everyone. People who react to it like me should not use it too much, it will fuck up your life. Other people who react better should go ahead and smoke it all day long, fuck I would.